ERICSSON REVIEW. Vol. XXXIX 1962 CONTENTS

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3 ERICSSON REVIEW Vol. XXXIX RESPONSIBLE PUBLISHER: HUGO LINDBERG EDITOR: SIGVRD EKLUND, DHS EDITOR'S OFFICE: STOCKHOLM SUBSCRIPTIONS: ONE YER $ :0; ONE COPY $ 0:0 CONTENTS TELEPHONE OPERTION Planning of Multi-Exchange Networks with id of a Computer I. Location and Boundaries of Exchanges in Multi-Exhange reas page II. Inter-Exchange Traffic III. Planning of Junction Circuits in Multi-Exchange Networks. Some Fundamental Principles 0 Practical pplication of Planning of Multi-Exchange Networks with id of a Computer. Exchange Locations and Boundaries 0 TELEPHONE EXCHNGES ND SWITCHBORDS Crossbar Private utomatic Branch Exchange (P..B.X.) for 0 and Extensions Crossbar System RK 0 for Rural Exchanges. Exchange Types Crossbar P..B.X. RD Portable 0-line Switchboard LONG DISTNCE TELEPHONY n Experimental Data Transmission System The Development and Future of Wide Band Carrier Systems 0 Transistorized Group Translating Equipment for Carrier Terminals CO M PONENTS The Dry Reed Switch a Sealed Contact of Great Reliability

4 MESURING ND TEST INSTRUMENTS page Duration Meter VMF 0 MISCELLNEOUS L M Ericsson Exchanges Cut into Service % L M Ericsson News from ll Quarters of the World l )»»»»»»»»»»»»»»»»»»»»»»»»»»» COPYRIGHT TELEFONKTIEBOLGET LM ERICSSON PRINTED IN SWEDEN, ESSELTE B, STOCKHOLM

5 ERICSSON REVIEW Vol. XXXIX No. I RESPONSIBLE PUBLISHER: HUGO LINDBERG EDITOR: SIGVRD EKLUND, DHS EDITOR'S OFFICE: STOCKHOLM SUBSCRIPTIONS: ONE YER?.0; ONE COPY $ 0.0 CONTENTS Crossbar System RK 0 for Rural Exchanges. Exchange Types Crossbar Private utomatic Branch Exchanges (P..B.X.) for 0 and Extensions L M Ericsson Exchanges Cut into Service L M Ericsson News from ll Quarters of the World On cover: Forming of Cables for Telephone Relay Sets and Registers at L M Ericsson's Head Factory, Midsommarkransen, Stockholm. COPYRIGHT TELEFONKTIEBOLGET LM ERICSSON PRINTED IN SWEDEN, ESSELTE B, STOCKHOLM

6 Crossbar System RK 0 for Rural Exchanges Exchange Types R BGER, TELEFONKTIEBOLGET LM ERICSSON, STOCKHOLM UDCE.. LME The general principles of crossbar system RK 0 were outlined in Ericsson Review No... In this continuation of the previous article the various types of exchange covered by this system. RK and RK for terminal exchanges, and RK for group centres, are presented. The article concludes with some examples of the use of the RK 0 system. Terminal Exchange Type RK Terminal exchange type RK has an initial capacity of 0 subscriber lines and is extendable in units of 0 lines up to 0 lines. Fig. shows the trunking diagrams and grouping plans for RK at different stages of growth. n exchange for 0 lines is equipped with a single crossbar switch SL. and there are thus 0 verticals available for connection of cord circuits SNR. junction circuits FDR and local registers REC-L. For 0 lines two crossbar switches are used, grouped so that each unit of 0 subscriber lines has access to verticals. These verticals in each unit are connected in parallel, so that inlets and outlets are available for SNR. FDR and REC-L. RK / can be extended by a further 0 lines up to 0 subscriber lines by addition of two crossbar switches with verticals, which serve the extra 0 lines and are wired in parallel with the remaining verticals. The number of available inlets and outlets is thus not increased, but remains as in the 0-line case. X Fig. X Trunking diagrams and grouping plans for terminal exchange RK, 0, 0 and 0 lines ll crossbar switches have 0 three-pole outlets per vertical. The marker is equipped for connection of two REG-L. six SNR and seven FDR. In the disposal of inlets and outlets for SNR, FDR and REG-L. it must be observed that every SNR occupies two verticals. f^wt-] Croup centre 0 subscriber lines o o o o 0 subscriber lines o o o o o o 0 subscriber lines M c ig rv» 0 0 f\.ls W* ] Croup centre Group centre SLI SL SNR -*~FDR REG-L SLI SL SLi - i>- i>- t>-t> - - ir- -b HJ SNR FDR REG-L SLI SLi SLS ^ i>-b -^> J<i SL LV SNR FDR REG-L

7 MDF -T\- LR SUBS LINE ccr. $ SLI SELECTOR STGE CORD CCT. JUNCTION CIRCUIT GROUP CENTRE SL- LOCL REGISTER Not Fig. Block diagram for terminal exchange RK LR 0- W- LL VF \GENERTOt CODE RECEIVER LOCL- REGISTER No SNU L J_J U Functions of Switching Units The block diagram in fig., shows in main outline the switching equipment employed in RK. Marker (M): controls the connection of the selector stage SL. The exchange can be equipped with only one marker. Code receiver (KM): is equipped with a v.f. receiver for six frequencies and a sender for four frequencies, and with relays for storage of digital information. KM also contains relays for connection of junction circuits FDR. The exchange can be equipped with only one KM. V.f. generator (TG): supplies the sender equipment in KM with four voice frequencies. Local register (REG-L): is seized if all junction circuits are engaged. It can control the setting up of an internal (local) connection within the exchange, but returns busy tone and is released if the call is external. The exchange can be equipped with two REG-L. Cord circuit (SNR): contains the necessary relay equipment for local connections. The exchange can be equipped with six cord circuits. Junction circuit equipment (FDR): contains the necessary relays for outgoing and incoming external connections. The exchange can be equipped with seven FDR. Switching Processes Since the switching processes in RK and RK are essentially identical, they will be described with reference to the latter type. Mechanical Design The equipment is mounted on two racks 0 mm (' ") high and 0 mm (' ") wide. ll units, both switches and relay sets, are of plug-and-jack type. One rack contains all basic equipment for RK and switching units for 0 subscriber lines. The other rack is used for extension to 0 or 0 subscriber lines and contains the equipment necessary for this purpose. The two racks can be set up side by side or back to back. t the bottom are jacks which take plug-ended cords for interconnection of the two racks.

8 SL SLB ±~f line groups BM *fg-i Group centre tine groups X _., X r'g- J X Trunking diagrams for terminal exchange RK Line group for 00 subscriber lines: 0 SL and 0 SLB verticals Max. number of verticals: 00 SLC, 0 SLD SL SLB SLC ^HH^ S 0 line groups I BM CM SLD DM I SNR [ I,' KM -Group centre Terminal Exchange Type RK The subscriber stage is built up of two selector stages SL and SLB, which serve 00 lines. Each such line group usually has 0 SL verticals and 0 SLB verticals. s the capacity of the exchange increases, additional line groups will be required, being connected to SLC, and ultimately SLD, stages as shown in the trunking diagram in fig.. To the SLC (SLD) verticals are connected cord circuits SNR, junction circuits FDR for two-way traffic (or FIR for incoming and FUR for outgoing traffic), and local registers REG-L. If there is an SLD stage, one side of SNR is connected to SLC verticals. Fig. X X Line group for 00 subscriber lines, terminal exchange RK The switching functions within the SL and SLB stages are performed by markers BM. which can be connected to all line groups. The exchange can be equipped with either one or two BM, which can operate simultaneously in different line groups. With SLC and SLD stages, C and D marker (CM and DM) must be added, which must be duplicated if the exchange has two BM. Duplicated CM and DM can connect simultaneously to their respective SLC and SLD selectors. Up to five code receivers KM and up to seven local registers 0 subscri ier lines 0-0'SO subscriber lines t 0 O O O O O O O O O O O O -o -o -o -o -o -o -o 0 -o -o -o V S -o-o-o H S -O-O -O -( -O-O-O i 0 *., ' 0-digit directly to SLB 0 is connected 0-digit Z V -o -o -o -? -o -o -s -o -o SL SL [O] ^' f^ <" SLB r SNR,FDR,REG-L or SLC SLBt SNR FDR or SLC RES-L,, a s s s 0? s 0 Subscriber numbering SL l SLB Trucking diagram SLBZ Grouping plan

9 Fig. SL MM w J Grouping plaas for RK T " " I t SLB lines X X X \o-o -o-o-o-o-o-o-o-o ] t \o -o -o -o -o -o -o -o o -o" o-oo-o-o-o-o-oo-o [-Q-Q -O-O-O-O-OQ-Q -<j V [O-O-O-O-OO-Q-O-O o[ o-o-o-o-o-o-o-o-o-o [ o-o-o-o-o-o-o-o-o-o] I ' SNR,REC-L,FDR \ I " SL SLB lines SLC i t T I } } } } } } } } ) f! SL SLB o-o-o-o-o-o-o-o-o-<: ] -o-o -o^>-o-o-o-o-o-<] J -o-o-o-o-o-o-o-o-o~ -o-o-o-o-o-o-o-o-o-ol f ^-O-O-O-C ] J si r -o-o-o-o-o-oo-o-o-o -o-o-oo-o-oo-o-o-c ] «}M} o-o-o-o-o-o^)-o^>-c ] a -o-o-o-o-o-o-o-o-o< ] w ^ ^ - ^ ^ -..,. - SNR ^ ^ s-^ ^ ^,. SNR 'REG-L FDR i j h S d SLD ^ S 0 -o-o-o-o-o-o-o-o-o-o -o-o-o-o-o-o-o-o-o-o -o-o-o-o-o-o-o-o-o-o o-o-o-o-o-o-o-o-o-o -o-o-o-o-o-o-o-o-o-o -o-o-o-o-o-o-o-o-o-o o-o-o-o-o-o-o-o-o-o o-o-o-o-o-o-o-o-o-o o-o-o-o-o-o-o-o-o-o O-O-O-O-O-O-O-O-O-O -O-OO-O-O-O-O-O-OO -OO-O-O-O-O-O-O-O-O o-o-o-o-o-o-o-o-o-o -o-o-o-o-o-o-o-o-o-o -o-oo-o-o-oo-o-o-o -o-ooo-o-o-o-o-o-o -O0-0-OK) o-oo-o-o-o-o-o-o-o ooo-o-o-o-o-o-o-o b V J B 0 ; f» IS SLD lines * '" c/ r ii it it if: l? IS 0 -~SNR SLL SNR ~ REC-L FDR REG-L may be installed, but the total number of KM and REG-L exceed seven. cannot Installed for 00 subscriber lines, the exchange has two SL and two SLB crossbar switches as shown in fig.. In both selector stages the crossbar switches have 0 three-pole outlets per vertical. 0 lines are connected to the SL multiple, where they have access to six or seven verticals, and 0 lines to the SLB multiple with full availability. These 0 lines can therefore be employed for subscribers with specially high traffic. The SL multiple is transposed so that the 0 subscriber lines form groups of 0 lines to which there is access from the various vertical groups in SL I and SL. To the 0 SLB verticals are connected cord circuits SNR, junction circuits and local registers REG-L. For more than 00 lines, additional line groups must be introduced as well as an SLC stage the multiple of which terminates on the SLB verticals in the various line groups. When the capacity exceeds 00 lines, SLD stages are required, the multiple outlets of which terminate on the SLC verticals. In the SLC and SLD stages the crossbar switches have 0 four-pole outlets per vertical. Fig. shows an example of selector groupings for different sizes of exchange. The grading between SLC and SLB can be arranged so that either 0.,,

10 or vertical in each SLB crossbar switch is accessible from a group of SLC crossbar switches with common multiple. The SLB-SLC and SLC-SLD links pass through an I.D.F., so that it is possible to adapt the groupings and the number of SLC and SLD switches to the actual requirements. Fig. Block diagram tor terminal exchange RK Switching Units and Their Functions The block diagram in fig. shows in main outline the switching equipment in RK. B connector (MIR-B): is associated with a specific line group for max. 00 subscriber lines, its function being to connect a free marker to the subscriber line equipments LR and to the SL/SLB switches of that line group. Each line group installed requires one MIR-B. and an exchange can have at most 0 of these units (,000 lines). B marker (BM): supervises the line groups (the SL/SLB system can be equipped with max. two BM per exchange. stages). The C marker (CM): supervises the SLC stage, which can have 00 verticals. The number of CM is limited to two. D marker (DM): supervises the SLD stage and is equipped for 0 SLD verticals. In RK. however, there are not usually more than 0 SLD verticals. maximum of two DM can be installed. Marker connector (MIR-REG): connects cord circuits (SNR), local registers (REG-L) and code receivers (KM) to the marker equipments. Type RK can be equipped with only one MIR REG. Code receiver connector (FID): connects the junction circuit relay sets (FDR. FIR. FUR) to code receivers KM. Every FID unit has a capacity of five circuits and two KM. and can connect one of these five circuits to a KM. CORD CCT. MDF S-^Jf LR SL SL, ID IDF SLC <r~t SLD FDR(FIR,FUR) JUNCTION CIRCUIT GROUP ' CENTRE LINE GROUP W SLC-STGS SLD-STGE LOCL REGISTER LINE GROUP No. B- CONNECTOR MRKER NO e FDR 'FIR.FUR) LINE GROUP No. B- C0NNECT0R MIR-RES MRKER CONNECTOR no CODE RFC CONNECTOR VF GENER0R LINE GROUP No!0 CODE RECE!VER No.

11 Code receiver (KM): is equipped with a v.f. receiver for six frequencies and a sender for four frequencies and with relays for storage etc. of the received digital information. The system permits connection of max. five code receivers. V.f. generator (TC): supplies the sender equipment in KM with four voice frequencies. Swit ch ing Pro cesses Outgoing calls On a call from an RK subscriber, MIRB is seized and connects to a free BM. The subscriber's position in the SL multiple and the subscriber category are ascertained. With the aid of CM and DM a free junction relay set FDR to the group centre is seized, and stages SL, SLB, SLC and SLD are set up to the FDR. t the same time a code receiver KM is connected via FID to the selected FDR, and. receives information of the subscriber category from BM. On request from the group centre register for transmission of category, this is sent by MFC signalling from KM. which thereupon releases. Dial tone is returned from the group centre register and the subscriber dials the wanted number. The pulses are repeated by FDR and sent over the junction to the group centre. Call-back to terminal exchange If the group centre register decides that an attempt should be made to connect back to the originating exchange, FDR receives a KM seizure signal which connects a free KM to FDR via FID. In FDR the connection is broken between the subscriber side and the line side, so preventing any repetition of the dial pulses. KM receives the numerical information in MFC from the group centre, ascertains whether the called party can be reached via the originating exchange or not, and returns the corresponding controlling signal to the group centre. Local connection If the called subscriber belongs to the same exchange as the caller, a local connection is set up as soon as KM has received full information of the number. KM calls an BM and transmits to it the called subscriber's number. BM ascertains whether the called party's line is free and, is so, a signal is sent from KM via FDR. SLD, SLC. SLB and SL to the calling subscriber's line equipment, so placing a marking condition on it. ll selector stages are released and the marker equipment sets up a new connection between the calling and called subscribers' lines via SL, SLB, SLC. SLD. SNR. SLC, SLB and SL. after which the marker equipment releases. line-free signal is sent by MFC to the group centre from KM, which receives from the group centre a connection-complete signal which clears FDR and the junction line. t the same time KM is released and ringing signals and ringing tone are sent from SNR. If the called party is engaged or intercepted, BM releases. Before KM releases, it signals the line condition to the group centre, from which a busy or interception tone is sent (or the connection is switched to an operator). The junction circuit and selector stages are cleared when the calling subscriber replaces his handset. If the caller does not replace, a forced release signal is received from the group centre within about seconds and the subscriber is placed on line lock-out and receives busy tone from his line equipment. Connection to direct junction If the called subscriber is on an exchange with a direct junction from the calling exchange, a free circuit on the route is seized as soon as KM has received sufficient numerical information. The calling subscriber is connected to the circuit, the previous connection being held in the meantime. KM connects to the circuit via a bypath, and a code receiver is connected at the destination exchange in the normal manner. Before the group centre starts to send the first digit required by the destination exchange, the KM in the originating exchange has switched over so that

12 ," ', R. ~ ' 000 " KK 00 fg'fp* r ' i esse S''! i?00 'l.'i laoo j? ^ J'" t'" n ' ' II KK /r I - s» J - r-h J w [ ; «' > M«r ll II "[ ws* C i II ' II II 00 /ines 00 lines 000 lines Fig. X Floor layouts for terminal exchange RK Rack SL. SLB and line equipment. 00 subscriber lines, Marker and code receiver Code receiver SLC, SLD crossbar switches with markers SLC (SLD) crossbar switches Cord circuits and junction circuits MK I.D.F. KK B IT SM M.D.F. Battery Rectifier Subscribers' meters Rack height: 00 mm (' 0 ) Free ceiling height: 000 mm (' 0") it responds solely to numerical signals -. The digits from the group centre therefore pass this KM and continue to a code receiver at the destination exchange, which returns information of the line condition in the normal manner (free, engaged, intercepted), as soon as it has received complete information of the number. If the called party is free, the group centre returns numerical signal. The KM at the originating exchange responds to this signal and releases. The junction circuit to the group centre and the selector stages are cleared, whereas the connection from the calling subscriber via SL. SLB, SLC and SLD to the selected direct junction is held. If the called party is engaged or intercepted, the group centre sends numerical signal //, which is picked up by the KM at the originating exchange, whereupon KM releases. The connection to the direct junction is cleared, but the connection to the group centre is held and busy or interception tone is returned from the group centre as previously described (or the connection is directed to an interception operator). The called party cannot be reached direct from the originating exchange If KM ascertains from the received digital information that the called party is not accessible via the originating exchange or via a direct junction, this is signalled to the group centre, which sends numerical signal //to KM. FDR is thereby through-connected once again to the group centre and the first ringing tone is sent from KM before the latter releases. No call-hack to originating exchange If the group centre register can determine that the called party is not directly accessible from the originating exchange, no attempt is of course made to callback to that exchange but the connection is set up through the group centre switching equipment. For a known length of number, a connection-complete signal // is sent to the originating exchange before the connection is routed to the called party. If the length of the number is unknown, the connection-complete signal can be sent only after the group centre has received information of the called party's line condition from the destination exchange. Use of local register REG-L If all junction circuits are engaged when the subscriber initiates a call, the local register (if installed) is seized. It transmits dial tone, receives digital information from the subscriber's dial and determines whether the call is external or local. In the former case it returns busy tone. If the subscriber does not replace, REG-L is time-released and the subscriber is placed on line-lockout. In the latter case (local call) REG-L connects via MIR-REG to the marker equipment, after which the selector stages are set up via a cord circuit SNR. Incoming calls On an incoming call on a junction circuit from the group centre the seizure signal causes a KM to be connected to FDR via FID. When KM has received complete information of the number, the marker equipment is seized and the SLD, SLC, SLB and SL stages are set up to the wanted subscriber's line. KM sends a B-controlling signal (free, engaged, intercepted) back to the sending register and thereupon releases. If the subscriber is free, ringing signals and ringing tone are sent from FDR and, on answer, FDR is through-connected and returns an answer signal backward. If the subscriber is engaged or intercepted, the clearing of the equipment is effected from the originating group centre. Mechanical Design The equipment is mounted on racks 00 mm (' 0") high, mm (' ") wide and 0 mm (' ") deep (for two-sided racks). ll units, both switches and relay sets are connected to the racks by plug and jack. Typical floor layouts are shown in fig..

13 Group Centre Type RK Type RK is designed for group centres and is a development of the terminal exchange type RK, supplemented by transiting facilities with sending registers and with equipment for route and tariff determination. The subscriber lines are connected in line groups of 00 lines in the same way as in type RK. The junction circuits terminate on the SLB-NE stage; each junction line group consists of 0 or 0 SLB-NE verticals for 0 junction circuits (fig, ). line group thus serves either 00 subscriber lines or 0 junction lines. The system is designed for a maximum of 0 line groups, but whether or not this maximum capacity can be utilized depends on the traffic load on the marker equipment. ccording to its size the exchange contains a number of line groups terminating on the SLC stage, which in turn may be connected to an SLD stage. On the verticals of the SLC (SLD) stage terminate cord circuits SNR, relay sets FDR for two-way junctions (or FIR for incoming and FUR for outgoing), and registers REG. If there is an SLD stage, one side of SNR and one of the register links is connected to SLC verticals. The switching functions within the SL and SLB stages are performed by markers BM. which can be connected to all line groups. n exchange can be equipped with one or two BM operating simultaneously in different line groups. The SLC and SLD stages also comprise C and D markers (CM and DM), which must be duplicated if the exchange has two BM. Duplicated CM and DM can connect simultaneously to their respective SLC and SLD selectors. Outgoing junctions to terminal exchanges, group and zone centres terminate both on the SLB-NE multiple and on the verticals of the last selector stage (SLC or SLD). Incoming junctions from another group centre or from the zone centre, however, terminate solely on the SLC (or SLD) stage. The registers receive decadic digital information from subscribers both on the home exchange and on connected terminal exchanges. Via a finder KSS the registers have access to code senders KS for MFC signalling. -k Line groups Group or zone centre -0 Line groups y-tm P* P* \ SLC SLD \SNR I Group or zone centre Fig. x Trunking diagrams for group centre RK Line group for 00 subscribers: 0 SL and 0 SLB verticals Line group for 0 junction lines: 0 or 0 SLB- NE verticals Max. number of verticals: 00 SLC, 0 SLD CM DM \RBG (-J VM Y^-i r:rt KSS y-nn * 000

14 Code receivers KM with facilities for storage and translation can be connected direct to junction circuits from group and zone centres if the numerical information is received in MFC for connection through the home exchange without being transmitted onward. To registers and code receivers are connected route markers VM which analyse the received number for route and tariff determination. VM is equipped for a total of 00 junctions (outgoing and two-way). There may be up to routes with three alternative choices (e.g. one direct and two alternative routes). The number of circuits per route is limited only by the number of available SLC or SLD verticals and by the multiple capacity of SLB-NE. The subscribers" line group is made up in the same manner as in type RK, as already described. line group for 0 junctions is made up of one or two crossbar switches SLB-NE (fig. ). The crossbar switches for SLB-NE have 0 five-pole outlets per vertical. The SLB and SLB-NE verticals in the various line groups terminate on the multiple outlets in the SLC stage. For more than four line groups an SLD stage will be required, the multiple outlets of which connect to the SLC verticals. The crossbar switches in the SLC and SLD stages have 0 five-pole outlets per vertical. Fig. 0 shows an example of groupings for different sizes of exchange. The grading between SLC and SLB may be arranged so that either 0,,, or vertical in each SLB (SLB-NE) crossbar switch is accessible from a group of SLC crossbar switches with common multiple. The SLB (NE)ISLC and SLC/SLD links pass through an I.D.F., so allowing the groupings and the number of SLC and SLD switches to be adapted to the actual requirements. Switching Units and Their Functions The block diagram in fig. shows in main outline the switching equipment of RK. Part of the equipment is similar to that of RK but is included here to complete the picture. B connector (MIR-B): is associated with a specific line group for max. 00 subscriber lines and connects a free marker to the subscriber line equipments LR and selectors SL/SLB of that line group. Each installed line group for 00 subscribers requires one MIR-B unit. B connector (MR-B): is associated with a specific line group for max. 0 junctions to terminal exchanges, other group centres and zone centre. MIR-B connects a free marker to the junction equipments EDR, FIR, FUR and selectors SLB-NE of that line group. Every installed line group requires one MIR-B unit. n exchange can be equipped with a maximum of 0 MIR-B together. and MlR B B marker (BM): controls the line groups (SL/SLB and SLB-NE stages). The system can be equipped with a maximum of two BM. C marker (CM): controls the SLC stage, which can contain a maximum of 00 verticals, the number of CM being limited to two. D marker (DM): controls the SLD stage with max. 0 verticals. maximum of two DM can be installed. Marker connector (MIR-REG): connects the marker equipment to registers REG and route marker VM. There are also bypaths from MIR-REG to various units, such as cord circuits SNR and junction circuits FDR, FUR. FIR.

15 00 subscriber lines Line -i r 0 o SL o -o -o -o -o -o -o -o-o-o -o -o-o O O-O O group SLB 0 junction lines SLB-NE oo-o-oooo-o-oo] / -o-o-o-o-o-o-o-o-o-o -o-o-o-o-o-o-o-o-o-o [o-o-o -o o-o -o-o-o-o if -o-o-o-o-o-o-o-o-o-oj S (oo-o-oo-ooo-o-o] S J ' SNR,REG,FDR SLC Line group SL and junction lines It t t i i. o-o-o-oo-o-o-o-o-o-]o-o-o-o-o-o-o-o-o-o- SLB(-NE) line groups line groups -oo-o-o-o-o-o-oo-o ^ooo-oo-o-o-ooo ^o-o-o-o-o-o-o-o-o-o LOOO-O-O-O-O-O-O-O }o-o-o-o-o-o-o-o-o-o -o-o-oo-o-o-oo-o-o l-o-o-o-o-o-o-o-o-o-o] ^o-o-o-o-o-o-o-o-o-o fo-oo-o-o-o-q-o-o-oj }-o-o-o-o-o-o-o-o-o-o ( ^ j-o-o-o-o-o-o-o-o-o SNR,REG,FDR / * s e SLC s to II SL and junction lines SL and junction lines I! ~ " Line group I 0 line groups SLB(-NE) SLD -o-o-o-o-o-o-o-o -o-o o o -o-o-o -o o-o-o-o -QO-O-O-OO-OO-O-O o-o-o-o-o-oo-o -oo I-Q -O -O-O -O -O -O -O -O-O oo-o-o-o-o-o-o-o-o O-OO-O-O-Q-OO-GO -o-oo-oo-o-o-oo o fo-o-o-o-o-o-o-o-oo o-o-o-o-o-oo-oo o I J V S T 0 It I * IS SLC. tt REG SNR REG FDR Line group t t SLB(-NEJ 0 line groups SLD OO-O-OO-O-Q-O-O-O o-o-o-oo o-o-o-oo -O-O-O-O-O-O-O-O-O-O O-OO-O-O O-O-O-O-O -OO-O-O-O-O-OO-O-O O-O-O-O-O-O-OO-O-O -o-o-o-o-o-o-o-o-oo -o-oo-o-o-o-oo-o-o -o-oo-o-o-o-o-o-oo -o-oo-o-oo-o-o-oo o-oo-o-o-oo-o-o-o OO-O-O-OO-Q-OOO O-O-OO-OO-O-OO-Q oo-oo-o-o-o-o-o-o ooooo-o-o-o-o-o oo-o-oo-o-o-o-oo -oooo-o-o-oo-o-o -oo-o-o-o-o-ooo-o i ' <".? V '0 u S «ii.'v s i >! II IB 0 ^<, "islc SNR REG FDR Fig. 0 Grouping plans for RK x

16 GROUP CENTRE JUNCTION CCT. WITH OECD/C NUMBER TRNSMISSION I LINE OROUPNoX Fig. X Block diagram for group centre RK Eight registers can be connected to one MIR-REG and the system can be equipped with a maximum of three MIR-REG. The number of MIR-REG required is determined partly by the traffic load they are to carry and partly by the number of registers. It should be noted that the total number of MIR- REG and code receivers KM (for connection to junction circuits) is limited to six. Register (REG): stores the received digital information from subscribers on the home group centre or connected terminal exchanges. REG can also receive digital information from another register or transmitting unit, from another exchange in the form of decadic pulses, or from an operator. REG sends on the outgoing junction the information required for setting up the connection, and releases as soon as the connection is completed. Code sender (KS): is connected via sender-finders KSS to a register when MFC signalling is required. Each KS has access to six-frequency generators and contains a four-frequency channel signal receiver (controlling signals). Code receiver (KM): can be connected via receiver-finders KMS if the register is to receive digital information in MFC. Each KM contains a signal receiver for six frequencies and has access to four-frequency generators (controlling signals). Code receiver-connector (FID): connects the junction relay sets FDR and FIR to the code receivers KM (see below). Each FID unit has a capacity of five junction circuits and two KM, and connects one of the five circuits to a KM. Code receiver (KM) with storage and translation facilities: can be connected via connector FID to junction circuits FDR and FIR used for MFC signalling alone, if the digital information received by KM is to be used solely for operation of the exchange's own selector stages and is not to be transmitted onward.

17 Register-finder (RS): connects an incoming junction to the register and is used if decadic signalling is employed on that junction. RS connects a register in the interval between two digits. n RS unit has a capacity of 0 junctions and registers. Route marker and analyser (VM): handles the digital information received from registers or code receivers. fter analysis of the received digits VM can decide: the route and junction the tariff the length of number, to which connection is required. VM is designed for a total of routes and 00 junctions (two-way plus outgoing) with three alternative choices (e.g. one direct and two alternative routes). When VM has found a free circuit, it informs REG of the method of signalling the digital information (MFC or decadic) and the first digit to be sent. It also calls the marker equipments, after which the selector stages are set up. to be applied on the connection. This information is sent by VM to REG and thence forwarded via a bypath to the junction relay set, where a corresponding combination of tariff relays operates. i.e. the number of digits in the called subscriber's number. The information is transmitted from VM to REG. If the analyser cannot determine the length of the number, the information "unknown length of number" is sent to REG. If REG can itself determine the length of the number, the information from VM is of course unnecessary. In addition to these particulars, the analyser can supply information to the effect that, for example, the number is barred to certain categories of subscribers the number belongs to an unallocated 00-group (as a rule only within the home group area). Sometimes it may be desirable to obtain information of the route at as early a stage as possible, e. g. for setting up a connection to a decadic exchange system. In such case REG calls VM after only one or two digits. But these digits may not suffice for information of tariff and length of number, in which case REG must call back VM and obtain the missing information. It can call VM three times. Switching Processes Call originating from group centre On a call from a subscriber, a free BM connects to LR via MIR-B, identifies the calling subscriber's position in the SL multiple and ascertains his category. With the aid of BM and CM the SL. SLB and SLC stages are connected to a free register REG. The subscriber category is transmitted to REG and stored by it, after which dial tone is returned to the subscriber. The register receives the digital information from the subscriber and, if necessary, calls the route marker VM. which analyses the number. If the called party is on the same exchange (i.e. the group centre) as the calling subscriber, a local connection will be set up when REG has received full information of the number. REG calls a free BM and transmits to it the necessary portion of the called subscriber's number. BM ascertains whether the called line is free and, in such case, sets up a connection from it to a free cord circuit SNR via SL. SLB and SLC. From REG a signal is sent via SLC, SLB and SL to the calling subscriber's line equipment, placing a marking condition on it. after which this switching path

18 and REG are released. The marker sets up a new connection between the calling subscriber's line and the previously selected cord circuit SNR. after which the marker releases. The subscribers' lines are now interconnected and ringing signals and ringing tone are sent from SNR. If the called party is engaged or intercepted, BM signals the condition to REG and thereupon releases. Busy or interception tone is returned to the calling subscriber from REG. If the subscriber does not replace. REG is timereleased and the subscriber is placed on line lock-out and receives busy tone from his line equipment. In the case of an intercepted line, the connection may be rerouted to an interception operator. If the called party is on a terminal exchange in the group area, a connection must be set up through the centre from the calling subscriber's line to a junction circuit FDR-E. When REG has received full information of the number, the route marker VM is called and selects a free line to the destination exchange, after which VM releases. BM. CM and DM set up a connection from REG via SLD. SLC and SLB-NE to the selected junction circuit FDR-E. code sender KS is connected to REG via KSS. The digits required for directing the selector stages in the destination exchange are sent by MFC from the group centre. connection-complete signal from the destination exchange is received by KS and transmitted to REG. after which KS releases. If the called party is free, REG sends a signal via the selector stages both to the calling subscriber's line equipment LR and to FDR-E, placing a marking condition on these equipments, after which REG and the switching paths to REG are released. The marker equipments set up a new connection between LR and FDR-E via SL. SLB. SLC and SLD. If the called party is engaged or intercepted, the connection with the destination exchange is cleared and a tone is sent to the calling subscriber from REG in the manner already described. In the case of an intercepted line the connection may be rerouted to an operator. If the call has to pass through another group centre or the zone centre, the process is the same as on a call to a terminal exchange, with the exception that a junction circuit FDR-N is used instead of FDR E. Call originating from a terminal exchange On a call from a terminal exchange, a free BM connects to FDR-E via MIR B and identifies the position of the line in the SLB-NE multiple. With the aid of BM and CM a connection is set up through the SLB-NE and SLC stages to a free register REG. The digital information is received by the register and, if necessary, the route marker VM is called for analysis of the number. Call-back to the originating terminal exchange, if required, is done in the usual manner. For a local connection in a terminal exchange, the connection is set up by the terminal exchange code receiver after reception of the number. lunction circuit, register and selectors are released in the group centre on reception of a line-free signal from the originating exchange. If the call is to another terminal exchange in the group area, VM is seized after the call-back, analyses the number and selects a free junction circuit FDR-E to the destination exchange. BM. CM and DM set up a connection between the selected FDR-E via SLB-NE. SLC. SLD and the register. code sender is connected to REG via KSS and the digital information is sent by MFC to the called exchange. The end-of-selection signal from the called exchange is received by KS and transmitted to REG, after which KS releases. If the called party is free, REG sends a signal via the selector stages to both FDR-E units, placing a marking condition on them, after which these switching paths and REG are released. The marker equipment sets up a new connection FDR-E. SLB-NE. SLC. SLD, FDR-E.

19 If the called subscriber is on the group centre, the marker BM is called after VM has analysed the number. The necessary digits are sent to BM from REG. BM ascertains whether the called line is free and, if so, REG sends a signal via the selector stages to the calling FDR-E, placing a marking condition on it, after which this switching path and REG are released. The marker equipment sets up a new connection between FDR-E and the called subscriber via the SLD, SLC. SLB and SL stages. If the call must pass through another group centre or the zone centre, the procedure is the same as on a call to a terminal exchange, with the exception that a junction circuit FDR-N is used instead of FDR-E. Incoming call from zone centre or other group centre On an incoming call from the zone centre or another group centre on circuits with MFC" signalling, a code receiver KM is connected to the junction relay set FDR-N via connector FID. The numerical information is sent from the originating register by MFC and received by KM. If the called subscriber is on the group centre, KM requests from the originating register the remaining digital information and transmits it to BM. If the subscriber's line is free, a switching path is established from FDR-N to it via the SLD. SLC. SLB and SL stages. n D -D D 00 subscriber lines junction lines Fig. Floor layouts for group centre RK Rack x SL, SLB and line equipment, 00 subscribers' lines Marker equipment Tariff equipment and MIR-REG Code senders SLC, SLD, SLB-NE crossbar switches with markers SLC, SLD crossbar switches SLB-NE crossbar switches with connecting relay sets Registers Cord circuits and code receivers 0 Junction circuits MK I.D.F. KK M.D.F. B Battery IT Rectifier SM Subscriber's meters Rack height: 00 mm (' 0") Free ceiling height: 000 mm (' 0") 00 subscriber lines junction lines 00 subscriber lines 0 junction lines

20 If the subscriber is on a terminal exchange, KM calls the route marker VM after receiving a sufficient number of digits for identification of the called exchange. VM analyses the number and selects a free junction FDR-E to the called exchange, after which VM releases. connection is set up to this junction from FDR-N through the SLD. SLC and SLB-NE stages, after which the code receiver is disconnected after, if necessary, having sent a suitable controlling signal. The remaining digital information is sent from the originating register direct to the destination exchange. Mechanical Design The equipment is placed on racks 00 mm (' 0") high, mm (' ") wide and 0 mm (' ") deep (for two-sided racks). ll units, both switches and relay sets, are connected to the rack by plug and jack. Floor layouts are shown in fig.. Group Centre with Transit Stage Fig. shows a trunking diagram for a group centre made up of a terminal exchange RK and a transit exchange RM 0. The dashed lines show how the local section can be extended beyond the maximum capacity of 000 lines of the RK system by adding an exchange unit of this capacity, so increasing the capacity of the local equipment to 000 subscriber lines. By using the direct route facility in RK. connections between the two 000- line units can be passed direct through FDR-L links (which may be unidirectional) so that the transit exchange need only be loaded with such traffic when all FDR-L are engaged. The switching procedure in this type of group centre does not differ essentially from that already described for RK. When a call is initiated, a link Local exchange RKI Fig. x Trunking diagram for group centre made up of a terminal exchange RK and a transit exchange RM 0

21 RK SL SL {TERMINL EXCHNGE " \ REGL ) p ^ \ --V C M?KH p I \u C r»"l I {' ' i "Vs -^w TERM IN L EXCHNGE 0-C 'H^H I Zone centre Term/no e/cftonoe urnvtcentre! <: () Group centre * i;/ie concentrator SW LS SiC HHH =^H~./. SIC SIP T ^ J., owrj <HHH ^ ^sg GV GVB r=e ^ rfgw//l EXCHNGE f*w [f pg flr= ^g= CENTRE [ C- l J V o w X gs - r J, ml <H)-E IOK^> SM i-s LC N-TT^SC {TERMINL EXCHNGE [ ] - «esj] Irpg-fj RK ^ ^ ^ j ±? Si./ SL SLC H»«EXCHNGE lr.»<[ fi H^jf 0 \RKSi SL SLB L- SL-HE { EFT} ioh^n- ^ i - -i GffOOP CENTRE OEr-0 N ^fc-rt] [vny^ L ^ GTOOP CENTRE KSS EK -0 Fig. x Zone area with systems RK 0, RM 0 and RL 0

22 FURL is seized to the transit exchange, where a register is connected. Transmission of category to register, call-back to local exchange and all other functions are similar to those in an ordinary terminal exchange. Example of Use of System RK 0 n example of the use of system RK 0 for automatization of a zone is shown in fig.. The zone has three group centres and a zone centre and is thus divided into four areas with terminal exchanges. The zone centre () is made up of a local exchange RK and a transit exchange RM 0, which handles all traffic between the exchanges in the zone and other zones. Terminal exchanges B and C of type RK are connected to the zone centre. Group centre D of type RK with terminal exchanges E and F (RK and ) and group centre G of type RK with terminal exchange H of type RK have junctions to the zone centre. There are no junctions to the zone centre, however, from group centre J (RK ), the latter being connected to exchange G. which accordingly serves as transit centre for traffic from and to exchange / and its terminal exchange K (RK ). There are direct routes between D and C and between B and H. Exchanges B and G have line concentrators RL 0 which serve subscriber groups within these exchange areas. MFC signalling, on the principles already described, is employed between the exchanges in the zone area and to other zone areas. In the example shown it is assumed that, for incoming traffic from other zones, the zone centre has a register REG-Y with access to a code receiver KM for receipt of MFC digital information. The connection within the zone is thereafter controlled in MFC by REG-Y. This arrangement means that registers and route markers need only know the numbering within their own zone.

23 ' - Crossbar Private utomatic Branch Exchanges (P..B.X.) for 0 and Extensions W DENSTEDT, TELEFONKTIEBOLGET LM ERICSSON, STOCKHOL M UDC.. LME, The high reliability and rapidity of the crossbar switch has made it one of the most important components both in public and private exchanges. Telefonaktiebolagei L M Ericsson has employed this switch in its 0-line and -line private automatic branch exchanges. These exchanges are typed RD 0 and RD. The RD 0 and RD private automatic branch exchanges have a high traffic handling capacity, require little maintenance and offer a number of traffic facilities. They are simple to install and, being very silent in operation and requiring little space, they can even be placed on an office wall. Normal telephone sets with push button are used as extension and operator instruments. RD 0 (fig. ) is equipped for 0 extensions. exchange lines and connecting circuits for internal calls. RD (figs.. and ) has a capacity of extensions. exchange lines and connecting circuits for internal calls. X 0 X Fig. P..B.X. RD 0, (left) with front cover removed and (right) with frame swung out The fact that the connecting circuits are never employed for setting up external calls, or for enquiry and transfer, ensures maximum utilization both of exchange lines and connecting circuits.,fi ram a-m tm tm am \hmik «is ' %M ii m ii '.a im m mm dm d- s ~v~ >* ' aaru/.jri i< si s» im IJ a a >hm a z u?,m n sni a «.gj! ; a «sa &;a is-s ~~ < ~wrii, $ $-. ' * '"- '--- :--. ~*j%~> : im& -fimfa ffcs- ' $ '. - -"" H&jr >^ e^>^^^^^f^^nmnn^ I'

24 Traffic Facilities In addition to the usual facilities such as dialled internal and external calls, outgoing calls via operator and operator handling of incoming calls, a modern switchboard must offer various other services in order to be an effective aid in a modern organization. For this reason the RD 0 and RD exchanges have been equipped with the following facilities. utomatic enquiry to another extension during external calls without the public subscriber being able to overhear the conversation. utomatic transfer of an external call from one extension to another. call can be transferred any number of times. utomatic camp-on position. When the operator or an extension attempts to transfer a call to an engaged extension, the call can be put on the camp-on position. If the called party becomes free within 0 seconds, the call is put through automatically. Otherwise the operator is automatically recalled. This means that a public subscriber can never be forgotten a mark of good telephone service. Recall of operator if an extension fails to answer within 0 seconds. Fig. P..B.X. RD Parking of external calls. If the operator is engaged on an external call when a new external call arrives, she hears ringing tone in her receiver. She can then park the previous call in order to deal with the new call. If this takes her more than 0 seconds, the parked connection transmits a ringing tone to the operator to remind her that it is waiting. *\F aaaaaaau SPPPPWP,*II*IIIW#^ Priority can be granted to any extension by simple strapping in the switchboard. priority extension can enter an engaged circuit by dialling an extra digit after receipt of busy tone. ticking tone is then transmitted to the conversing parties to warn them that a third party is on the line. Restricted service can be arranged for any number of extensions. The P..B.X. has split feed transmission bridge for internal calls. On external calls the feed comes from the P..B.X., which is thus independent of the current feed system of the public exchange. The P..B.X. is designed for first-party release, which means that an extension is free for a new call as soon as he has replaced his handset. Under night service conditions incoming calls are automatically redirected from the operator's telephone to another extension. On mains failure the exchange lines are automatically switched through to predetermined extensions. Fig. RD with front cover removed The switchboard incorporates line-lock-out arrangements, which implies that false signals caused by a line fault or failure to replace a handset cause automatic release of the register. The line is switched over to its cut-off relay until the fault has been remedied. s the line is thereby locked-off from the switching equipment, the traffic handling capacity of the P..B.X. is unaffected. 0

25 ll these functions have been introduced as standard facilities in the switchboards. In addition, the following extra equipment can be supplied: Lamp panel on which the operator can immediately see which extensions are engaged. Sequence call equipment which is used when an external call has to be switched successively to several extensions. Meters for external calls can he installed in areas where the public exchange is equipped for connection of subscribers' meters on the subscribers' premises. The meters can be connected either to each individual extension or to the exchange lines. In the latter case they are placed in an auxiliary box beside the operator. Trunk discrimination for all or certain extensions when individual metering is not required. The trunk discrimination may be effected by a digit counter, which means that if more digits are dialled than correspond to a local call the connection is broken down. When connected to public exchanges giving reversal of polarity on trunk calls (as, for example, in L M Ericsson's public exchanges of type RF 0), discrimination can be arranged by the introduction of rectifiers in the exchange line loop. Mechanical Design The components crossbar switches, relays, capacitors etc. are of the same design and high quality as in L M Ericsson's public exchanges. They are mounted on a wall rack with hinged frame as shown in figs. and. The entire frame is enclosed under a cover. Owing to the accessibility of the various components and the small dimensions of the frame, these switchboards are permanently wired in the factory. The dimensions of the switchboard are RD 0: height mm, depth 0 mm, width 0 mm. RD : height 00 mm, depth 0 mm, width 0 mm. t the bottom of the frame are strapping terminal blocks for priority and other special facilities, M.D.F. and fuses. The M.D.F. of RD 0 accommodates 0 and, of RD, 0 extension lines. ll parts are designed to withstand tropical conditions. Plastic-insulated wire is used throughout. Power Equipment The required operating voltage, V, can be obtained either from a battery and charging unit or from a battery eliminator. In places where there is little risk of mains failure, a battery eliminator is undoubtedly preferable. It occupies little space and requires no maintenance. suitable battery eliminator for these switchboards is BMN (fig. ) which delivers a voltage of V and a maximum current of. The unit has tappings for 0, 0 and 0 V, 0-0 c/s. The 0 V ringing voltage is obtained from an extra winding on the unit's transformer. The tones, of frequency c/s, are obtained from a transistor equipment fitted in the switchboard.

26 Internal Calls The extension numbering scheme for the 0-line switchboard is -, 0 and for the -line switchboard -, -. When an extension raises his handset, he is connected via LR/BR to REG (fig. ). Dial tone is returned and he dials the wanted number. If he does not commence dialling within about seconds or, if the time between the first and second digits exceeds seconds, REG is released and busy tone is returned to the extension via LR/BR. On completion of dialling, REG investigates the condition of the called extension^ line and the availability of a free connecting circuit. If the called extension is free and there is a free connecting circuit, the connection is set up via verticals a and b, after which REG releases and the first ringing signal is transmitted. Thereafter intermittent ringing signals are sent from the connecting circuit. t the same time the caller hears ringing tone. When the call is answered, the ringing discontinues and communication is established. If the called party is engaged or if there is no free connecting circuit, the register releases and the caller receives busy tone via LR BR. If a priority extension calls an engaged extension, a preliminary connection is set up via a free connecting circuit, after which the register releases. The caller can now enter the engaged circuit by dialling one digit. ticking tone is sent to the conversing parties to indicate that a third party is on the line. When the priority extension replaces his handset after having presented his message, the ticking tone ceases. The fact that these exchanges arc designed for first-party release means that an extension becomes free as soon as he has replaced his handset. Fig. Bittery eliminator BMN (bjlcw) with cover removed X X Incoming Calls from the Public Exchange On incoming calls from the public exchange the signal is recorded by FDR and forwarded to the operator's telephone via vertical c. If the operator's line is free she hears intermittent signals. If her line is engaged a ringing tone is issued to indicate that a call is waiting. s soon as she has dealt with the previous call, the waiting call is put through and her telephone is rung. When she answers the call, the ringing signals are cut off and communication is established. To extend an incoming call, the operator momentarily presses the push button on her telephone. The transfer contact F in FDR is thereby actuated and connection is made with REG via a bypath. The operator dials the digits of the wanted extension, after which REG sets up the connection to the latter via vertical d. If the operator is not to announce the call, she can now leave the connection by simply replacing her handset. x Fig. Switching procedure LR BR Line and cut-off relay REG Register SNR Connecting circuit for internal calls FDR Exchange line equipment SLV Finder and final selector CL Exchange line a d Verticals of crossbar switch If the called extension does not answer within 0 seconds, the operator is recalled. If the line is engaged, the operator can either place the call on the automatic camp-on position or. by dialling an extra digit, can enter the engaged circuit. This she can do regardless of whether the extension is engaged on an external or internal call. s long as the operator is on the line a ticking tone is transmitted. fter announcing the call she can simply replace her handset. The incoming call now waits for 0 seconds and, if the extension becomes free during that time, it is put through and the extension is rung. Otherwise the operator is recalled.

27 Outgoing Calls to the Public Exchange The extension raises his handset and is connected to the register. On return of dial tone form the register the extension momentarily presses the push button on his telephone. REG now connects the extension to a free FDR via vertical c and then releases. The extension receives dial tone from the public exchange and can dial the wanted number. If all FDR are engaged, REG releases and the extension receives busy tone via LR/BR. Enquiry Calls If an extension wishes to consult another extension in the course of an external call, he momentarily presses the push button on his instrument. This connects him to vertical d via transfer contact F in FDR. t the same time connection is established with REG via a bypath and the extension hears dial tone. When REG has received the digits of the called extension's number, vertical d is connected to the called extension and REG releases. Communication is established as soon as the extension answers. The external subscriber is thereby isolated and cannot overhear the conversation. The enquiring extension can now switch backward and forward between the external and internal connections by pressing his push button. The connection via vertical d is restored as soon as the enquiree has replaced his handset. Transfer Should an extension wish to transfer an external call to another extension, the procedure is the same as on an enquiry call. fter dialling the wanted number, the calling extension replaces his handset. He need not wait until the called extension answers. When the calling extension has replaced his handset, his line is cleared via vertical c, and contact E switches over. When the called party answers, he is connected to the external subscriber via contact E in actuated position. If the called line is engaged, the calling extension, if he possesses priority facilities, can enter the circuit and announce the call before replacing his handset. The external call is then placed on the camp-on position. s soon as the called extension becomes free, the call is put through. If the latter does not become free within 0 seconds, the operator is called. Installation and Maintenance These switchboards, with their small dimensions and permanent wiring, are very simple to install, since the hinged frame with all switching units is set up after the backplate has been erected on the wall. The supply cable and the extension and exchange lines terminate on easily accessible terminal blocks. fter strapping of restricted, priority and night service extensions has been effected in accordance with the customer's desires, the installation tests are carried out. It thereafter remains simply to complete the jumpering and the switchboard is ready for use. Switchboards with mechanically driven selectors require preventive maintenance at regular intervals if they are to function reliably. For crossbar switchboards this preventive maintenance is superfluous. They therefore cost less in maintenance than other types of switchboard. The lines between extensions and switchboard consist of two wires and an earth return wire which may be common to all extensions.

28 Technical Data Operating voltage The operating voltage for these switchboards is V, but voltage fluctuations between and 0 V can be admitted without jeopardizing their operation. Line data The resistance of extension lines may be as high as 00 ohms, including the telephone instrument. The leakage resistance between the two legs of a line or between a line leg and earth may be as low as,000 ohms. The line resistance between the push button and the positive terminal may be 00 ohms. The line and leakage resistances of the exchange lines depend on the performance of the public exchange. Feed The feed coils have a resistance of X 00 ohms, which can be adjusted to X 0 ohms. ttenuation The switchboard attenuation on internal calls is max. db and on external calls db, measured between 00 and 00 c/s. The crosstalk attenuation, also measured between 00 and 00 c/s, is above 0 db. Psophometric noise Noise caused by hum from a battery eliminator and crosstalk from tone- and ringing signals does not exceed mv on internal and 0. mv on external culls. Main Features of P..B.X. Types RD 0 and RD. High traffic handling capacity. Practically no maintenance. Silent operation. utomatic enquiry and transfer facilities. utomatic camp-on position. Priority facilities. Night service facilities. Line lock-out. Wall mounting 0. Supply via battery eliminator or via battery with automatic charger

29 LM Ericsson Exchanges Cut into Service CITY EXCHNGES Public exchanges with 00-line selectors Town E x c h a n g e Number of lines Town E x c h a n g e Number of lines Bolivia La Paz Brazil Campo Grande Curvelo Divinopolis Fortaleza Jundiai Maringa Uberaba Colombia rmenia Bogota DE» Calarca Medellin area»»»» Neiva Popayan Calacoto Centre Centre Chapinero merica Bosque Poblado C C Catanzaro Cava dei Tirreni Formia Gaeta Messina Napoli/Naples»»» Palermo»»»» Pompei Reggio Calabria Rossano Calabro Salerno S. Giuseppe V. Sorrento Taranto Torre del Greco Vibo Valentia medeo Capodimonte Nolana Vomero III Calatafimi Ferrovia Mondello Polacchi S. Lorenzo Ecuador Guayaquil»» Quito»» Finland Jyvaskyla Italy North Italy Chioggia Dolo Legnago Mogliano Padova Schio Thiene Venezia/Venice Verona Vicenza Centro Sur Urdesa Centro Inaquito Mariscal S jcre Murano Lebanon Beirut» Mexico Cuernavaca Durango Mazatlan Mexico D. F.»»»»»»»» Oaxaca Toluca Netherlands Rotterdam Dora Furn elchebak Morales Peralvillo Piedad Portales Sabino Tacuba Valle Victoria Zocalo Schiedam South Italy Barcellona Bari Catania Catania-Ognina Netherlands' West Indies Curasao»» Brievengat Dokterstuin Otrabanda

30 Town Exch a n g e Number of lines Panama David Panama City Panama Interior from the 00-line Ericsson 00-selector exchange Yenimahalle, nkara, Turkey. Sweden Falkoping Gavle Goteborg/Gothenburg Centrum rea» Suburban rea»» Halsingborg Jakobsberg Kristianstad Lidkoping Stockholm Centrum rea» Suburban rea»»» Solvesborg Trollhattan Ostersund Gruppstation Orgryte Biskopsgarden Partille Savedalen Gruppstationer Ostermalm Djursholm Farsta Hasselby Viggbyholm Town Norway Kristiansund N Notodden Porsgrunn Sandnes Skien Sulitjelma Trondheim Exchange Number of lines Turkey Canakkale Elazig Giresun Maras Ordu Rize Urfa Venezuela Barquisimeto Total Public exchanges with crossbar switches Town Exchange Number of lines Town Exchange Number of lines Brazil Barbacena Fortaleza Guaratingueta Guarulhos Pirassununga Santo ndre area»» B. Menezes Ribeirao Pires Santo ndre Sao Bernardo Santo ndre area Sao Joao da Boa Vista Burma Rangoon Colombia Bogota DE Republic of Congo Pointe-Noire Sao Caetano Tamwe Chico

31 Town Exchange Number of lines Town Exchange Number of lines Denmark arhus» Esbjerg Frederikshavn Grenaa Hobro Ikast K.0benhavn/Copenhagen»»»»»»»»»»»»»»»»» Nsstved Odense Brabrand Syd Bagsva:rd Ballerup Bella Borups lle Br0ndby0ster Dams0 Glostrup Herlev Hundige Hvidovre Lyngby Nora Ryvang R0dovre Sundby0ster S0borg Taastrup Valby (extension; Helsinki/Helsingfors»»»» Kokkola/Gamlakarleby Langinkoski Martinmaki Niirala Oulo/Uleaborg Tuira Valkeakoski France Cognac Grasse La Chapelle St.- Mesmin Tulle Italy North Italy Piove di Sacco Treviso Venezia/Venice Herttoniemi/Hertonas Kaarela/Karbole Keskusta/Centrum Kulosaari/Brandb Sornainen/Sornas Mestre Finland Helsinki/Helsingfors Haaga/Haga 00 South Italy ltamura ugusta These exchanges, system CP 00, were delivered by Societe des Telephones Ericsson, Colombes. Interior from 000-line exchange at Ijsselmonde, one of the Ericsson crossbar exchanges at Rotterdam, Netherlands. x

32 Town Exchange Number of lines Town Exchange Number of lines South Italy (com.) versa Bisceglie Cefalu Fasano Gioia del Colle Ischia Marsala Martina Franca Nicastro Nocera Inferiore Nola Ottaviano Trapani Lebanon ley Libya El Beida Republic of Malagasy Majunga Mexico Mexico D. F.» Netherlands Barendrecht Capelle Santa Clara Tlalnepantla C Rotterdam» Sliedrecht Republic of Niger Niamey Sweden Karlskrona Nykbping Ronneby Sunne Tunisia Kasbah-G US Durham, North Carolina Galion, Ohio Live Oak, Florida Yugo-Slavia Beograd» Novi Sad Sibenik Zagreb» Ijsselmonde Schiedam (extension; kademija Tosin Bunar Novi Sad I Tresnjevka Trnje Total RURL EXCHNGES TRNSIT EXCHNGES Number Number of lines Number of junctions Public rural exchanges with crossbar switches, system RK, RT Finland Italy Mexico Netherlands Sweden US* Yugo-Slavia Total Rural exchanges with -, - or 00-line selectors, system OL, XY Norway Transit exchanges with crossbar system RK. RM Colombia Denmark Finland Italy Lebanon Mexico Netherlands Panama switches, This exchange, system CP 00, were delivered by Societe des Telephones Ericsson, Colombes. These exchanges, system NX-], were delivered by North Electric Co., Galion, Ohio. The equipment for these exchanges has been manufactured on LM Ericsson-license by the Yugo-Slavian factory Nicola Tesla, Zagreb. The number of lines includes both new exchanges and extensions of existing exchanges. These exchanges, system NX-, were delivered by North Electric Co., Galion, Ohio. Does not include junctions with 00-line selectors, system GF, cut into service in Sweden. Total

33 NEWS/rom ll Quarters of the World L M Ericsson Delivers dditional C.T.C. Equipment to Norwegian State Railways The Norwegian State Railways are to install C.T.C. on two lines, one in the north between Narvik and Riksgriinsen on the Swedish frontier, the other in the south between Stavanger and Egersund. The C.T.C. equipment is to be delivered by L M Ericsson's subsidiary company, /S Norsk Signalindustri, which had earlier installed the local signalling plants on these lines. The Norwegian State Railways have had experience of C.T.C. since, on the short Lierasen-Spikkestad line, with Lierasen, an unattended station, controlled from Spikkestad. The equipment for this installation was also supplied by L M Ericsson and Norsk Signal Industri. The Riksgransen-Narvik line is the Norwegian extension of the Swedish iron ore route from the Kiruna and Gallivare mines to the tlantic port of Narvik. Jt is a single-track line, miles in length, with four stations. The C.T.C. office is to be located at Narvik. Cooperation is planned between the Narvik office and the C.T.C. office at Kiruna, which controls the Riksgransen-Kiruna-Gallivare section, so that later on it will be possible to control right through to Narvik from the Kiruna office or up to the fourth station on the Swedish side from the Narvik office. The Stavanger-Egersund line is a single-track, -mile line with twelve stations controlled from the C.T.C. office in Stavanger. The Norwegian Railways have decided to employ the same C.T.C. system for these two installations as that supplied by L M Ericsson to the Swedish Railways, with a capacity of controls and indications per station. Some of the indications are transmitted only on special request from the C.T.C. office. The C.T.C. office will have keyboard control, and the track diagram, containing indication lamps alone, will be made up of standard sections with one section per station. Ermi's New Factory Opened in Karlskrona t the end of last year a highly modern factory was opened in Karlskrona, to which B Ermi, L M Ericsson's electricity meter company, has moved from Bromma, Stockholm. Ermi started operations in, but Ericsson has made electricity meters since. The new factory will allow a substantial increase in production capacity, which is at present about 00 electricity meters a day. Work on the Ermi factory started only in September 0. The company employs about 00 persons. Ermi is now a near neighbour of Ericsson's telephone factory in Karlskrona which, with its two branches at Ronneby and Olofstrom, has some 00 employees. n extension of the telephone factory is planned. The Chairman of the County Council, Thure ndersson, presided at the opening of Ermi's new factory in Karlskrona. He is seen here studying an Ermi electricity meter with transparent plastic cover. With him are the president of L M Ericsson, Sven Ture berg, and the head of Ermi, dolf Drougge. (Left) C.T.C. office, Kirura.

34 Knut Kaell in Knut Kaell died on February,, years of age. His death means the loss to the Swedish telephone industry of one of its pioneers. He had been associated with Telefonaktiebolaget L M Ericsson for nearly 0 years, from the time when he joined the company as a young university engineer until his retirement in. Memoriam Through Kaell's vigorous initiative as the work proceeded, he and his colleagues succeeded in creating the well-known Ericsson automatic system with 00-point switches. The first exchange to operate on this system was opened in in Rotterdam and was installed under Kaell's personal supervision. For some decades thereafter the 00 switch system remained the chief Ericsson product. The number of installed lines now exceeds h million. With his thorough engineering knowledge and his analytical frame of mind Kaell combined an integrity which commanded an immediate respect. His loyalty and readiness to help made him honoured and esteemed by all who came into contact with him. Knut Kaell's achievements in the service of telephone engineering and of our company have a permanent value. Sven T. berg the beginning of this year. Born in 0, he joined the Ericsson Group in 0. In he was appointed Director of Division at SIELTE and in Vice-President. In he was created Knight and in Commander of the Italian Order of Merit. Mr. Leveque succeeds Mr. Stefano Malerba who had been President of SIELTE since. Mr. Malerba was born in 0, joined the Ericsson Group in, became Director of Division at SIELTE in and Vice- President in. He is also Knight and Commander of the Italian Order of Merit. Mr. lberto O'Connor retired from the post of President of L M Ericsson's Spanish subsidiary, Compaiiia Espahola Ericsson S.., at his own request on November,. Mr. O'Connor will remain on the board of the company. The leadership of the company will be exercised by Mr. Carl-Erik Lindeberg, who has joined the board as chief executive officer. utomatic switching had captured his interest from the start. In the development of switching technique he saw the only means of providing for the rapidly growing need of telephone communication. In he was commissioned to work upon the basic ideas for an automatic telephone system with bare wire multiple which had been developed by xel Hultman at the Swedish Telecommunications dministration. New Head of SIELTE and Ericsson in Spain Mr. Umberto Leveque was appointed President of SIELTE, L M Ericsson's Italian sales company, as from (bove) The opening of the Pointe Noire exchange. (From left) M. Goura, M. de Pellegars-Malhortie and M. I'bbe Youlou in conversation with M. Farat. Ericsson ExchangeOpened in the Congo Republic The new automatic telephone exchange at Pointe Noire was recently opened by the President of the Congo Republic, M. I'bbe Fulbert Youlou, in the presence of M. Goura, Minister of Finance and Chairman of Office Equatorial des Postes et Telecommunications. M. Ibouanga, Minister of Industrial Production and of the P. & T. of the Congo Republic, and M. Farat, Chairman of Bureau d'etudes des Postes et Telecommunications d'outremer. 0 This, the first public crossbar exchange in West frica, was made and installed by Societe des Telephones Ericsson of Paris. It is a CP 00 system. The exchange is equipped for 00 lines with ultimate capacity of 000. The trunk office comprises positions with capacity of trunk lines. The exchange is the first of a series to be financed by Office Equatorial, and will be followed in by CP 00 exchanges at Port Gentil. Bangui, Fort-Lamy and Libreville.

35 «l t a celebration arranged at the Stockholm Town Hall on December last year employees of LM Ericsson were presented with gold medals accompanied by a gratuity. bove, left, Erik Fridzen and Karin Johansson, the male and female medallists with the longest years of service in the company, exchange congratulations. nother 00 office rooms are to be added to the Midsommarkransen block at the end of the year, by which time the new wing is expected to be complete. It will be storeys high with a total floor space of over sq.ft. The new wing runs out at right angles from the extension (above, right). n exhibition of L M Ericsson and Marconi products was opened at the end of last year at Lagos, capital of Nigeria, in conjunction with the starting up of the joint undertaking, Nigerian Telecommunications Corporation (NTC). s seen below, there were many young technicians keen to try out the Ericofon. Mr. R. Diks, Director of the Dutch P.T.T., and Mr. Badon-Ghijhen, Director of L M Ericsson's factory at Rijen, have been visitors at the main Ericsson factory in Stockholm. Mr. Badon-Ghijben is seen in the centre with Mr. Diks (in front of him) and Mr. Patricks of L M Ericsson (behind him). (Below) The Deputy Chief of the Swedish ir Force dministration, Major General Falk (left), and his Heads of Division, viewing a model of the main Ericsson factory in the course of a visit.

36 In Memoriam Georg Irming, chairman of Telefon Fabrik utomatic. Copenhagen, attended the annual staff gathering of the company on November., and spoke at the dinner, full of vitality, and with all his usual elegance and charm. Later in the evening he had a stroke and died suddenly. Ever since his retirement on pension from the post of Director of Telephones of the Copenhagen Telephone Company he has been chairman of the board of Telefon Fabrik utomatic. With his wise judgment and amicable nature he contributed actively to the fine spirit in the company and to the good relations on the board, both among its members and in its external relations with Danish and Swedish associates. Georg Irming was head of the Copenhagen Telephone Company when L M Ericsson received its first large order for the automatization of the Copenhagen network, which has been of such significance both for the building up of the Danish telephone system on modern principles and for L M Ericsson. ll of us who knew Georg Irming will feel the loss of a sterling character and a charming friend. Cornelius Berglund J.. R. Nielsen, Chief Engineer at the Copenhagen Telephone Company, must have felt happiness at the demonstrations of affection and esteem shown him during his recovery from a heart attack some years ago. ll of us who knew JRN were overjoyed when he returned from his illness, still the unfaltering fighter for his good ideas and the heartwarming, lively and considerate comrade. He was an able and pioneering technician who had a great influence on telephone developments in Denmark and beyond. His wise advice, given with good heart and a burning enthusiasm, was sought by many people from many countries. It was with great sorrow we heard that his intense vitality finally gave way before the second severe heart attack. We, the numberless friends of J.. R. Nielsen, shall be eternally thankful for all he so generously lavished upon us of his constructive mind, his rich experience, and of the goodness of his heart. Cornelius Berglund L M Ericsson at Montreal, Canada, is soon to have new office and storage accommodation. new building is being erected on the northern outskirts of Montreal. It will consist of two interconnected wings, one a two-storey office block and the other a single-storey stores building. Professor Edy Velander died on November., after a long illness. With him there went a frontranking figure in Swedish engineering research. Edy Velander's achievements were centred especially in his work as President of the Swedish cademy of Engineering Sciences. More than any other he laboured to establish the importance of research for technical progress. He successfully tackled every stratum of Swedish life the public, politicians and. not least, the leading men of industry. ll who had the advantage of intimate contact with Edy Velander were impressed by the breadth of his knowledge. His ability clearly and compellingly to describe complicated technical problems was unsurpassed in Swedish engineering circles. The chief impression, however, was of his enthusiasm for everything new, an enthusiasm which inspired both his immediate colleagues and those with whom he worked on the various committees of the cademy. Edy Velander was greatly interested in the advances made in telecommunications, and on the visits he made to our laboratories many of us had long discussions with him about what has been achieved and what we may expect for the future. The Ericsson Group has also directly benefited from his experience and knowledge through his membership of the boards of Ermi and RIF. L M Ericsson shares in the sorrow of the Swedish engineering world at his departure. Christian Jacobceus

37 UDC... LME BGER, R: Crossbar System RK 0 for Rural Exchanges, Exchange Types. Ericsson Rev. ():, pp.. The general principles of crossbar system RK 0 were outlined in Ericsson Review No.,. In this continuation of the previous article the various types of exchange covered by this system, RK and RK for terminal exchange, and RK for group centres, are presented. The article concludes with some examples of the use of the RK 0 system. UDC.. LME, DENSTEDT, W: Crossbar Private utomatic Branch Exchanges (P..B.X.) for 0 and Extensions. Ericsson Rev. ():, pp.. The high reliability and rapidity of the crossbar switch has made it one of the most important components both in public and private exchanges. Telefonaktiebolaget L M Ericsson has employed this switch in its newly designed 0-line and -line private automatic branch exchanges. These exchanges are typed RD 0 and RD.

38 The Ericsson Group ssociated and co-operating enterprises EUROPE Denmark L M Ericsson /S Kobenhovn F, Finsensvej, tel: Fa, tgm: ericsson Telefon Fabrtk utomatic /S Kobenhavn K, maliegade, tel: C, tgm: automatic Dansk Signal Industri /S Kobenhavn F, Finsensvej, tel: Fa, tgm: signaler Finland O/Y L M Ericsson /B Helsinki, Fabianinkatu, tel:, tgm: ericssons France Society des Telephones Ericsson Cotombes (Seine), Boulevard de la Finlande, tel: CH -00, tgm: ericsson Port's e, Rue de Courcelles, tel: Carnot -0, tgm: eric teliers Vaucanson, S.. Pans XX. B. P..0, tel: menil -0, tgm: atelcanson Great Britain Swedish Ericsson Company Ltd. London, W. C., High Holborn, tel: Holborn 0, tgm: teleric Production Control (Ericsson) Ltd. London, W. C., High Holborn, tel: Holborn 0, tgm: productrot holb Italy Setemer, Soc. per z. Roma, Via G. Paisiello, tel:.,., tgm: setemer SIELTE, Soc. per z. Roma, C. P. 0 ppio. tel: 0, tgm: sielte F.. T. M. E. Soc. per z. Roma, C.P. 0 ppio. tel: 00, tgm : fat me gencies EUROPE Belgium Electricity et M^canique Suedoises Bruxeltes, Rue de Stassart, tel:, tgm: electrosuede Greece»ETEP» S.. Commerciale & Technique /bens, Rue Lycavitfou, tel: 0, tgm: aeter-athinai Iceland Johan Rdnning H/F Reykjavik, P. O. B., tel: 0, tgm: ronning Ireland Communication Systems Ltd. Dublin, Pembroke Road, Ballsbridge, tel: 0 tgm: crossbar Yugoslavia Merkantile Inozemna Zastupstva Zagreb. Pot pretinac, tel:, tgm: merkantile, telex: 0- SI Burma Burma siatic Co. Ltd. (BC), Ericsson Department Rangoon, P.O.B. 00, tel: 0, tgm: ericsson Formosa (Taiwan) Gadelius & Co. Ltd. Taipei C, P. O. B., tel: 0, tgm: gadeliusco Netherlands Ericsson Telefoon-Maatschappij, N.V. Ri;en (N.Br.), tel: 0-, tgm: erictel den Haag Scheveningen, 0, Palacestraat, tel: 00, tgm: erictel-haag Norway /S Elektrisk Bureau Osio NV, P.B. 0, tel: Centralbord 0, tgm: elektriken /S Industrikontroll Oslo, Teatergaten,tel: Centralbord 0, tgm: indtroll /S Norsk Kabelfabrik Drammen, P. B. 0, tel:, tgm: kabel /S Norsk Signalindustri Oslo, P. B. Mj, tel: Centralbord, tgm: signalindustri Portugal Sociedade Ericsson de Portugal, Lda. Lisboa,, Rua Filipe Folque, tel:, tgm: ericsson Spain Cia Espanola Ericsson, S. - Madrid, Conde de Xiquena, tel: 0, tgm: ericsson Sweden Telefonaktiebolaget L M Ericsson Stockholm, tel: 00 00, tgm: telefonbolaget B lpha Sundbyberg, tel:00, tgm: aktiealpha-stockholm B Ermex Solna, tel: 000, tgm: elock-stockholm B Ermi, Karlskrona, tel: 00, tgm: ermibolag-karlskrona B Rifa Bromma, tel: 0, tgm: elrifa-stockholm B Svenska Elektronrbr Stockholm 0, tel: 0 0, tgm: electronics L M Ericssons Driftkontrollaktiebolag Soma, tel:, tgm: powers-stockholm Hong Kong The Swedish Trading Co. Ltd. Hongkong, P. O. B. 0, tel: -, tgm: swedetrade Iran Irano Swedish Company B. Teheran, Khiabane Sevom Esfand, tel:, tgm: iranoswede Iraq Koopman & Co. (Iraq) W.L.L. Baghdad, P. O. B., tel:, tgm: koopiraq Japan Gadelius & Co. Ltd. Tokyo C, P. O. B., tel: 0-, tgm: goticus Kuwait Latiff Supplies Ltd. Kuwait, P.O.B., tgm: latisup Lebanon Swedish Levant Trading (Elie B. Helou) Beyrouth, P. O. B., tel:, tgm: skefko Pakistan Vulcan Industries Ltd. Karachi City, P. O. B.. tel: 0. tgm: vulcan Philippines Koppel (Philippines) Inc. Manila P. R., P. O. B., tel: --, tgm: koppel Saudi rabia Ceylon Mohamed Fazil bdulla rab Vulcan Trading Co. (Private) Ltd. Jeddah, P. O. B., tel: 0, tgm : Colombo,. York Street, lei: arab -, tgm: vultra Singapore and Malaya China The Swedish Trading Co. Ltd. The Ekman Foreign gencies Singapore, Chartered Bank Ltd. Shanghai, P. O. B., tel: Chambers, Battery Road, tel: -, tgm: ekmans, tgm: swedetrade Syria Georgiades, Moussa & Cie Damas, Rue Ghassan, Harika, tel: -0-, tgm: georgiades L M Ericssons Signalaktiebolag Stockholm Sv, tel: 0 00, tgm: signalbolaget L M Ericssons Svenska Forsaljningsaktiebolag Stockholm, Box, tel: 00, tgm; ellem Mexikanska Telefonaktiebolaget Ericsson Stockholm, tel: 0000, tgm: mexikan Sieverts Kabelverk B Sundbyberg, tel: 0, tgm: sievertsfabrik-stockholm Svenska Radioaktiebolaget Stockholm, lstromergatan, tel: 0, tgm: svenskradio B Ostmarks Lasfabrik Eski/stuna, Munktellsgatan, tel: Switzerland Ericsson Telephone Sales Corp. B, Stockholm, Zweigniederlassung Zurich Zurich, Postfach Zurich, tel:, tgm: telericsson West Germany Ericsson Verkaufsgesellschaft m. b. H. DUsseldorf, Postfach, tel:, tgm: erictel SI India Ericsson Telephone Sales Corporation B New Delhi, P.O.B.. reg.mail: / saf li Road (Delhi Estate Building), tel:, tgm: inderic Bombay, Manu Mansion,, Old Custom House, tel: 0, tgm: inderic Calcutta, P. O. B., tel: -, tgm: inderic Indonesia Ericsson Telephone Sales Corporation B Bandung, Djalan Dago, tel:, tgm: javeric Djakarta, Djalan Gunung Sahari, tel: Kota, tgm: javeric Lebanon Telefonaktiebolaget L M Ericsson, Technical Office Beyrouth, Rue du Parlement, Immeuble Bisharat, tel:, tgm: ellem Thailand Ericsson Telephone Sales Corporation B, Bangkok, P. O. B., tel:, tgm : ericsson Thailand Ericsson gency Office, Telephone Organization of Thailand Bangkok, Ploenchitr Road, tel:, tgm: telthai British East frica Transcandia Ltd. Nairobi, Kenya, P. O. B., tel:, tgm: transcanda Congo (Fed. Rep.) Societe nonyme Internationale de Telegraphie sans Fil (SIT) Bruxe//es (Belgique),, Boulevard du Regent, tel: 00, tgm: wireless (For maritim radio and carrier) Ethiopia Swedish Ethiopian Company ddis baba, P. O. B., tel:, tgm: etiocomp Ghana The Standard Electric Company ccrd, P.O.B.. tel:, tgm: standard Liberia Swedish gencies Liberia Co. Monrovia, P.O.B. 0, tel:, tgm: salco Libya The Gulf Trading Co. Tripoli, P.O.B., tel:, tgm: guitraco Mauritius Mauritius Trading Co. Ltd. Port Louis, P.O.B. 0, tgm:agentou Morocco Elmar S.. SEYRE Tangier, Francisco Vitoria,, tel: -0, tgm: elmar Turkey Ericsson Turk Ticaret Ltd. $irketi nkara, dii Han, Zafer Meydan't, Yei ellem Istanbul, Istanbul Burosu, Liman Han, Kat, No., Bahcekapi, tel: 0, tgm: ellemist FRIC Egypt (UR) Telefonaktiebolaget LM Ericsson, Egypt Branch Cairo, P. O. B., tel:, 0, tgm: elleme Rhodesia LM EricssonTelephoneCo. (Pty.) Ltd. (Branch Office of LM Ericsson Telephone Co. Pty. Ltd. in Johannesburg) Salisbury, Sou/hern Rhodesia, P.O.B., tel: 0 0, tgm: ericsson Republic of South frica L M Ericsson Telephone Co. Pty. Ltd. Johannesburg, Transvaal, P. O. B. 0, tel: -, tgm: ericofon Tunisia Telefonaktiebolaget LM Ericsson, Technical Office Tunis, Boite Postale 0, tel: 00, tgm: ericsson - MERIC rgentine Cia Sudamericana de Telefonos L M Ericsson S.. Buenos ires, Casilla de correo 0, tel: 0, tgm: ericsson Corp. Sudamericana de Telefonos y Telgrafos S.. Buenos ires, Casilla de correo 0, tel: 0, tgm: cartefe Cia rgentina de Telefonos S.. Buenos ires, Peru, tel: 0 0, tgm: catel Cia Entrerriana de TeleTonos S.. Buenos ires, Peru, tel: 0 0, tgm: catel Industrias Elextricas de Quilmes S.. Quilmes FCNGR, de Octubre 00, tel: 0-, tgm: indelqui-buenosaires Brazil Ericsson do Brasil Comercio e Industria S.. Rio de Janeiro, C. P. 0, tel: -00, tgm: ericsson Sao Paulo, C. P., tel: -, tgm: ericsson Canada LM Ericsson Ltd. Montreal, P.Q., 00 Laurentian Boulevard, City of St. Laurent, tel: 0, tgm: caneric Toronto, Ont., P. O. B., tel: BE -0 Mozambique J. Martins Marques Lourenco Morgues, P. O. B., tel:, tgm: tinsmarques Nigeria I.P.T.C. (West frica) Ltd. Lagos, P.O.B. 0, tel:, tgm: consult Vietnam Vo Tuyen Dien-Thoai Viet-Nam, Saigon, Dai-lo Thong-Nhut, tel: 00, tgm: telerad Sudan. FRIC TECOM Technical Consulting and Machinery Co. Ltd. Khartoum, P.O.B., tel:, ext., tgm: sutecoma MERIC Bolivia Johansson & Cia. S.. La Paz, Casilla, tel: 00. tgm: Johansson Costa Rica Tropical Commission Co. Ltd. San Jose, partado, tel:, tgm: troco Cuba Mc voy y Cia Habana, partado, tel: -, tgm: macavoy Curacao N. W. I. S. E. L. Maduro&Sons, Inc. Curacao, P. O. B., tel: 00, tgm: madurosons-willemstad Dominican Republic Garcia & Gautier, C. por. Santo Domingo, partado, tel:, tgm: gartier Guatemala Nils Pira Ciudad de Guatemala, partado, tel:, tgm: nilspira-guatemala Hondur- Quincho ga/pa, ^ tgm: qui.., tthi, tgm: ericsson-santiagodechile Colombia Cfa Ericsson Ltda. Bogotd, partado ereo 0, tel: --00, tgm: ericsson Ecuador Tel fonos Ericsson C.. Quito, Casilla Postal, tel: 00, tgm: ericsson Mexico TeleTonos Ericsson S.. Mexico D.F., partado, tel: 0, tgm: coeric Industrie de Telecomunicacion S.. de C.V. Mexico. D.F., Londres No., tel: 00, torn: industel Peru Cia Ericsson S.. Lima, partado, tel:, tgm: ericsson Soc. Telefnica del Peru, S.. requipa, Casilla de Correo, tgm: telefonica El Salvador Telefonaktiebolaget LM Ericsson, Technical Office, San Salvador, partado Postal, tel:, Igm: ericsson Uruguay Cia Ericsson S.. Montevideo, Casilla de Correo, tel: --, tgm: ericsson US The Ericsson Corporation New York, N. Y., 00 Park venue, tel: Murray Hill -00, tgm: erictel North Electric Co. Galion, Ohio, P. O. B., tel: Howard -0, tgm: northphone-galionohio Venezuela Cia nnima Ericsson Caracas, partado, tel:, tgm: ericsson Telefonos Ericsson C.. Caracas, partado, tel:, tgm: tevela USTRLI & OCENI j ustralia L M Ericsson Telephone Co. Pty. Ltd. Melbourne C (Victoria), 0 Collins Street, tel:, tgm: ericmel L M Ericsson Trimax Pty. Ltd. j Coburg N (Victoria), P.O.B., ' tel: 0, tgm: trimax Jamaica and Brit. Honduras Morris E. Parkin Kingston, P.O.B., tel; 0, tgm; morrispark Nicaragua Edmundo Tefel Managua, D.N., partado Postal, tel: 0, tgm: edfelco Panama Productos Mundiales, S.. Panama, R. P., P. O. B., tel: -0, tgm: mundi Paraguay S.. Comercial e Industrial H. Petersen suncion, Casilla, tel:, tgm: pargtrade Puerto Rico Splendid Inc. San Juan, P. O. B., tel: -0, tgm: splendid El Salvador Dada-Dada & Co. San Salvador, partado, tel: 0, tgm: dada Surinam C. Kersten & Co. N. V. Paramaribo, P. O. B. 0, tel:, tgm: kersten Trinidad, W. I. Leon J ch Ltd. Por/-of-Spam, 00 Frederick Street, tel:, tgm: achegram 'J I US Clark Walter Corporation Nei ark, N. J., Broad Stree tel: Mitchell -, tgm: wire walter-newarknj. (For intercom State Labs. Inc. New York, N. Y., Park venue South, tel: Oregon -00, tgm: statelabs (For electron tubes). USTRLI & OCENI.

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41 ERICSSON REVIEW Vol. XXXIX No. RESPONSIBLE PUBLISHER: HUGO LINDBERG EDITOR: SIGVRD EKLUND, DHS EDITOR'S OFFICE: STOCKHOLM SUBSCRIPTIONS: ONE YER $.0; ONE COPY $ 0.0 CONTENTS Transistorized Group Translating Equipment for Carrier Terminals page Planning of Multi-exchange Networks with aid of a Computer Portable 0-line Switchboard L M Ericsson News from ll Quarters of the World On cover: Rack-mounted telephc ane relay sets, viewed from the wiring side. COPYRIGHT TELEFONKTIEBOLGET LM ERICSSON PRINTED IN SWEDEN, ESSELTE B. STOCKHOLM

42 Transistorized Group Translating Equipment for Carrier Terminals P- HLLBERG & H SCHILLING, TELEFONKTI EBO LGET L M ERICSSON, STOCKHOLM UDC.. LME This article is associated with the description of the channel translating equipment for carrier terminals given in Ericsson Review No.,. In addition to the group translating equipment the description covers the pilotcontrolled level regulation of the basic group and also an equipment for signalling blocking when there is a break in the transmission path. The line frequency allocations of multi-circuit carrier systems for 0 to,00 circuits are founded on the use of supergroups whose basic frequency range is - kc/s; by means of further modulations these are translated to form the line frequency band or can be through connected at basic supergroup frequencies between different systems. Jn accordance with the recommendations of the CCITT the basic supergroup is formed from five groups; the basic group B lies in the frequency band 0-0 kc/s. These groups are inverted in the process of modulation, whereby all the channels come to have an erect attitude. lternatively, the group lying at the top end of the basic supergroup band can have inverted channels: this is used in certain 0-circuit systems. I. Modulation Plan The main duty of the group translating equipment is to modulate five basic groups to form a basic supergroup in accordance with the modulation plan, fig.. n inversion is obtained due to extraction of the lower sideband after modulation and channels having an erect attitude in the basic supergroup are obtained from channels with inverted attitude in the basic group. To enable dministrations who wish to do so to have the possibility of keeping the channels inverted in the basic group transposed to the frequency band 0- kc/s, there is a different type of modulator which uses a carrier frequency of kc/s. The levels at the terminal strips can be adjusted between certain limits as the outgoing supergroups and incoming groups pass through coaxial plugs with built-in pads. In addition it is possible to have or 0 ohms balanced instead of the nominal impedance of ohms balanced on the basic group side. The. kc/s supergroup reference pilot is added to the basic supergroup immediately after its formation. It is also possible to introduce the.0 kc/s group reference pilot in the basic groups if this has not been done previously. Fig. Modulation plans for formation of alternative supergroups x e 00kc/s

43 The level of the basic groups on the receiving side can be regulated manually or automatically, the basic group level in this case being controlled by the group reference pilot level. larm can be sent out if tolerable deviations from nominal level are exceeded. In the case of carrier systems using continuous signalling of the tone idle type, an interruption in the line causes a loss of tone and produces the same effect as a call on every free circuit. To prevent a mass call to the exchange which can have deleterious consequences, the signalling receivers in the channel translating equipment are blocked by means of a rapid acting pilot receiver responding to. kc/s. Special attention has been devoted to maintenance facilities in the development of this equipment. The inputs and outputs on the group and supergroup sides are provided with protected test points where measurements can be made irrespective of the impedance of the equipment connected and the transmission circuit is not affected by a short circuit in the test point. When fault-finding, different parts of the system can be isolated by means of U-links. Fault localization is made very much easier by using the faultfinding test points provided on the units. Each unit meets very stringent performance limits so that it can be replaced by a similar unit without involving any subsequent adjustments. The group translating equipment also fulfils the requirements for transmission of carrier programs (sound broadcasting). The group translating equipment is built in accordance with the same modern design principles used in the channel translating equipment. New components and materials such as transistors and ferrites mounted on cards with etched wiring and contained in protecting cases give compact, stable and well-screened units. detailed description of L M Ericsson's new method of construction and components is given in Ericsson Review no., 0 and Fig. x no.,, " New Method of Construction for Transmission Equipment". Mechanical construction of group The appearance of the group translating equipment mounted in a bay is seen translating equipment in fig..

44 0-0 ^rv -TV s\- ^rv Bfiwi«Niai- ^IV i»m*ki% mk M ~ _L Utl*l*Ml feeeh «' ts ( -^ F=E} as /-* ai; {B^l - -TV p=a- LT«I I M drlh T <S -r> (<} -Ti [«} Win I M H&- TOIT- 0 TT J/- ^O^- F=m- Qfi W E > Fig. Block schematic of group translating equipment II. Modulation Equipment The principle of the group translating equipment wil schematic, fig.. be seen in the block Sending direction The basic group at a nominal level of - dbr enters the translating equipment via a U-link. For input levels in the range - dbr to - dbr, the levels at different points in the sending equipment are correspondingly lower. The nominal impedance on the basic group side is ohms unbalanced. matching transformer is introduced before the U-link if it is desired to obtain an impedance of ohms or 0 ohms balanced. test point for measuring purposes is provided at the input to the group modulator to permit checking of the level of the basic group. The basic group frequency band is translated in the group modulator to its position in the basic supergroup using one of the five group carriers. If the group lying in the frequency band 0- kc/s is required to be inverted, a carrier of kc/s is used instead of kc/s and the upper sideband is selected. This is obtained by plugging into the bay a different modulator unit which, since its carrier input uses different contacts, automatically receives the correct carrier frequency.

45 T W" iqnq i J - r -i'vv-o Fig. Circuit diagram of modulator and filter X The modulator is of double balanced type of a special design which has been patented by L M Ericsson, see fig.. With this circuit the conducting diodes do not reduce the carrier voltage to the non-conducting diodes thus giving the same sideband power with lower carrier power. n even greater advantage is that good total harmonic ratios are obtained. The modulators therefore give a negligible contribution to intermodulation noise. In order to obtain optimum results using as few elements as possible, the filters have been calculated using a modern electronic computer. very low attenuation distortion has been obtained by compensating the filters for dissipation, thus avoiding the need for correcting networks. By compensating for dissipation the filter impedance rapidly becomes high in the stop bands, thus leading to negligible mutual interference. The design is shown in fig., and the attenuation characteristic in the stop bands is shown in fig.. The five group filters belonging to a supergroup are connected together alternately on either side of a symmetrical differential primary winding of a hybrid transformer. This is also provided with a differential secondary winding which is unsymmetrical so as to permit injection of the. kc/s supergroup reference pilot. The injection is independent of the impedance of the filters connected together. The level of this pilot lies 0 db below the level of the channel test tone. pad can be connected into the pilot path so as to retain this ratio even when a lower speech path level is used in the sending direction. Fig. Group modulator and filter The whole supergroup band is amplified in a supergroup amplifier using two transistors. The secondary side of the output transformer is formed of differential windings where the maintenance test point is branched off. It is therefore possible to carry out correct measurement even if the equipment connected to the test point is not correctly matched. n incorrect manipulation in the test point does not disturb the transmission in the main circuit. W / Fig. 00 kc/s x M ttenuation graph for group modulator filter Some Telephone dministrations use a supergroup sending level of - dbr or less. In this case the amplifier need not be used and may be replaced by a dummy unit which is provided with a branching network to feed the maintenance test point. The supergroup passes out from the equipment via a U-link which contains a pad for matching purposes. The nominal supergroup sending level is - dbr and the impedance is ohms unbalanced. Receiving direction The incoming supergroup at a level of - 0 dbr passes via a U-link to the receiving equipment. The U-link is provided with a built-in pad if the incoming level is higher. maintenance test point which is protected from interference and an outlet for the. kc/s reference pilot frequency to a signalling blocking equipment described below in section IV are obtained from a hybrid transformer provided with differential windings on the primary and secondary sides.

46 The supergroup frequency band passes through a hybrid transformer where it is split up and distributed to the group filters. The demodulator and filter unit are of the same type as on the sending side which is an advantage from the spares point of view. The demodulator is followed by a low-pass filter which ensures that carrier leak and the unwanted sideband are suppressed to such a low level that they do not load the subsequent amplifiers or make measurements difficult. The final suppression occurs in the channel translating equipment or in a through connexion filter. The supergroup reference pilot must be stopped so as not to cause interference when through connecting groups or when receiving out-band signals. The pilot is stopped after demodulation, its frequency then being 0.0 kc/s. The pilot stop filter consists of three sections each of which is a bridge circuit with a crystal in the shunt arm. The filter attenuates the pilot by at least 0 db. Each of the basic groups is amplified by two identical amplifiers connected on either side of a level regulating network. short-circuit-proof maintenance test point for determination of the level at the input to the level regulating network is branched off via a differential circuit from the output of the first amplifier. The level regulating network consists of a d.c. controlled attenuator or an adjustable pad which can be set by a rotary switch. The two types permit compensation of a deviation of level of ± db from nominal. The first type of network consists of a bridged T-network with indirectly heated thermistors in the bridge and shunt arms. With this arrangement the attenuation is not affected by changes in ambient temperature or in the supply voltage. If the latter disappears completely, the attenuation reverts to the nominal value. The advantage of a thermistor attenuation network is that a change of the level setting occurs entirely without interference or sudden changes of level in the transmission path. The direct current control is obtained from a manually adjustable potentiometer or from one which is automatically adjusted. In the latter case, this is controlled from a centralized pilot receiver, described in section III below. This pilot receiver, which is also used for sending out an automatic alarm, is connected in turn to each basic group. The level at which the basic group leaves the second amplifier can be checked at a short-circuit proof maintenance test point. The differential winding which branches off this test point from the amplifier also feeds the centralized pilot receiver. The basic group leaves the equipment via a U-link which is not normally provided with a pad. s in the case of the sending direction, the nominal impedance of or 0 ohms balanced can be obtained by using a matching transformer, instead of the usual impedance of ohms. III. utomatic Regulating and Supervisory Equipment By means of a centralized pilot receiver the level of the basic groups can be automatically regulated and supervised or alternatively only supervised. When regulating, the pilot receiver affects a memory element which in turn controls the attenuating network in the transmission path. When supervising, the central unit sends out an alarm if there are large deviations in the level of any group, and at the same time the particular group at fault is indicated by an individual lamp. The centralized pilot receiver may be used for up to 0 groups.

47 <^^-ra *- larm Fig. x Block schematic of automatic group regulation and supervision Fig. shows a very simplified block schematic and a more detailed schematic is shown in fig.. The connexion of the groups in turn to the centralized pilot receiver is carried out by a chain of relays which steps automatically. Each group is connected for about 0 seconds. When all incoming groups have been checked and before the chain of relays starts a new interrogation cycle, the group reference pilot generator of the station is connected. larm is given if the pilot level there deviates by more than 0. db from the nominal value. The station group reference pilot and the centralized pilot receiver are thus checked in this way. Fig. x Different types of level supervision units Lek, automatic level adjuster with stepping motor; centre, manual setter with level supervision relay; right, manual level setter only

48 The group whose turn it is to be checked is connected from the test output at the output of the second amplifier in the transmission path receiving direction, to the input of the pilot equipment via a reed relay. The signal is amplified in a normal type group amplifier and the.0 kc/s pilot frequency is selected in a crystal filter of ladder type using three crystals in the series arms. The attenuation of interfering speech and out-band signalling frequencies is shown in fig. 0. The pure pilot frequency is amplified in two amplifiers connected in cascade and is then passed to the electronic level sensing device. The pilot level can be measured at the input to the device and read off on a built-in meter. The level sensing device consists of several electronic trigger circuits, each of which is set to operate at a different voltage. The voltages are chosen so that a level deviation of more than + 0. or -0. db from nominal operates one of the regulation trigger circuits. greater deviation which may be set to ± db, ± db or ± db by means of soldered straps causes one of the alarm trigger circuits to operate a reed relay whose make contact closes a common alarm circuit. When there is a level deviation requiring regulation, the controlling memory device is operated by a control relay. The memory device consists of a potentiometer driven by a stepping motor whose design is patented by L M Ericsson: this rotates through a small defined angle in one or the opposite direction when an electrical impulse is applied and remains in this position until the next impulse arrives. The stepping motor does not contain any mechanical contacts; all coupling occurs magnetically thus giving maximum reliability. The potentiometer divides the voltage between the two thermistors in the attenuating network in the transmission path, as mentioned earlier. This part of the equipment is not supplied if only automatic supervision is required. When there is a level deviation sufficient to cause an alarm, the make contact mentioned above not only gives central alarm but also lights a lamp associated with the faulty basic group. This lamp remains lit by means of hold contacts until a reset key has been operated. In addition, the regulation of this basic group level is blocked, thus avoiding incorrect level adjustment. If, due to a slow change of level, the potentiometer wiper reaches either of its end positions, the lamp will likewise light. The basic group reference pilot levels can be read off on a built-in meter, using a rotary switch to select the desired basic group. When the measurement button is depressed, the automatic stepping relay chain is disconnected while the selected basic group and the meter are connected into circuit. The equipment described has a number of advantages over the method using individual pilot receivers. bove all, the centralized pilot receiver saves both space and expense. s the regulating element is provided with a memory, the attenuation of the network connected in the transmission path is unchanged if for any reason there is an interruption in pilot transmission so that when speech transmission is restored after an interruption, there is no reduction of stability margins. IV. Signalling Blocking Equipment When a carrier system is provided with low level out-band signalling, a signalling system of "tone idle" type is often used. This means that the signalling tone is sent as long as the channel is free and that the signalling tone is absent when a call is in progress. The tone remains absent for the whole duration of the call and its return means the end of the call.

49 Channel translating equipment I. - Group translating equipment Signal Fig. Block schematic of signalling blocking equipment X The consequence of this is that a break in transmission would result in seizing signal on all free circuits, which could cause overloading of the exchange equipment. To prevent this the signalling receivers in question can be blocked immediately when there is a break in the connexion. This is carried out by a special pilot receiver as soon as the supergroup reference pilot frequency. kc/s is absent. This is thus used as the criterion for an unbroken connexion. The principle of the equipment will be seen in the block schematic, fig.. From the differential transformer at the input of the receiving side of the modulating equipment, some of the supergroup signal is passed via an h.f. U-link to a transistorized amplifier, the standardized supergroup amplifier. fter amplification the pilot frequency. kc/s is extracted by a crystal filter consisting of a bridge filter with two crystals, is amplified again in a similar amplifier and applied to the sensing device. Here the pilot voltage is rectified and compared with a standard voltage. The difference voltage is sufficient to hold an electronic trigger operated with sufficient margin. This trigger operates a mercury relay of the type used in the signalling receivers. When the pilot voltage is too low or disappears completely, the relay releases and relay voltage is connected across its break contact via a v.f. U-link to the signalling receivers of the channel translating equipment. s long as no call is in progress, an extra winding in its relay is affected so that this is held in the operated position despite the disappearance of the signal, and no seizure signal is sent out. The circuit through the relay is closed through its own change-over contact to signalling earth. If a call is in progress, the signalling receiver relay is not operated and the hold circuit for the blocking voltage is open. t the same time as the relay voltage is connected to the channel translating equipment, it is also applied to a lamp and a thermal relay. This ensures that the above-mentioned signalling earth is disconnected via an auxiliary relay after about 0 sees. Release signal is then given in all circuits and all calls are cleared. larm is also sent out at the same time. The v.f. U-link can be removed for maintenance purposes. The whole of the equipment connected to this except for the lamp is thereby disconnected. t the same time the sensitivity of the receiver is reduced, thereby checking that it does not operate too close to the limit. When the U-link is plugged into the jack placed adjacent to it, the sensitivity is appreciably reduced and the receiver relay must release for correct function. This is observed on the lamp.

50 V. Technical Data FREQUENCY RNGE Nominal frequency range of basic group 0-0 kc/s Nominal frequency range of basic supergroup.. - kc/s The group in the frequency range 0- kc/s can be inverted by using an alternative modulator unit. NOMINL LEVELS Sending direction On basic group side - dbr On basic supergroup side - dbr Receiving direction On basic supergroup side 0 dbr On basic group side - dbr NOMINL IMPEDNCES On basic group side, sending and receiving directions On basic supergroup side, sending and receiving directions VRITION OF EQUIVLENT ttenuation/frequency distortion in the range 0-0 kc/s band relative to.0 kc/s when measured with groups looped at basic supergroup frequencies does not exceed CRRIER LEKS Level of any group carrier, measured selectively in the basic supergroup sending direction with ohms termination does not exceed INTELLIGIBLE CROSSTLK The near-end and far-end crosstalk ratio for all combinations of basic supergroups is greater than UNINTELLIGIBLE CROSSTLK Inverted crosstalk measured at the distribution frame is greater than supergroup NOISE Basic noise (without loading in speech or signalling channel) measured psophometrically at a point of zero relative level is less than Noise in a loaded system Total mean noise per channel measured psophometrically at a point of zero relative level with all other channels loaded with white noise at a level of -. dbmo per channel is less than POWER SUPPLY Transistor voltage Relay voltage Power consumption for one supergroup (depending on the number of pilot receivers connected) ohms unbalanced, alternatively, or 0 ohms balanced ohms unbalanced ± 0. db - dbmo 0 db db 0 pw pw - V - V 0- W Fig. Group translating bay ZDG VI. Use of the Supergroup in different L M Ericsson Carrier Systems In this section, some examples will be given of group translating bays used in different carrier systems, i.e. the group translating bay ZDG and the combined group and supergroup translating bay ZDG.

51 Group Translating Bay The group translating bay is used in large stations where there are many supergroups. This is the case when a coaxial cable carrier system is to be built up and also when several 0-circuit or 0-circuit systems are included. The bay contains equipment for modulation of 0 basic groups to basic supergroups. The levels of the incoming groups are adjusted to that of the equipment by means of plug-in pads. The impedance on the basic group side which is nominally ohms can, alternatively, be or 0 ohms. By making a simple exchange of a plug-in unit, the upper group in the CCITT basic supergroup can be inverted. Regulation of the received groups can either be made automatically using a centralized pilot receiver or manually using indirect control. utomatic supervision can also be provided with either of these two alternatives. Finally, direct level regulation using a switch can be provided. ll these alternatives can be combined with each other as required and are simply obtained using plug-in units. To prevent mass calling of the exchange if there is a break in transmission when using a signalling system of the type "tone idle", a special pilot receiver can be connected to each supergroup which blocks the signalling receivers in the channel translating equipment. Fig. shows the appearance of the bay and its mechanical construction. Immediately below the terminal strips at the top of the bay is seen the - Volt power supply unit for operation from 0, or 0 volts a.c. at a frequency of - c/s. lternatively, a - V d.c. battery can be connected to the bay. The output from the filter panel placed at the right of the power supply unit is used as transistor voltage. t the left is an alarm unit which is common to all alarms sent from pilot receivers, fuses, etc. in the bay. Below the power units are seen the pilot receivers for signalling blocking. In the centre of the bay are seen the meter and switch with the associated regulating pilot receivers placed above and to the right and left of the meter and switch. The controlling elements for level regulation are placed below the meter. The remaining space in the bay is occupied by the six sets of group translating equipment. Fig. Group and supergroup translating bay ZDG Group and Supergroup Translating Bays for 0-circuit and 0-circuit Carrier Systems for Radio Links One bay contains equipment for group and supergroup translating equipment for four supergroups which can alternatively be used for four 0-circuit carrier systems for radio links or two 0-circuit carrier systems for radio links. The frequency ranges for the 0-circuit system are - kc/s or 0-00 kc/s and - kc/'s or 0- kc/s for a 0-circuit system. The group translating equipment is identical with the equipment described previously.

52 Planning of Multi-exchange Networks with aid of a Computer YRPP, TELEFONKTIEBOLGET LM ERICSSON, S T O C K H O L M UDC.. LME 0 The planning of multi-exchange networks may involve extremely extensive numerical calculations. This applies especially to problems of determining the number of exchanges, their locations and boundaries, the traffic distribution between exchanges after modification of the network structure, and finally to the allocation of junctions between direct and tandem routes. To simplify this work, L M Ericsson has developed methods which permit programming of the most laborious operations for an electronic computer. The questions of exchange locations and boundaries, and the traffic between the exchanges, are dealt with briefly below. The structure of junction circuits will be considered later. Detailed discussions of these problems will be published shortly in Ericsson Technics. I. Locations and Boundaries of Exchanges in Multi-exchange reas The outside plant usually represents more than 0 per cent of the total cost of a telephone system. ny saving that can be made on outside plant is therefore an important factor in the economy of the system as a whole. L M Ericsson's automatic telephone systems are characterized by very high flexibility and are adaptable to any desired network configuration. Networks can therefore be planned without any limiting conditions imposed by the circuitry. In the planning of a multi-exchange network it is essential to make a correct estimate of the number of exchanges required and of their locations and boundaries. These are the basic data required for the detailed planning of subscribers' and junction cables and tandem stages. But to determine the number of exchanges, and their locations and boundaries, so as to arrive at as small as possible an overall cost, often requires such extensive numerical calculations that one does not consider one can perform them with the necessary accuracy. The reason may be either shortage of staff or quite simply that one does not consider it worth the trouble and cost. L M Ericsson has therefore made a study of this question with the aim of deriving methods for planning the locations of exchanges and their area boundaries which would permit the most laborious calculations to be programmed for a computer. This study, which has now been completed, opens up entirely new possibilities of economic planning of multi-exchange networks. The calculations can be made quickly, which brings great savings in time and money. One can also calculate on different assumptions concerning future developments both as regards subscriber growth, geographical distribution and the anticipated technical development questions which can hardly be dealt with satisfactorily without a computer. The underlying principles are set out in detail in a paper in Ericsson Technics No.,, entitled "Planning of Exchange Locations and Boundaries in Multi-Exchange Networks". The present article will contain a brief survey of the calculation procedure and of the input and output data.

53 The planning of a multi-exchange network is based on a map divided into equal squares in which the numbers of subscribers are indicated. This subscriber inventory, which should apply to a point of time 0-0 years ahead, is made up from quarterly counts, building plans and statistical data describing the growth of population and telephone density. One starts by estimating the number of exchanges required. The optimal result is obtained by comparing the total costs on the assumption of different numbers of exchanges. In determining the locations and boundaries of the exchanges, one starts by assuming that the volumes of traffic initiated and received by all subscribers within the area are equal and that the junction network is mesh-shaped. To allow some consideration for the differences in community of interest between the exchange areas, an upper and a lower limit for this factor should be estimated. Cable types that is, conductor diameters and loading in the subscribers' and junction networks are estimated by fixing the exchange locations and area boundaries on trial. distinction is made between exchanges whose locations are known, i.e. existing exchanges which are not to be moved or exchanges the location of which is fixed by other factors, and exchanges whose locations must be determined. The input data for the computer before the calculation is started are: The subscribers' inventory (one or more forecasts). In this inventory the positions of squares are indicated by row and column. Thus a it indicates that a subscribers are located in the square defined by row i and column /. Fixed locations of exchanges. (The exchange locations are determined by indication of row and column.) Locations of exchanges which are to be determined. Upper and lower limits for estimated traffic initiated per subscriber. Formulae indicating relation between volume of traffic and number of junctions. Unit costs for subscriber's and junction cables. The calculations are then started in the computer and proceed roughly as follows: a) The boundaries between the exchange areas are determined from. locations of exchanges fixed on trial (input data). unit costs of subscribers' cables (input data). b) The subscribers' inventory and the number of subscribers for each exchange area are determined from. the subscribers' inventory for the whole area (input data). exchange boundaries determined under a). c) The number of junction circuits between each two exchanges is determined from. subscribers' inventory for each exchange area as under b). traffic initiated per subscriber (input data). relation between volume of traffic and number of junctions (input data). d) New exchange locations are determined from. number of subscribers for each exchange area as under b). number of junctions as under c). unit costs for subscribers" and junction cables (input data).

54 e) New exchange boundaries are determined from. exchange locations determined as under d). number of subscribers within exchange areas under b). relation between increase in number of junctions and increase in volume of traffic (input data). unit costs of subscribers' and junction cables (input data). The process is then iterated from b), using the exchange boundaries under e), until a predetermined value for the change of exchange locations is not exceeded. The computer delivers the following printed data: Exchange locations Exchange boundaries Number of subscribers within each exchange area Mean length of line for each exchange area and the distribution functions showing the number of subscribers beyond different distances from the exchanges. For a large number of exchanges it may be advisable to arrange also for the computer to print a table of the costs of the various subscribers' and junction networks, the total of these costs, and the number of junctions, to facilitate an approximate cost comparison for different numbers of exchanges. ll these data are obtained both for the upper and lower estimated limits of traffic initiated per subscriber, and in this way one generally acquires fully adequate figures for determining the locations and boundaries of the exchanges. survey of the calculating procedure and of the computer input and output data is shown in tabular form below. Survey of calculating procedure X Input data Boundaries of exchange areas a) Inventorics and numbers of subscribers for the exchange areas b) Number of junction circuits c) New exchange^ locations d) r ^ New exchange boundaries e) Output data Subscribers' inventory Exchange locations a) fixed b) estimated Traffic initiated per subscriber b) lower limit Q Formulas a) relation between traffic and num- w ber of junctions b) increase in num- -». L L?? Exchange locations Exchange boundaries Number of subscribers within exchange areas Mean length of line within exchange areas; distance distribution of subscribers from exchanges for traffic increase of erlang Unit costs a) subscribers' b) junction cables "s«i fj [Cost of subscribers' cables. Specification of junction circuits: a) number b) cost]

55 If greater accuracy is required, which may be desirable in areas where there is a considerable difference in the community of interest between different exchanges, one should make a new calculation after charting and calculating the junction circuits on the basis of traffic counts. fter these calculations one can enter the result on the map and make whatever adjustments may be necessitated by housing schemes, geographical factors, transmission conditions, etc. If the deviations are considered too large, a new calculation will have to be made; otherwise the exchange locations and area boundaries will now have been established, and the total cost of subscribers' and junction cables and exchange equipments can be estimated. The procedure is then repeated in its entirety with other assumptions as to the number of exchanges. The most favourable solution is finally selected, after which one can proceed with the detailed planning of subscribers' and junction cables, exchange equipments and tandem stages. II. Inter-Exchange Traffic In a multi-exchange network one is often confronted with the problem of determining the quantities of traffic between and within the different exchange areas after some change has been made in the structure of the network. Such changes arise through the expansion of existing exchanges, the introduction of new exchanges, or the division or merging of two or more exchange areas. The distribution of the traffic between exchanges provides a means of determining the number of switches required in the exchanges, the location of tandem stages, the size of tandem areas, and the numbers of circuits on direct and tandem routes. This traffic distribution must be estimated for a future point of time determined by the anticipated development and the time taken to supply the equipment required. To estimate the traffic distribution in large areas comprising many exchanges involves lengthy calculations; all the more so if, in view of the uncertainty naturally attaching to all forecasts, the calculations are to be made under different assumptions as to the future development. Mechanization of these calculations is therefore very desirable and saves much time and money. The traffic distribution can be determined by different methods depending on the knowledge possessed of the internal traffic distribution between different sub-areas of the multi-exchange network. Let us assume initially that we know this internal traffic distribution. It is then a simple matter to calculate the traffic distribution arising between different exchange areas formed by adding to each area a number of sub-areas. To take a simple example, say that the traffic between four sub-areas,, and is as follows: From To

56 and that two exchange areas I and II are formed as follows: Exchange I II Sub-areas This immediately gives: Traffic direction Within I From I to II Within II From II to I Traffic intensity +++= +++= +++= +++= or summarized in a matrix: This may appear entirely trivial. But with a large number of sub-areas and exchanges the calculation becomes cumbersome, and it is easy to make mistakes. It is therefore of interest that the result can be obtained by setting up the calculation on a routine basis as follows: Sub-area Exchange I Exchange II ~ 0~ and performing the matrix multiplications = (e.g.: J =) and " ~ 0~ L _ (e.g.:-l = ) If, instead, three exchange areas I, II and III are formed as follows: Exchange area Sub-areas I II III the traffic distribution is obtained from the matrix multiplication ~ 0 0 () In addition to the gain in clarity which this method of setting up the problem brings in manual calculations, it allows easy programming for a computer.

57 Often, however, one has no knowledge of the traffic between different sub-areas, and approximate methods must be adopted. Say that the traffic distribution between two exchanges is given by the matrix and that area, which according to the matrix has an initiated traffic of + =, is to be divided between two exchanges I and III. One estimates that the initiated traffic after this division will be for exchange I and for exchange III. No other data of the traffic distribution are available. Provided that the traffic within the new area III, internal and external, is proportional to the internal traffic of the original area, the traffic distribution after the division will be ' " Ts o <n -..-L / \ () This latter estimate, (), usually differs from the preceding estimate (). which was based on the traffic between the various sub-areas being known from the start. lthough the structure of expressions () and () is alike in principle, they represent two entirely different operations. In () a traffic matrix of order x is broken down into a matrix of order X. In (), on the other hand, a matrix of order X is built up from a matrix of order x. n expansion of a traffic matrix in this way can, of course, not be done exactly without a knowledge of the internal traffic distribution. In this simple case, of course, the latter arrangement can be written direct. But when several new exchange areas are to be formed by cutting out portions of one or more existing areas, an arrangement as in () is preferable both for manual and mechanical calculations. s final example we assume that in an area of two exchanges and with the traffic distribution ri L 0 j Total I Total a new source of traffic, III, arises for which we can estimate only the following data: initiated traffic = received traffic = internal traffic =

58 To estimate the traffic distribution on the assumption traffic for exchanges and II is unchanged, one forms that the initiated V = 0. after which the new traffic distribution is determined as follows: = 0 0 Total Total These examples show the most important principles for calculating traffic distributions. The examples can be generalized to embrace multi-exchange networks with arbitrary numbers of exchanges in which new areas are formed by regrouping one or more portions of the existing areas into one or more new areas. The necessity for dividing up a network into several areas may be due to an increase of the traffic in existing areas through the addition of new traffic sources within and/or outside the areas or to the amalgamation of two or more areas under a single exchange. This is described in detail in "Calculation of Traffic Distributions in Multi-exchange Networks" in Ericsson Technics No.,. These calculations can be quickly carried out with a computer, which presents the results printed in tabular form indicating in the customary manner the traffic between and within the exchange areas.

59 Portable 0-line Switchboard T B J O R K M N, TELEFONKTIEBOLGET LM ERICSSON, S T O C K H O L M UDC.. LME L M Ericsson has produced a 0-line portable switchboard which not only has the robustness and full telephonic facilities required for use in the field, but also meets the condition essential in field telephone equipment, that it shall not cause disturbance to radio stations even in its immediate vicinity. The switchboard was designed in close collaboration with the Swedish rmy Ordnance dministration. L M Ericsson's new field switchboard BM 0 is of extremely robust construction. It has facilities for connection of 0 lines and has 0 cord pairs for establishment of 0 connections at one time. The lines from the switchboard can be connected both to magneto telephones and to all kinds of public exchange. Ordinary magneto telephones can be used when the switchboard is to operate solely between magneto extensions and magneto exchange lines. With C.B. exchange lines the magneto telephones must permit of a holding loop being formed through the telephone, and the receiver must be protected against direct current. The switchboard allows direct dialling by extensions, so that the magneto telephones may be fitted with dials. The switchboard is designed to operate on a -volt external source consisting of a storage battery. If there is no -volt battery, or if a temporary interruption takes place in the external power supply, the switchboard will nevertheless function satisfactorily on two -volt dry cell batteries. These batteries are automatically switched into circuit when the external power supply ceases. g 0-line field switchboard BM 0 (left) with transport covers removed (right) ready for transport To ease the work of the operator, the switchboard has a V pole changer X f or generation of ringing current. There is also a hand generator as reserve equipment in the event of failure of the pole changer or absence of a -volt

60 Constructional Features The switchboard is fitted in a robust light alloy case. For transport of (he switchboard two covers should be attached to it, one on the front and one on the rear. Fig. shows the switchboard with and without cover. Slotted into the edges of the covers are rubber weatherstrips which prevent any entry of moisture into the switchboard. The covers are firmly secured to the case by powerful snap type catches. One cover has an inner compartment in which the handset and ten plug-ended cords for conference connections are accommodated during transport (fig. ). The switchboard has two handles. The case and covers are finished in a dark green enamel which is proof against infra-red light. Fig. X 0 Cover with compartment for handset and cords The switchboard chassis, which contains all delicate parts, is mechanically insulated from the case by rubber pads to protect the components against knocks and careless handling. The switchboard with covers weighs kg. Its dimensions are: height 0 mm, width mm, depth mm. The front of the switchboard is shown in fig.. The calling devices and jacks are combined into line units, each serving 0 lines. Four line units are fitted at the upper left-hand side of the switchboard. On the right of the line units is a conference unit which, in addition to conference jacks, contains lamps for illumination of the switchboard. Under the conference and line units are ten switching sets and a position set. These sets are inclined from the vertical for convenience of operation. The rear of the switchboard, on which all wiring connections are made, is shown in fig.. The round sockets marked 0 are for connection of the lines. Every round socket is connected in parallel with its respective rectangular socket to which, when required, various types of supervisory equipment can be connected direct to the lines. The storage battery connects to one of the two jacks marked V, which are in parallel. Standby -volt batteries are accommodated in the rectangular battery boxes MB and SB. Jacks // and OJ are used for concentration of positions when two switchboards are coupled together. n earth conductor must be connected to the terminal at the bottom right, marked with the earth symbol. Fig. X Rear side of switchboard with covers removed Line Units The calling devices consist of drop indicators with 00-ohm d.c. resistance. Being built integral with their respective jacks, the advantage is gained that the indicator is automatically restored when the call is answered by plugging

61 into the jack. In order to be able to connect magneto and C.B. lines to any jacks, a capacitor has been placed in series with the clearing indicator so as to block the direct current from the C.B. exchange. nother capacitor in conjunction with a resistor constitutes the line termination. This is necessary for the avoidance of self-oscillation on amplified lines. ll these components are built into a very stable and compact unit. s seen from fig.. this unit is cabled to two sockets, a circular -pole and a rectangular 0-pole socket, on the rear of the switchboard (fig. ). For adjustment of the indicators the line unit can be pulled out forwards by releasing the two fixing plates. Switching Sets Each switching set consists of two cords with plugs, two cord winders, clearing signal indicator, speak-and-ring key and monitoring key. With ten switching sets ten connections can be set up simultaneously. The switchboard cords coil up on two nylon cord winders. These are a new feature in manual switchboards. Three flat helical springs of stainless steel serve both to wind up the cord and to connect its a, b and c conductors to the switching set. No sliding contacts are employed. The cord cannot be pulled off the winder by mistake, but is nevertheless easy to remove when desired. The clearing indicator has a 000-ohm d.c. resistance. The indicator is in series with a capacitor to permit direct dialling from extensions to exchange lines. The switching set key is of -way type, speaking position up, normal position centre and ringing position down. The clearing indicator is automatically restored when the operator throws the key to speaking position. The switching set is connected to the chassis by plug and jack. It can be removed for adjustment or replacement simply by releasing the two fixing screws. Position Set The position set contains all the necessary common equipment such as dial, speak-and-ring key on answering cord, speak-and-ring key on ringing cord, key for audible calling and clearing signals, and concentration key. The position set also contains the hand generator, ringing indicator and bell.

62 It is connected to the switchboard chassis by plug and jack. It can be removed for adjustment in the same convenient manner as the switching sets, simply by releasing the fixing screws. Conference Unit Conferences can be set up by means of the conference unit (fig. ) and flexible cords (fig. ). Conferences can be established between magneto lines alone or between magneto lines and C.B. exchange lines. Every group of four jacks is connected in parallel. Four lines can be connected together on a vertical row of jacks. If more than four lines are to be in conference simultaneously, two or more rows of jacks can be interconnected by pressing one or both keys in accordance with the engravings on the front panel. The right-hand row, marked CB, is for connection of C.B. exchange lines to a conference. Four jacks and a lamp with red lens are placed under the sign WIT JCKS. This is to remind the operator that a call is waiting for an engaged Fig. X extension. The operator plugs the waiting subscriber's ringing cord into one of Conference unit the jacks, whereupon a lamp lights as a reminder of the waiting call. t the top of the conference unit are two W lamps for illuminating the front panel. The lamps function only off a -volt battery. They have built-in switches which light the lamps when the lamp covers are pulled outwards. The covers can be rotated to direct the light in the desired direction. One lamp should preferably shine on the jack field and the other on the cord pairs. Connection of Lines The line connections are shown in fig.. Every group of 0 lines is run to a terminal box from which distribution cables proceed to the individual extensions and to the public exchanges. The distribution point may be located at a varying distance from the switchboard, depending on the number and length of the line cables between the switchboard and terminal box.

63 Terminal Box The terminal box, BM, has ten pairs of screw terminals for the field telephone lines and an earth terminal for an earth conductor. round -pole socket of the same type as that on the line unit is fitted at one end of the box (fig. ). Overvoltage protectors for the lines are placed in the terminal box, which is watertight. The cover is made of glass fibre reinforced plastic, and the base of a light alloy. The base has three holes for suspension of the terminal box on a tree, wall or other suitable mounting. When no cable is connected to the box, the socket is protected by a cover secured to the box with a chain. Fig. Terminal box BM Line Cable The line cable, type RPM 0 (fig. It)), consists of polythene-insulated conductors stranded around an insulated steel wire. The plastic cover around the conductors is reinforced with steel wire braid. On the outside is a layer of watertight PVC. The cable withstands both high and low temperatures. The line cables are supplied in lengths of, 0 or 00 metres. They have a - pole connector at each end. Battery Cable Every switchboard is supplied with a -metre battery cable with identical plugs at both ends (fig. ). These cables are used for connecting a -volt battery to the switchboard and for interconnecting two boards when operating as an 0-line switchboard. Fig. 0 Line cable type RPM 0 The Multipole Connector The -pole connectors with bayonet grip (fig. ) on the field switchboards were originally designed as coupling device for the line cable. They are made for use out-of-doors under severe conditions. They function satisfactorily at a relative humidity of around 00 per cent within a temperature range of -\- : to 0 C. They are concentrically shaped and are made both for cable grip and panel mounting. The coupling component is identical in both cases, being of threeprong bayonet type. The prongs are placed asymmetrically to ensure correct coupling in only one position. The coupling component is made in one piece on the fore end of a steel casing which supports and encloses the terminal insert. The latter contains individually sprung pin terminals, the spherical surfaces of which are automatically cleaned when two connectors are coupled together. The pins are constructed for soldered termination and are plated with gold over nickel. For panel mounting the connector is fitted with a rubber gasket and lock nut. For cable mounting it is fitted with a rubber cable guard and a metal casing. The casing is attached to the connector by a lock nut and has in its centre a strain-relieving device so designed that all tensile strains are taken up by the centre steel wire and the metal braiding. Both types of connector can be fitted with a cap for protection of the terminals against wet and mechanical damage. Fig. Connector type H0 for panel mounting ' 0-line Field Switchboard If 0 lines should prove insufficient, an 0-line switchboard can be made up by combining two 0-line boards, placed side by side as shown in fig.. ll 0 cord pairs can be used between any jacks in either switchboard.

64 Fig. 0-line field switchboard consisting of two 0-line boards During low traffic conditions only one operator may be required, and in such case all cord pairs can be connected to the speaking equipment of one board. This facility can be arranged at the time of setting up the switchboards by connecting a plug-ended cord between the jacks on the rear sides of the switchboards. When one of the operators completes his period of duty, he presses the concentration key on his position set. Interference Suppression and Earthing The switchboard is equipped with interference suppressors to prevent disturbance of nearby radio stations. The components for which interference suppressors are required are the pole changer, dial, hand generator and bell. For effective interference suppression the switchboard must be earthed. Shock and Drop Tests The switchboard has been subjected to a very severe shock test with an acceleration of 0 g along the three main axes. No serious faults were revealed. This test was performed in order to ascertain the ability of the switchboard to withstand the shocks it may be exposed to under rough transport conditions. The object of the drop test was to find out particularly whether the casing provides adequate protection against careless handling when loading onto and unloading from a truck. The switchboard was allowed to drop freely from a height of metre onto a floor of cm thick planks butted to a concrete floor. The test was repeated three times on different sides of the switchboard. The switchboard suffered no damage such as to jeopardize its function. Climatic Tests The switchboards have stood up satisfactorily to comprehensive cold, heat and moisture tests. The new design of cord winder has been subjected to severe wear tests, to which it has stood up satisfactorily.

65 NEWS/rom ll Quarters of the World Tunisian Minister of Communications Visits L M Ericsson nother Large Ericsson Order from Colombia contract has been signed between L M Ericsson and Empresa de Telefonos de Bogota, the telephone operating company in the capital of Colombia, for telphone exchange equipment to a value of about million Kronor. The bulk of the equipment, which is of crossbar type, will be used for new exchanges in the Bogota area. Old exchanges are also being re-equipped, so that the Bogota telephone network as a whole will be brought thoroughly up to date. The first contract between Empresa de Telefonos de Bogota and L M Ericsson was for lines in. fter installation of the equipment now on order Bogota will have a total of 000 dial lines, all supplied by L M Ericsson. Bogota is now fourth South merican city in number of telephones. L M Ericsson has also signed contracts with Colombia for extension of the telephone plants at rmenia, Cartagena, Ibague, Pasto and Santa Rosa de Cabal, for a total amount of over million Kronor. The Tunisian Minister of Communications, Rachid Driss, also head of the P.T.T., made a semi-official visit to Sweden at the end of February, accompanied by his wife and the Technical Director of the Ministry of Communications, Mohamed Mili. His very full programme included a visit to the L M Ericsson factory at Soderhamn and, of course, to the head factory in Stockholm. The - year-old Minister journalist by profession and Minister of Communications since did not confine his interest to the technical side of production but posed a multitude of questions also on welfare conditions, unemployment problems, the status of women, etc. Minister Driss also visited the Midsommarkransen factory and Ericsson Kindergarten. He is seen below with his wife at a round table conference with the children. Tunisia is at present one of L M Ericsson's main markets and, since, has purchased about million Kronor's worth of equipment. By the end of L M Ericsson expects to have some 000 lines in service in Tunisia. The installations at present on order are expected to be completed by. The photograph above shows a group examining a 00-line switch at the Soderhamn factory. (From left) Sven T berg, president of L M Ericsson, Minister Driss, Gosta Skoglund, Swedish Minister of Communications, Mohamed Mili, and L M Ericsson engineer Rune Hiiggo.

66 (Left) Exterior view of the factory at Sao Jose dos Campos. (Below) The forming of cables in the factory. the factory was extended to an area of 000 sq. ft., and again in 0 to the present sq. ft. Originally the factory produced telephones only. fter the first extension, work started on the assembly of crossbar switches, cable forming, wiring and testing of crossbar racks. The work has now progressed to the assembly, cabling and testing of relay sets, manual switchboards, trunk boards, and P..X. Ericsson Factory in Brazil to be Extended The Ericsson factory in Brazil lies on the autostrada between Rio de Janeiro and Sao Paulo, at Sao Jose dos Campos, about 0 miles from Sao Paulo. It was completed in and has since between twice extended. It today employs about 00 persons, but next year the number is expected to have increased to 00. Work on the first part of the factory, covering an area of 000 sq. ft., started in. The architect was Oscar Niemeyer. Niemeyer is considered one of the world's foremost architects and is co-creator of most of the public buildings in the new capital, Brasilia. The factory was officially opened in. The inauguration ceremony was attended by persons from all parts of Brazil and was surrounded by considerable publicity, which added to Swedish good will in Brazil. In the same year Manufacture of crossbar switch parts has already started, and by the autumn the first Brazilian-produced switch will have been completed. bit later will come the first RF relay. Except for certain specialized parts and cable, the entire manufacture will by then be located in Brazil. Products are regularly sent to Stockholm for testing, and the Brazilian quality has been found to be fully comparable with that from Swedish factories. North Electric Provides Controls for Big Pipeline North Electric Company of Galion, Ohio, has been awarded a major contract by Mid-Valley Pipeline Company, Longview, Texas, for the complete modernization of the latter's pipeline facilities by installation of automation controls on all pump stations in the system. North Electric will provide "Paricode" supervisory control and telemetering equipment to automate Mid-Valley's 0-mile pipeline network from Longview to Lima, Ohio. Upon completion of this programme, Mid-Valley will have one of th? largest automated crude oil pipelines in the world. Mid-Valley is a 0-inch and -inch crude oil common carrier pipeline, interconnecting with other carriers in the Southwest and Midwest. Supervised indications, alarms and field data quantities will be telemetered back to the central control station, also North-designed, providing the dispatcher with the necessary information to maintain optimum pipeline operating conditions and to take corrective action, if and when necessary.

67 The Swedish Institute in Rome is devoted to archaeological research. Twenty years ago the Institute acquired a fine building through contributions from the Swedish and Italian governments and a number of private donors. mong the latter, whose names are recorded on the memorial tablet recently unveiled by the King of Sweden, is Telefonaktiebolaget L M Ericsson, which, in cooperation with SIELTE, presented a modern telephone installation for the use of the Institute. In the middle of February Egypt's first Ericsson crossbar type city exchange, the bbassia exchange, was cut over in the presence of, among others, Dr. Mahmoud Mohamed Riad, Director General of the United rab Republic Telecommunications Organization (URTO). In the photograph below, taken during the reception following the opening ceremony, are seen (from left) mbassador Sven Dahlman, Mr. Sven T. berg, Dr. Riad and the Minister of Communications. Mostafa Khalil. (Below right) In conjunction with the 0-year jubilee of Ericsson's French subsidiary, Societe des Telephones Ericsson, the board of L M Ericsson and a number of selected guests visited the teliers Vaucanson factory at St. Nicholas. (From left) G. Forssius, Swedish Consul General in Paris, Vice dmiral E. nderberg, H. Lindberg, VV. Soderman, E. Browaldh, Dr. M. Wallenberg and mbassador E. Boheman. The Director General of the Jugoslavian Railways, Vojin Nicolic, on a visit to the main Ericsson factory in Stockholm, was shown the newly established Language Laboratory. (From right) Director General Nicolic, Erik Lundquist, I. Veselic, Svetislav Miladinov, L. Sekulic, Secretary of the Jugoslavian Embassy, and N. Kallerman and H. Insulander of L M Erics-

68 Copenhagen Exchanges to be Equipped with Code Switches round the turn of the century the Copenhagen Telephone Company introduced the so-called Copenhagen system, the idea of which was to concentrate all subscribers with a high calling rate to a single exchange called Central. The time is now ripe for a change, and the Central exchange subscribers are being successively transferred to the automatic district exchanges to which they belong geographically. The roughly subscribers resident in the central area will in due course be transferred to the new all-automatic exchanges which the Copenhagen Telephone Company is building on Norregade. These exchanges are being equipped with the L M Ericsson code switching system. This system offers certain advantages to the transferred subscribers since they can retain their four-digit numbers with the addition of a two-digit prefix. The Ericsson code switch is considered one of the foremost inventions in Swedish telephone engineering in recent years. part from the Copenhagen Telephone Company, the Swedish Telecommunications dministration has ordered a plant for initially 000 lines for the new suburban exchange at Drevviksstrand. and from Italy orders have been received for line concentrators serving a total of 000 lines. The main feature of the new system is its compactness of structure. The code switch has a larger capacity but requires far less space than the crossbar switch. It also permits a different method of construction, with the racks suspended on ceiling girders placed side by side like books on a shelf. ll relay sets and switching units are detachable and can be plugged in after the racks have been assembled. The exchange cabling is placed on the floor under the racks instead of, as hitherto, on runways above the racks. Installation work is thus greatly facilitated. The compact structure of the code switch is due to two factors. The first is that wire springs have been used instead of leaf springs in the multiple; and the second is the use of an entirely new system of selection. This has enabled the number of magnets per vertical unit to be halved although the capacity of the vertical has been doubled. Out-of-the-way Ericsson ssignments L M Ericsson has people at work throughout the world. Two places to which few find their way in the normal course of events are the Libyan desert and the Himalayas, where Ericsson engineers were engaged on telephone exchange construction during the summer and autumn of. 00-line crossbar exchange type RF 0 has been built in the El Beida oasis, and a new 000-line automatic exchange at Katmandu in Nepal. The pioneering work at El Beida new capital of Libya was started in May last year. part from the local exchange, L M Ericsson has supplied a manual trunk centre, which was cut over at the same time. t Katmandu two Ericsson engineers have been serving as instructors to the Nepalese during the past years. For more than one year they have been teaching the art of using electricity, soldering, connecting and splicing cables; and the mysteries of circuitry have been taught in the schoolroom. ll this schoolwork has prepared the way for the construction of the outside plant and for the installation and testing of the new automatic exchange equipment. (bove) Two Nepalese working on the installation of the new Katmandu exchange. (Left) The first parts for the new exchange at El Beida being unloaded after arrival at the 0

69 UDC.. LME HLLBERG, P- & SCHILLING, H: Transistorized Group Translating Equipment for Carrier Terminals. Ericsson Rev. ():, pp.. This article is associated with the description of the channel translating equipment for carrier terminals given in Ericsson Review No.,. In addition to the group translating equipment the description covers the pilot-controlled level regulation of the basic group and also an equipment for signalling blocking when there is a break in the transmission path. UDC.. LME 0 RPP, Y: Planning of Multi-exchange Networks with aid of a Computer. Ericsson Rev. ():, pp. 0. The planning of multi-exchange networks may involve extremely extensive numerical calculations. This applies especially to problems of determining the number of exchanges, their locations and boundaries, the traffic distribution between exchanges after modification of the network structure, and finally to the allocation of junctions between direct and tandem routes. To simplify this work. L M Ericsson has developed methods which permit programming of the most laborious operations for an electronic computer. The questions of exchange locations and boundaries, and the traffic between the exchanges are dealt with briefly. The question of the structure of junction circuits will be dealt with later. Detailed discussions of these problems will be published shortly in Ericsson Technics. UDC.. LME BJORKMN, T: Portable 0-line Switchboard. Ericsson Rev. ():, pp.. L M Ericsson has produced a 0-line portable switchboard which not only has the robustness and full telephonic facilities required for use in the field, but also meets the condition essential in field telephone equipment, that it shall not cause disturbance to radio stations even if located in its immediate vicinity. The switchboard was designed in close collaboration with the Swedish rmy Ordnance dministration.

70 The Ericsson Group ssociated and co-operating enterprises E U R O P E Denmark L M Ericsson /S Kobenhavn F, Finsensvej $, lei: Fa, tgm: ericsson Telefon Fabrik utomatic /S Kobenhavn K, maliegade, tel; C, tgm: automatic Dansk Signal Industri /S Kobenhavn F, Finsensvej. tel: Fa, tgrn: signaler Finland O/r LM Ericsson /B Helsinki, Fabianinkatu, tel:, tgm: ericssons France Societe des Telephones Ericsson Colombes (Seme), Boulevard de la Finlande,tel:CHrlebourg -00, tgm: ericsson Paris e. Rue de Courcelles, tel: CRnot -0, tgm: eric teliers Vaucanson, Pons XX, B. P..0,tel: MENILmontant -0, tgm: atelcanson Great Britain Swedish Ericsson Company Ltd. London, W. C., ; High Holborn, tel: Holborn 0, tgm: teleric Production Control (Ericsson) Ltd. London, W. C., High Holborn, tel: Holborn 0. tgm: productrol holb Italy Setemer, Soc. per z. Roma, Via G. Paisiello -, tel:.,., tgm: setemer SIELTE, Soc. per z. Roma, C. P. 0 ppio, tel: 0, tgm: sielte F.. T. M. E. Soc. per z. Roma, C.P. 0 ppio, tel: 00, tgm : fat me gencies. EUROPE Belgium Electricite et Mecanique Suecioises Bruxe//es, Rue de Stassart, tel:, tgm: electrosuede Greece "ETEP" S.. Commerciale & Technique thens, Rue Lycavittou, tel: 0, tgm: aeter-athinai Iceland Johan Ronning H/F Reykjavik, P. O. B., tel: 0. tgm: ronning Ireland Communication Systems Ltd. Dub/in, Pembroke Road, Ballsbridge, tel: 0 tgm: crossbar Yugoslavia Merkantile Inozemna Zastupstva Zagreb. PoSt pretinac, tel:, tgm: merkantile, telex: 0- SI Burma Burma siatic Co. Ltd. Ericsson DepartmentRangoon. P.O.B. 00, tel: 0, tgm: ericsson Cambodia The East siatic Company Ltd. Phnom-penh, P.O.B., tel: Central 00, fgm : plandep Ceylon Vulcan Trading Co. (Private) Ltd. Colombo,, York Street, tel: -, tgm: vultra China The Ekman Foreign gencies Ltd. Shanghai. P. O. B., tel: -, fgm: ekmans Netherlands Ericsson Telefoon-Maatschappij, N.V. Riien (N.Br.), tel: 0-, tgm: erictel den Haag Schcveningen, 0, Palaceslraat, tel: 00, tgm: erictel-haag Norway /S Elekiriijk Bureau Oslo NV.P.B. 0, tel: Centralbord 0, tgm : elektriken /S IndustrikontroM Oslo, Tealergcten,tel: Centralbord 0, tgm: indtroll /S Norsk Kabelfabrik Drammcn, P. B. 0, tel;, tgm: kabel /S Norsk Signalindustn Oslo, P. B. Mj, tel: Centralbord, tgm: signalindustri Portugal Sociedade Ericsson de Portugal, Lda. Lisboa,, Rua Filipe Folque, tel:, tgm: ericsson Spain Cia Espanola Ericsson. S.. Madrid, Torre de Madrid cr piso, oficina. Plaza de Espafia, tel : 00, tgm : ericsson Sweden Telefonaktiebolaget L M Ericsson Stockholm. tel: 00 00, tgm: telefonbolaget B lpha Sundbybcrg, tel:00, tgm: akliealpha-stockholm B Ermex Solna, tel: 000, tgm: elock-stockholm BErmi.Karlskrona, tel: 00; tgm: ermibolag-karlskrona B Rifa Bromma J, tel: 0, tgm: elrifa-stockholm B Svenska Elektronror Stockholm 0, tel: 0 0, tgm: electronics L M Ericssons Driftkontrollaktiebolag Solna. tel:, tgm: powers-stockholm Hong Kong The Swedish Trading Co. Ltd. Hongkong. P. O. B. 0, tel: -S, tgm: swedetrade Iran Irano Swedish Company B, Teheran, Khiabane Sevom Esfand, tel:, tgm: iranoswede Iraq Koopman & Co. (Iraq) W.L.L. Baghdad, P. O. B., tel:, tgm: koopiraq Japan Gadelius & Co. Ltd. Tokyo C, P. O. B., tel: 0-, tgm: goticus Korea Gadelius & Co. Ltd. Seoul. I. P. O. Box, tel:. tgm : gadeliusco Kuwait Latiff Supplies ltd. Kuwait, P. O.B., tgm : lalisup Lebanon Swedish Levant Trading (Elie B. Helou) Beyrouth, P. O. B., tel:, tgm: skefko Pakistan Vulcan Industries Ltd. Karachi City, P. O. B., tel: 0, tgm: vulcan Philippines USI U.S. Industries Philippines Inc. Manila P. R., P. O. B.. tel: --, tgm: usiphil Saudi rabia Mohamed Fazil bdul la rab Jeddah, P. O. B.. tel: 0, tgm : arab Singapore and Malaya The Swedish Trading Co. Ltd. Singapore, Chartered Bank Chambers, Baltery Road, tel:, tgm: swedetrade Syria Georgiades, Moussa & Cie Domas, Rue Ghassan, Harika, tel: -0-, tgrn: georgiades L M Ericssons SignalaMiebolag Istanbul, ^^^^^^^H^H Stockholm Sv, tel: 0 00, tgm: Han, Kat signalbolaget tel: 0, tgm: ellemisl L M Ericssons Svenska Fbrsaljningsaktiebolag Stockholm, Box. tel: 00, tgm: ellem Mexikanska Telefonaktiebolaget Ericsson Stockholm, tel: 0000, tgm: mexikan Sieverts Kabelverk B Sundbyberg, tel: 0, tgm: sievertsfabrik-stockholm Svenska Radioaktiebolaget Srocfcholm, lstromergatan, tel: 0, tgm: svenskradio B Ostmarks Ldsfabrik Eskilstuna, Munktellsgatan, tel: Switzerland Ericsson Telephone Sales Corp. B, Stockholm, Zweigniederlassung Zurich Zurich, Postfach Zurich, tel:, tgm: telericsson West Germany Ericsson Verkaufsgesellschaft m. b. H. Dusseldorf, Postfach. tel:, tgm: erictel SI India Ericsson Telephone Sales Corporation B New Delhi, P.O.B.. reg.mail: / saf M Road (Delhi Estate Building), tel:, tgm: inderic Calcutta, P. O. B., tel: -, tgm: inderic Indonesia Ericsson Telephone Sales Corporation B Bandung, Djalan Dago. tel:, tgm: javeric Djakarta, Djalan Gunung Sahari, tel: Kota, tgm: javeric Lebanon Telefonaktiebolaget L M Ericsson, Technical Office Beyrouth, Rue du Parlement, Immeuble Bisharat, tel:, tgm: ellem Thailand Ericsson Telephone Sales Corporation B, Bangkok, P. O. B., lei:, tgm: ericsson Turkey Ericsson Turk Ticaret Ltd. SJrketi nkara, dii Han, Zafer Meydani, Yenisehir, tel: 0, tgm: ellem Thailand Ericsson gency Office, Telephone Organization of Thailand Bangkok, Ploenchitr Road, tel:, tgm: telthai Vietnam Vo Tuyen Dien-Thoai Viet-Nam, Saigon, Dai-lo Thong-Nhut, tel: 00, tgm: telerad FRIC British East frica Transcandia Ltd. Nairobi, Kenya, P. O. B., tel:, tgm: transcanda Congo (Fed. Rep.) Society nonyme Internationale de Teldgraphig sans Fil (SIT) Bruxelles (Belgique),, Boulevard du Regent, tel: 00. igm: wireless (For marititn radio and carrier) Ethiopia Swedish Ethiopian Company ddis baba, P. O. B., tel:, tgm: etiocomp Ghana The Standard Electric Company ccrd, P.O.B., tel:, tgm : standard Liberia Swedish gencies Liberia Co. Monrovia, P.O.B. 0, tel:. tgm: salco Libya The Gulf Trading Co. Tripoli, P.O.B., tel:, tgm: gultraco Mauritius Mauritius Trading Co. Ltd. Pott Louis, P.O.B. 0. tgm:agentou Morocco Elmar S.. SEYRE Tangier, Francisco Vitoria,, tel: -0. tgm: elmar FRIC Egypt (UR) Telefonaktiebolaget LM Ericsson, Egypt Branch Cairo, P. O. B.. tel:, 0, tgm: elleme Rhodesia LM EricssonTelephoneCo. (Ply) Ltd.(Branch Office of LM Ericsson Telephone Co. Pty. Ltd. in Johannesburg) Salisbury, Sou/hern Rhodesia, P.O.B., tel: 0 0. tgm: ericsson Republic of South frica L M Ericsson Telephone Co.Pty. Ltd. Johannesburg, Tronsvoai, P. O. B. 0. tel: -, tgm: ericofon Tunisia Telefonaktiebolaget LM Ericsson, Technical Office Tunis, Boite Postale 0. tel: 00, tgm: ericsson. MERIC rgentine Cia Ericsson S.. C. I. Buenos ires, Casilla de correo 0,tel: 0, tgm: ericsson Cia rgentina de Telefonos.. Buenos ires, Peru, tel: 0 0, tgm: catel Cia Entrerriana de TeleTonos S.. Buenos ires, Peru, tel: 0 0, tgm: catel Industrias Etectricas de Quilmes S.. Qu//mes FCNGR, de Octubre 00, tel: 0-, tgm: indelqui-buenosaires Brazil Ericsson do BrasiI ComeVcio e Industria S.. Rio de Janeiro, C. P. 0, tel: -00, tgm; ericsson Sao Paulo, C. P., tel: -, tgm: ericsson Canada LM Ericsson Ltd. Montreal, P.O., 00 Laurentian Boulevard, City of St. Laurent, tel: 0, tgm: caneric Toronto. Ont., P. O. B., tel: BE -0 Chile Cfa Ericsson de Chile. S.. Sonf/ago, Casilla 0, tel:, tgm: ericsson-santiagodechile Mozambique i. Martins Marques Lourer.co Marques, P. O. B., tel:, tgm : tinsmarques Nigeria I.P.T.C. (West frica) Ltd. Lagos, P.O.B. 0, tel:, tgm: consult Sudan TECOM Technical Consulting and Machinery Co. Ltd. Khartum, P.O.B., tel:, ext., tgm: sutecoma MERIC Bolivia Johansson & Cia, S.. La Paz, Casilla, tel: 00, tgm: Johansson Costa Rica Tropical Commission Co. Ltd. San Jose, partado. tel:, tgm: troco Cuba Mc voy y Cia Habana, partado, tel: -, tgm: macavoy Curacao N. W. I. S. E. L. Maduro & Sons, Inc. Curacoo, P. O. B.. tel: 00, tgm: rnadurosons-willemstad Dominican Republic Garcia & Gaulier, C. por. Sairo Domingo, partado, tel:, tgm: gartier Guatemala Nils Pira Ciudad de Guatemala, partado, tel:, tgm: nilspira-guatemala Hondur Quinchc" galpa, tgm: qu iaao /M.'i tu -luj*, I = I. -ii' tgm: ericsson Ecuador Telefonos Ericsson C.. Quit* Casilla, tel: 00, tgm ericsson Guayaquil, Casilla, tel: fgm: ericsson Mexico TeleTonos Ericsson S.. Me»,C( D.F., partado, tel: < tgm: coeric Industria de Telecomunicacio S.. de C.V. MeWco, D.F., Lond res No., tel: 00, tgm: i dustel Peru Cia Ericsson S.. Lima. partado, tel:. tgm: ericsson Soc. Telefonica del Peru, S., i requipa, Casilla de Correo J tgm: telefonica El Salvador Telefonaktiebolaget LM Ericsson, I Technical Office, San Salvador] partado Postal, tel: [ tgm: ericsson Uruguay Cia Ericsson S.. Montevidto, Casilla de Correo, tel: -- ', tgm: ericsson US The Ericsson Corporation New York, N. Y., 00 Park venue tel: Murray Hill -00, tgm: erictel North Electric Co. Gallon, Ohio, P. O. B., tel: Howard -0, tgm: north p ho ne-galionohio Venezuela Cia nnima Ericsson Caracas, partado, tel:, fgm: ericsson TeleTonos Ericsson C.. Caracas, partado, tel:, tgm: tevela USTRLI & OCENI ustralia L M Ericsson Telephone Co. Ply. Ltd. Me/bourne C (Victoria), 0 Collins Street, tel:, tgm: ericmel L M Ericsson Trimax Pty. Ltd. CoburgN (Victoria). P.O.B., tel: 0, tgm; trimax Jamaica and Brit. Honduras Morris E. Parkin Kingston, P.O.., tel: 0, tgm: morrispark Nicaragua Edmundo Tefel Managua, D.N., partado Postal, tel: 0, tgm: edfelco Panama Productos Mundiales, S.. Panama. R. P., P. O. B., tel: -0, tgm: mundi Paraguay S.. Comercial e Industrial H. Petersen suncion, Casilla, tel:, tgm: pargtrade Puerto Rico Splendid Inc. Sin Juan, P. 0. B., tel: -0, tgm: splendid El Salvador Dada-Oada & Co. San Salvador,] partado, tel: 0, tgm:; dada Surinam C. Kersten & Co. N. V. ParM manbo. P. O. B. C. tel:,] tgm: kersten Trinidad, W. I. Leon J che Ltd. Porl-of-Spoin, 00 Frederick Street, tel:, tgm: achegram US Clark Walter Corporation Ne*J ark, N. J., Broad Streflff tel: Mitchell -, tgm: w\rm walter-newarknj. (For jntercobjj State Labs. Inc. New York, N. V Pc^k venue South, tel: Ore-r gon -00, tgm: statelabs (F r electron tubes). USTRLI & OCENI*

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73 ERICSSON REVIE Vol. XXXIX No. RESPONSIBLE PUBLISHER: HUGO LINDBERG EDITOR: SIGVRD EKLUND, DHS EDITOR'S OFFICE: STOCKHOLM SUBSCRIPTIONS: ONE YER $.0; ONE COPY $ 0.0 CONTENTS n Experimental Data Transmission System page Crossbar P..B.X. RD Duration Meter VMF L M Ericsson News from Quarters of the World ll 0 On cover: Operator's console for L M Ericsson's P..B.X. RD COPYRIGHT TELEFONKTIEBOLGET LM ERICSSON PRINTED IN SWEDEN, ESSELTE B, STOCKHOLM

74 n Experimental Data Transmission System WWIDL, T E L E F O N K T I E B O L G E T LM ERICSSON, STOCKHOLM UDC.. LME During the last few years technical development has entailed an everincreasing demand for the transmission of vast amounts of data between geographically separated centres. Particularly military defence systems are in urgent need of data transmission equipment permitting higher speeds. It is therefore natural that the system described below should have been developed to the order of Kungliga Flygforvaltningen (the Royal Swedish ir Force dministration), which also drew up the required basic specification. This resulted in the construction of a phase-shift data transmission system permitting the transmission of binary digits at a speed of up to 00 bauds over telephone circuits. In the following chapters a description will be given of the function and construction of the system. In conclusion a few test results are given.. General Information on Data Transmission The fields of application for data transmission systems are manifold, and may be illustrated by means of the following two simple examples. To simplify the replenishment of supplies, each branch of a multiple firm sends a list of required goods to the main office every evening. The data transmission system applied for this purpose is only used for a short length of time, but for the transmission of a large amount of information. The transmission may for instance be carried out over a switched telephone connection. The traffic on a railway line is controlled by data regarding train movements, switch positions, etc. In this case the data transmission system operates continuously. Its great transmission capacity is necessary to keep the traffic supervisor informed about the situation. By its nature the system requires a leased telephone connection. s the examples show, a data transmission system always co-operates with data-handling equipment in some way. complete system, comprising data-handling equipment, control and checking circuits, receiving and transmitting devices as well as data transmission systems, is called an integrated data system. Obviously it will be profitable to standardize the inputs and outputs of the data transmission system as well as their operating principles to make it possible to use them in various integrated data systems. Proposals for a solution of these standardization problems arc under discussion in the CCITT Special Study Group. Thus the equivalence has been declared between: Binary digit = "Mark" = positive current in the case of bipolar signals = = condition Z Binary digit 0 = "Space" = negative current in the case of bipolar signals = = condition n effective data transmission system should meet the following requirements: high speed low vulnerability to noise and pulse interferences low vulnerability to distortion in the transmission path concentrated signal spectrum on the line simple as well as economic terminal composition When designing a system the above factors will give rise to a series of compromises closely related to the transmission line employed. From an economic point ot view it is advantageous to use for data transmission those

75 Fig. Pulse shaping X Fi(t) Pulse shape > Incoming signal Si(f) mplitude spectrum FB(t) Pulse shape Signal after pulse S..(f) mplitude spectrum I shaping T^ Bit period h Bit frequency -Tb 0 Tb 0 0fb telephone and telegraph networks which already exist. When these networks were designed, however, in most cases no regard was paid to the special requirements as to the phase and attenuation conditions of the network for data transmission. The line distortion will limit the transmission speed of the system and its resistance to interferences. Consequently, if data are transmitted over leased telephone circuits, it is advantageous to compensate for the distortion by means of equalizing networks. This is not possible in the case of switched telephone connections, because apparently it is not economic to equalize all types of telephone circuits in one network. In that case it is essential to choose the appropriate modulation and detection methods to obtain compensation for the decrease of the circuit quality. Fig. Data transmission system, sender Fp Pulse-shaping filter Fi Intermediate-frequency filter F Low-pass filter G, LC-Oscillator (. ke/s) G: LC-Oscillator (. kc/s) R. Rv Frequency divider Gj< Quartz crystal oscillator ( kc/s) i Output amplifier DS Pad Kl Clock-pulse generator Mi, Mo Modulator. Basic System When designing the data transmission system developed by L M Ericsson, special attention was given to the desirability of having a concentrated signal spectrum on the line in order to reduce the need for equalization as much as possible. This has resulted in a system which uses phase-shift modulation together with special pulse shaping at the sending end and synchronous demodulation and pulse regeneration at the receiving end. With the aid of figures and, a detailed description will be given of the function of the system at a transmission rate of 00 bauds. For the sake of simplicity the internal group delays of the system have been ignored in these figures. Block diagram for transmitter Clock pulses Bipolar fb = 00 c/s data signal Waveforms of data signal Frequency spectra of data signal t[ms] 0. h t [kc/s] n Phase-shifl data signal ra J *.0

76 Saving band width by pulse shaping In the transmission of information a data flow in the form of a bipolar signal is fed to the sending terminal of the data transmission equipment. n incoming "" (E) is for instance represented by a positive square wave current pulse and a "0" (N) by a negative square wave current pulse. The data flow can be considered as consisting of a series of positive and negative pulse elements or bits. To obtain an idea of the pulse shaping a single positive square wave is studied (fig. ). The pulse contains a wide pulse-frequency spectrum, which is limited and shaped in a pulse-shaping filter with a cut-off frequency corresponding to half the bit frequency (the bit frequency /,, denotes the reciprocal of the bit period, /,, (c/s) = /T,, (sec. ). Thus, at a data speed of 00 bits/second the spectrum is concentrated to about 00 c/s bandwidth (baseband). In passing through the low-pass filter the square wave is converted into a pulse whose form can be represented as sin x/x, showing a peak at the middle of the pulse and zero crossings at intervals equivalent to multiples of the bit period as measured from the middle of the pulse. If in a message bits are transmitted at a speed of /,,. the sin x/.v-pulses will likewise occur at intervals equivalent to multiples of the bit period i. Therefore, we may state that every pulse peak coincides with the zero crossings of the adjacent pulses. When the filtered pulse elements are scanned in the middle of the bit. amplitude values will be obtained which are independent of the polarity of the adjacent bits. Modulation at the sending end fter pulse shaping in filter F p (fig. ) the signals will cover a frequency band of 0-00 c/s, a band which owing to its position is unsuitable for transmission over telephone channels. By means of a balanced modulator M, and a first carrier frequency, a double-sideband signal is generated which covers a frequency band of.-. kc/s. Fig. shows the circuit diagram of the modulator. In step with the carrier frequency either circuit ^D^-D or circuit / X -D -D is closed. Thus, either path -D - or path ^-D^-., is opened for the data signal. fter modulation the intermediate-frequency band signal has an envelope which is equal to the baseband wave form at the modulator input, and a carrier phase depending on the polarity of the baseband signal. change of the signal polarity in the baseband will produce a 0 phase shift in the carrier in the intermediate-frequency band. This is why this type of modulation is termed "phase-shift modulation". The modulated signal passes through an intermediate-frequency filter, which eliminates higher modulation products. In a further modulation stage comprising modulator M and oscillator C. a second carrier frequency is added which translates the data signal to the line band, the envelope and phase relations remaining unchanged. fter filtration and amplification the data signals are transmitted over the line. The line frequency band used for this purpose is about 00 c/s, so that the present data transmission system requires for transmission a frequency band which is only slightly higher than the bit frequency. Demodulation at the receiving end On their way to the receiver the data signals are exposed to line distortions and interferences. t the receiver input a high-pass filter eliminates l.f. pulse interferences, e.g. interference from d.c. signalling on adjacent telephone wires. The correct receiving level is ensured by means of a regulating amplifier, which stabilizes the signal level. subsequent limiter reduces the disturbing effect of transient pulses which exceed a certain voltage threshold. Fig. shows a distortionless received signal which is modulated in modulator M : with carrier frequency f./. The subsequent intermediate-frequency filter matches the width of the signal spectrum and attenuates interference

77 Block diagram for receiver Waveforms of data signal DS F- t[ms] Fig. X Data transmission system, receiver DS Pad F High-pass filter a Regulation amplifier B Limiter M,Mi Modulator G. LC-Oscillator (. kc/s) F^ Intermediate-frequency filter (.. kc/s) DL Full-wave rectifier F Band-pass filter (.. kc/s) R, Rv Frequency divider D y Delay circuit F, Low-pas, filter (. kc/s) G^ Quartz crystal oscillator ( kc/s) L Logic circuit N Zero-crossing detector Limiter amplifier Det mplitude detector P Pulse regenerator Reg Carrier regenerator kl Clock-pulse regenerator Fig. cceleration period Clock-pulse generator I SF-0-~ s n ;' mrpf Clock r r pulses I^L.EIil output J Retardation period G^ Quartz crystal oscillator Rv Frequency divider d Pulse differentiation circuit Li, Lj, h, nd-circuit L, Or-circuit Fa, Fd Flip-flop IV Zero-crossing detector R Frequency divider (Binary counter) Clock-pulses fb = 00 c/s Bipolar data signal occurring outside the signal band. Owing to frequency differences between f and f ' as well as the effect of frequency drift in the transmission of signals over carrier channels it is not possible to demodulate the signal in the intermediate-frequency band with a fixed carrier frequency //. On the other hand, the signal contains a spectral component which permits regeneration of the carrier frequency necessary for synchronous demodulation. By full-wave rectification and selection of the double carrier frequency /,' in a narrow band-pass filter an exact reference frequency, independent of data, is obtained. fter a frequency divider and a delay circuit the correct carrier frequency is obtained, occurring in two possible phase positions, or B, having a phase shift of 0. If a distortionless signal is demodulated in modulator M, by means of carrier frequency /,' in phase position, a data signal which is equal to the sender baseband signal after pulse shaping will be obtained after filtration. If, on the other hand, the demodulation is carried out in phase position B, the polarity of the regenerated signal will be changed, resulting in a transmitted "" being perceived as a "0", and vice versa. (The signals are inverted). In chapter a description will be given of two possible means of eliminating ambiguity in transmission. Regeneration of the d. c. signal If, after demodulation and amplification in the limiter amplifier, the data signal is scanned in the middle of each bit, the information contained in the signal element is obtained from the polarity of the amplitude. Therefore, it is essential to regenerate the bit frequency in the first place. If the data flow ensures a certain number of polarity changes per number of transmitted bits, the zero crossings can synchronize a clock-pulse generator that generates the bit frequency. Fig. shows the operating principle of a quartz crystal controlled clock-pulse generator. quartz crystal oscillator G k ( kc/s) drives a -step ring counter via a frequency divider R, and logic circuits L, and L. clock-pulse f-, is produced after every cycle of the ring counter. Flip-flop (toggle) F a is driven from counter R and is in the "acceleration condition" during the time f : to f and in the "retardation condition" during the time f to f - If a zero crossing occurs under the acceleration condition the synchronizing pulse is led from the zero-crossing

78 detector JV over logic circuits L :t and L., direct to the input of the ring counter. The revolution period of the counter is diminished by l /s during one cycle. During the retardation period a synchronizing pulse will block the path via flip-flop F, differentiation circuit d and logic circuit L, for one of the pulses proceeding from the quartz oscillator. Thus the revolution period of the ring counter is increased by " during one cycle. If no zero crossings occur the revolution period of the counter will not change. In the detector every bit is scanned in the middle by means of the regenerated bit frequency. repeating flip-flop will reproduce the data signal in the form of square waves.. Use of the System s was mentioned in the preceding pages, a data transmission terminal is connected to a transmission system as well as to a data-handling equipment. In order to facilitate the matching of the data signals to the lines their spectra can be shifted by changing the oscillators G L, of the data transmission terminals. line connection over a loaded cable, for instance, requires a signal spectrum shift to 0.. kc/s. This is obtained when /., =. kc/s. The flexibility in relation to the data-handling equipment is increased by the possibility of altering the bit frequency by means of frequency divider R,. which is variable in steps. To achieve the best possible pulse shaping and interference elimination, the pulse-shaping filter of the sender and the intermediate-frequency filter of the receiver have to be changed when the bit frequency is changed. System using differential coding Data transmission systems using differential coding are particularly suitable for continuous transmission between data-handling equipment provided with buffer stores. In order to eliminate ambiguity in demodulation a differential coding equipment is inserted between the data-handling equipment and the data transmission equipment. t the sending end a "0"-voltage at the input of the encoder will result in a polarity change in the middle of the bit at the encoder output, whereas a " "-voltage will not affect the output voltage of the encoder (see fig. ). With the aid of an external or internal bit-frequency clock-pulse generator a data flow (0, ) is read out from the data-handling equipment and fed to the encoder, which in its turn produces a data signal (N. E). The output signals of the encoder will pass through the data transmission equipment outlined in figs. and and. when demodulated in phase position, will P DBS Ko Data signal Clock pulses Differential - coding data -- u n^^^f- Fig. Data transmission system using coding DBS Data-handling sender QBM Data-handling receiver P Pulse regeneration Ko Encoder De Decoder Kl Clock-pulse regeneration Kle External or internal clock-pu se generation DTS Data transmission sender DTM Data transmission receiver X differential KL DTS Kl \ Distortion^ line t OTM De ' DBM ss Differential coding data signal Clockpulses Data signal I E N EE Phase position B J ^^^thzftftr' pb

79 result in signal P, whereas when demodulated in phase position B a signal Pn will be produced. If two pulse elements of different polarity occur in succession at the input of the receiver decoder a "0"-voltage will be generated at the output during one bit period. Two pulse elements of the same polarity will produce a " "-voltage at the output. Consequently, the output signal of the decoder is independent of whether the modulation is carried out in phase position or B and corresponds with the input signal of the encoder at the sending end. In step with the regenerated bit frequency the bipolar data signal is fed to the data-handling terminal at the receiving end.

80 System using start code In certain data transmission systems, every data message is preceded by a start code consisting of a character combination (in its normal or inverted form) which does not occur in the subsequent message. The start code can therefore be used at the receiving end for ascertaining whether the modulation has been carried out in phase position or B. When position B is used a change-over switch in the data-handling receiver or a phase shifter in the data transmission receiver will invert the message which follows a start code and will thus eliminate ambiguity in reception.. The Mechanical Construction of the System Equipment construction The design of the mechanical equipment for this data transmission system follows the new L M Ericsson construction principles for transmission equipment, involving the use of miniature components in connection with the adoption of transistor and printed-wiring techniques. The sender functions are distributed among units and those of the receiver among units. Each unit contains one function, such as a filter, modulator or amplifier. To facilitate maintenance the most important units have been provided with test points for fault location at the front of the unit. The adjustment of bit speed, signal centre frequency and level is effected by means of links at the front sides of the units. The power supply for the sender and the receiver is obtained from an individual or a common mains supply unit. The alarm equipment indicates failure of the power supply and at the receiving end also the occurrence of faulty signal levels. Shelf and bay construction The units are mounted in a shelf construction developed for " wide bays. Each shelf is designed for units. horizontal connecting strip on the shelf comprises connecting links, pads, maintenance measuring points and fuses. panel on the right-hand side of the shelf is designed for the bay cabling. The units are protected by dust covers. The horizontal connecting strip, however, is directly accessible. The data transmission sender occupies one shelf (fig. ), whereas the data transmission receiver occupies shelves (fig. ).. Technical Data Miscellaneous Modulation speeds /,, Signal centre Line requirements frequencies bandwidth required Code requirements for synchronizing the clock pulse generator of the re ceiver 000 bauds 00 bauds 00 c/s 00 c/s 00 c/s 00 c/s 00 c/s switched or leased telephone lines with maximum frequency drift ± 0 c/s 00 c/s at least one 0-element per -elements

81 Tolerance to line interruption The bit frequency regeneration permits breaks of approx. Stability requirement of external clock-pulse generator mbient temperature 000 (ms) ±- 0-i-f,, (c/s) 0 C Sender Line side Data handling side data signal and external clock-pulse Output impedance Output level Input impedance Input voltage 00 ohms + dbm max. 0 dbm min. 000 ohms ± V Receiver Line side Data handling side data signal and regenerated clock-pulse Power supply Power consumption, sender receiver. System Tests Input impedance Input level Output impedance Output voltage across kilohm load + V W W 00 ohms 0 dbm max. 0 dbm min. < 0 ohms ± V V W W Most of the errors occurring in data transmission over telephone circuits are caused by pulse interference and transient interruptions. Not even a data transmission system of optimum design can prevent errors occurring in the event of interruption. If the system is given appropriate dimensions, however, good resistance to certain types of pulse interference may be obtained. The resistance to interference is reduced by group delay and attenuation distortion in the transmission path and is raised when the signal frequency band is filtered, owing to the limitation of the disturbing amplitude. In order to give the system parameters optimum design and to measure the deterioration of the transmission channel on account of phase and attenuation distortion it is advantageous to test the system by means of a reproducible type of interference, e.g. a number of tape recordings of typical disturbing pulses. It Data Data test transequipment I mission equipment Noise test circuit I Test object Fig. X Test circuit for data transmission systems DCS Data test sender DCM Data test receiver F Error analyzer DJS Data transmission sender DTM Data transmission receiver DS HY p W L BG Pad Hybrid circuit Band-pass filter, bandwidth JI (c/s) Output power meter ImW) Line Noise generator BG - % DS I* <L * if

82 is also possible to use white noise as interference. In this case it is assumed that a system with good resistance to white noise will retain this property in the event of pulse interferences. The system tests referred to here were carried out with a test circuit which permits the injection of white noise at a certain signal-to-noise ratio at the input of the data transmission receiver. The test circuit employed is shown in fig.. data test sender generates a data flow which in the data transmission sender is converted into phase-shift data signals. The signals pass through the test object, e.g. a loaded cable, which is connected via two transformers. White noise is added to the signals in a hybrid transformer circuit. band-pass filter, whose passband is wider than the signal spectrum, limits the noise signal to an effective bandwidth of J /. fter being disturbed by the noise, the signal is demodulated in the data transmission receiver and fed to the test receiver. In the test receiver the incoming messages are compared with a programmed replica of the information sent out from the data test transmitter. n error analyzer will count both the number of incoming bits and the number of erroneous bits; in this way the error probability p,. is determined. number of bits in error number of received bits Fig. 0 a Data transmission over loaded cable Error probability pc with noise interference Rmr_ X0 pt Theoretical error curve for differential coding phase-shift system p Test object, free from distortion and interference Error curves for 0,. 0 loaded cable sections Fig. 0 b ttenuation and group delay cable X of loaded By means of an output power measuring instrument both the signal power (noise switched off) and the noise power (signal switched off) are measured, resulting in the signal-to-noise ratio R at the filter output. For a comparison of theoretical and practical results a fictitious filter bandwidth, assumed as equal to /,,, is often used as a reference. The resultant normalized signal-to-noise ratio is /?,,.. average signal power R = 0 log - - ; R average noise power R 0 log -(db) b The curves in fig. 0a show error probability p, as a function of the normalized signal-to-noise ratio R lllr. Curve p, represents the theoretical value measured for the data system, assuming the occurrence of a random data flow ("random" refers to the unpredictable sequence in which "l's" and "0's" are sent out). Curve p 0 is obtained with the aid of the above-mentioned [db] H Signal width at 00 bits/sec. 0-?n ^ i / / / / // // / /, / / / / / T 0 T / T 0 0 0, ^^^"^ 0. " Frequency 0

83 \ Error probability Pe'0 [db] Signal width at 00 bits/sec. in - t - \ \ \ \ \ \ \ \ \ / / \ ( \ i \ i > ' \ T \ V \ \\ \ \ \ \ \ \ \ \ Po \ \\\ \ PSF \ \ \ \ N \ \ \ \ \ \ N / ^ T l - - > - - ' T BF PPP nns Rmr[db] Signal-tonoise-ratio -^ - "', BF I f [kc/s] Frequency Fig. a x ; Data transmission over carrier circuits Error probability pe with noise interference Pu PBF ';! Fig. b Rmr Test object, free from distortion and interference Error curves for carrier systems connected in tandem - Error curves for carrier circuit with different phase equalizers X ttenuation and group delay T for carrier circuit with different equalizers noise test circuit, if the test object is free from distortion and interference. The information used in the test will imitate a random data flow. The register of the data test sender may for instance be programmed with a random binary-digit sequence. When sending, the register is subjected to a cyclic read-out procedure; the test sender will generate a quasi-random data flow. To demonstrate the influence exterted by line distortions a further diagram has been given of the error curves that were obtained when the test object of fig. consisted of a loaded cable with attenuation and group delay values as shown in fig. 0b. The test was carried out over 0, and 0 loaded cable sections with a data speed of 00 bits/sec. In the case of 0 loaded cable sections the group delay distortion between 0. and. kc/s was equivalent to about the length of bits. Nevertheless, when /?,. = 0 :!, the resistance offered by the data transmission system to white-noise disturbances was reduced by only. db in comparison with a distortion-free data circuit. By permission of the Royal Board of Telecommunications, tests have been made over two carrier systems connected in tandem. The attenuation BF and the group delay curve i BF of the circuit are shown in fig. lib and the corresponding error curves in fig. a. To reduce the envelope delay distortion a delay equalizer is introduced which, together with the carrier system, produces the group delay curve TJ and the attenuation curve x. The curve p, shows that the resistance offered by the data transmission system to white-noise interference is increased by db when the error probability p,. = 0 ' '. Other types of delay equalizer produce the curves r and T S and p and p, respectively. s is shown by the examples, a comparatively rough group delay equalization is sufficient to improve the transmission channel considerably. To achieve curve p 0, however, an exact equalization of the group delay and attenuation is required. The test measurements carried out so far show that the L M Ericsson data transmission system has good resistance to white-noise interference. Hence, satisfactory data transmission can be obtained by using this system over telephone circuits which are subject to distortion and interference.

84 Crossbar P.. B. X. RD EILERTSEN & S KILNDER, TELEFONKTIEBOLGET L M ERICSSON. STOCKHOLM UDC.. LME The excellent performance of the crossbar switch is being increasingly ulilized for private automatic exchanges. In the last few years L M Ericsson has brought out several types of crossbar private exchanges. One of them is the P..B.X. RD presented in this article. P..B.X. RD, with capacity range 0-0 extensions and -0 exchange lines, is intended for medium-sized organizations. In its standard design it is equipped with all modern facilities both for internal and externa) traffic and, with certain supplementary equipment, can offer some valuable extra facilities such as automatic call-back, direct access, and paging. The P..B.X can be easily adapted to the organizational form of the enterprise. It operates quickly and surely with a minimum of maintenance. The extension telephones are ordinary instruments of the same type as in the public telephone system. Special instruments such as loudspeaking telephones, secretary extensions etc.. may also be connected to the P..B.X. r Fig. P.. B. X. RD

85 \ - pole outlet '? / tt # ^ ^ fe^s ; I I Selecting bar Selecting Sixth bar bar.position Normal Traffic Facilities C-position B-position Inlet Fig. X Schematic diagram of 0-line crossbar vertical Internal calls Internal calls are initiated in the ordinary way by dialling the wanted number. two- or three-digit numbering scheme may be used, according to the capacity for which the exchange is equipped. Every extension with 0 as last digit can be given priority facility by simple strapping in the exchange. priority extension can enter a circuit on which an internal call is proceeding by dialling after receipt of dial tone. warning tone is sent on the circuit to indicate that a third party is connected. The priority extension can now deliver his message or, if he wishes to speak to the called party alone, may request both parties to replace their handsets. new ringing signal is thereupon sent automatically to the wanted extension. SL SLB 0ext. Q f. f* Fig. and B stages External calls Classification of extensions The extensions may be divided into four categories as regards external traffic facilities:. Unrestricted extensions, which, in addition to calls within the local area, may also dial their own trunk calls.. Trunk-barred extensions, which may dial calls within the local area but have restricted facilities for trunk calls (see Extra Traffic Facilities).. Semi-restricted extensions, which cannot make outgoing calls but can receive incoming calls.. Fully restricted extensions, which are debarred from all external traffic and can make internal calls only. Outgoing calls To make an outgoing call the extension dials a code digit, e.g. 0, for connection to the public exchange, followed by the subscriber's number. If there are several exchange line routes, each route can have its own code digit. Outgoing calls may also be made with the operator's assistance tch LV) Baa sa^ aas SNK \- Enquiry and transfer While speaking to an external subscriber, an extension can make an enquiry call to another extension. For this purpose he dials one impulse followed by the wanted extension's number. The enquiry call cannot be overheard by the external subscriber. tch LV) FDR-CY- If desired, the extension can transfer the call to the other extension without the operator's assistance. Enquiry or transfer to an operator can be effected by dialling, for example,. Fig. Extension line terminations on the multiple field 0 extensions Incoming calls Incoming calls from the public exchange are received by one or more operators, who extend them to the wanted extensions by means of a keyset on their consoles (fig. ).

86 The exchange lines are directly represented on the operators' consoles hy calling lamps and answering buttons. n incoming call is signalled on two operators' consoles simultaneously. The first operator to answer deals with the call. The operators have various facilities for handling calls, of v\hich only some of the more important will be mentioned here. Waiting circuit If the wanted extension is engaged, the operator can place the incoming call on a waiting circuit ("camp-on" position). s soon as the extension becomes free, the call is put through automatically. During the waiting period the operator is recalled every thirty seconds. nnouncement of trunk call On receipt of a long-distance or other urgent call, the operator can enter an engaged circuit to announce the call. warning tone is at the same time extended on the engaged circuit. Parking If the operator is engaged in handling one call when a new call arrives, she can park the original connection while answering the new call. fter extending the latter, she can return to the parked connection. Sequence calls If a calling subscriber wishes to speak to several extensions in succession, the operator can connect the call in sequence. fij. Trunking diagram On the completion of each conversation, the call is then returned to the operator, who extends it to the next extension. Night service When the operators have completed their duties for the day. incoming calls are automatically directed to predetermined night-connected extensions, at which they are answered and from which they are transferred to the desired extensions. 0ext Fig. Connection to register Extra Traffic Facilities RD can. if desired, be equipped for various extra traffic facilities. The more important of these are briefly described below. M C 0 ext. M c 0 ext. Fig. Internal call between extensions in different 0-line groups Group calls ny 0 extensions can be combined into groups of or 0. each group having a "group number". This provides access to any one of a number of persons engaged on similar work, such as card index operators, by dialling the corresponding group number. The call then goes to a free extension within the group. group extension can also be rung on his individual number. utomatic call-back If a calling extension meets the engaged condition, he need not ring again but can be automatically connected as soon as the engaged extension becomes free.

87 0 ext. This is effected by dialling a code digit on receipt of the engaged signal and then replacing the handset. When the called extension becomes free, a callback signal is extended first to the caller. When the latter answers, the called party is rung and connection is established. The extension initiating the call-back procedure is not blocked during the waiting period but can use his telephone for other calls. Direct access Fig. Outgoing call Connection to public exchange Persons in managerial positions may be given the facility of direct access to their subordinates. For this purpose their extension instruments must be equipped with a separate keyset. subordinate can then be rung simply by pressing the appropriate key on the keyset without employing the dial. Paging n audible or visual paging system can be connected to the P..B.X. for paging of up to one hundred persons. Interworking with other private exchanges M 0 0 ext. By dialling a given code digit an extension can connect to another private exchange and obtain access to its extensions. Trunk discrimination If the public system allows subscriber-dialled trunk calls, the P..B.X. can be equipped with a device for supervision of outgoing calls. Extensions may be debarred from dialling trunk calls or allowed to dial trunk calls only on certain routes. Non-restricted extensions are not supervised but can dial trunk calls on any route. Metering Trunk-barred extensions may also make trunk calls, but only with the operator's assistance. If the public exchange transmits metering pulses, such calls can be metered. Fig. X Connection of register on enquiry call Schematic Design Grouping The crossbar switch used in RD has thirty -pole outlets. The outlets are arranged in three "levels"-/!, B and C-with ten outlets on each (fig. ). g G 0 ext. I 0 0 ext. Levels and B are selected through the two actuated positions of the sixth bar, and level C through its neutral position. Thus on actuation of the sixth bar and one selecting bar a particular outlet is selected on level or B. On actuation of a selecting bar alone, a particular outlet is selected on level C. Since the switch has a capacity of 0 outlets, the extensions are grouped in multiples of 0, making three principal groups of 0 extensions each. Connecting circuits SNR, exchange lines FDR-C. etc.. are reached from each 0-line group through two switching stages SL and SLB (fig. ). Fig. 0 Enquiry call x The first stage SL consists of three ten-vertical switches, each containing two multiple fields I and II (fig. ). Each multiple field represents five verticals (V -V and V -V 0). group of 0 extensions is connected to these multiple fields in such a way that every extension line appears on two fields.

88 Fig. Trunking diagram The principle of the twisted multiple is employed (fig. ). This implies that a group of ten extensions shares the verticals in one multiple field with certain 0-line groups but, in the other multiple field in which it is represented, with certain other 0-line groups. This arrangement provides the optimum accessibility. The 0 inlets of the SL stage are wired to the outlets of the SLB stage, so forming the multiple field in this stage. The inlets of the SLB stage are thereafter connected to the various switching units SNR, FDR-C, etc. The switching units may be defined as common and individual units. The common units, comprising register REG and marker M, are used for the setting up of calls and are released as soon as this has been done. The individual units connecting circuits SNR and exchange lines FDR-C, etc. are occupied until the call is completed. Fig. Circuit after transfer of a call The connecting circuits are reserved for internal traffic and are not used on external calls. Every 0-line group has five connecting circuits allotted to it for normal traffic, and access to five common connecting circuits under peak traffic conditions. Enquiry and transfer are effected through special enquiry units FFR. and so do not occupy a connecting circuit (see trunking diagrams, figs. and ). Initiation of call by extension When an extension raises his handset, his line is first identified by the marker. The extension is thereafter connected via a connecting circuit SNR to a free register REG, which returns dial tone. The marker restores (fig. ). 0 ext In order that the registers shall not remain occupied unnecessarily long, they are equipped with automatic time release which enters into operation if more than - seconds elapses before dialling is started. The extension can now dial an internal number or the digit for connection to the public exchange. In both cases the marker is seized once again. If the call is internal, the marker identifies the called extension B and sets up the connection via the already seized connecting circuit SNR. ringing signal is transmitted and. as soon as B answers, the connection is established (fig. ). Fig. Extension of incoming call On an outgoing call the marker selects a free exchange line. The connecting circuit SNR on which the extension was connected to the register is immediately cleared and the extension is connected to the exchange line equipment FDR-C. The loop is closed to the public exchange HC, which returns dial tone to the extension (fig. ).

89 \ To assure that outgoing calls can be made even in the rare case that all connecting circuits are engaged, the switchboard has been equipped with auxiliary connecting circuits (HSNR). The extension is in such case connected via an auxiliary connecting circuit to the register and dials the exchange code. s soon as he obtains a free exchange line, HSNR is restored just like an ordinary connecting circuit. The auxiliary connecting circuits are used exclusively for this purpose and are never accessible for internal calls. If an extension attempts to make an internal call via an auxiliary connecting circuit, busy tone is returned. Enquiry and transfer If during an external call an extension wishes to make an enquiry call, he dials one impulse. The exchange line FDR-C is then switched to a free enquiry unit FFR and is extended thence to a register REG (fig. ). The register returns tone to the extension, who can now dial the internal number. The marker then sets up the call in the same way as an ordinary internal call. The register restores (fig. 0). For transfer of the call, the marker switches the exchange line to the new extension and the enquiry unit is released (fig. ). Incoming call n incoming call from the public exchange is signalled on the operator's console FM. When the operator answers, the exchange line is switched to the operator's equipment FMT and FM via a special switching stage FDK The operator is now in connection with the calling subscriber. She extends the call with the aid of the keyset on her console. The extension number is stored by a register in FMT. The marker then sets up the connection between the subscriber and the wanted extension B in the same way as between two extensions. FMT and FM are restored (fig. ). Fig. Rack unit Mechanical Structure Racks and relay units When installed to full capacity, the P..B.X. consists ot eight rack units (fig. ). The dimensions of all rack units are: height. mm ( ft.), width,0 mm ('"), depth 0 mm (0"). One additional rack unit is required if extra traffic facilities are to be provided. ll racks are supplied factory-wired with plastic-insulated wire. Relays and switches are combined into units which connect to the racks by plug and jack (fig. ). Each unit has an enamelled metal cover as protection against dust and damage. Racks, crossbar switches, relays etc. are made to withstand tropical climates and are in other respects of the same high quality as in L M Ericsson's public systems. Fig. Relay unit with crossbar switch

90 Fig. Operator's console Operator's console The operator's console is modernly designed with casing of pastel-grey polystyrene (fig. ). The buttons are formed as "lamp-buttons", i.e. with lamps built into the buttons, which reduces the size of the console and simplifies the work of the operator. The lamp-buttons are made up in sets (fig. ) which plug into the console. The sets can be easily released for inspection or replacement. The operator's console has space for five counters, which are fitted if the exchange is to have metering facilities. The handset also in grey pastel is characterized by its low weight. It is made for plug-and-jack connection. Signalling equipment Fig. X Lamp-button set for five exchange lines The ringing voltage, V, 0-0 c/s, is supplied from the commercial lighting system via a transformer. In the event of a power failure a standby power unit is automatically switched into circuit to supply the ringing voltage. If desired, a signal generator or transistor unit for c/s can be connected. The tones have a frequency of c/s and come from a transistor unit in the signal equipment. The output voltage can be varied I POM er equipment SV Si V G V fee - c SlV Gv FORC SLV GV FDK-C IT FDR-C uj RD operates on V, which, however, may fluctuate between and V. T The power equipment consists of a storage battery and automatic charger. H l» ^ M.D.F. The capacity of the power equipment depends... on the size of the exchange. The average busy hour r power consumption in a fully installed s> system is normally lallv about. Fig. Exchange room ET Equipment for extra traffic facilities T Work bench B Batteries R Charger Installation and maintenance The exchange is very easy to instal. The rack units are set up in pairs backto-back, the pairs being interconnected by plug-ended cables. The installation thus involves no soldering (figs. and ). It is still further facilitated by the

91 fact that extension and exchange lines connect to the exchange by plug and jack. The exchange needs very little maintenance after its installation. No preventive maintenance whatsoever is required. Maintenance costs can therefore be kept to a minimum. M.D.F. If the installation comprises less than 0 extensions, the M.D.F. may consist of a simple set of terminal blocks mounted on the end of one of the racks. For larger exchanges a more complete M.D.F. is recommended, type BB. with protector strips and test jacks. Technical Data Capacity The maximum capacity is: 0 extensions operators' positions 0 exchange lines registers 0 connecting circuits enquiry units The exchange is made up of detached units which plug into one or more racks. The initial capacity can therefore be easily adapted to the immediate requirements of the organization, and further units added as desired. Usual numbering and codes For a fully installed exchange the numbering scheme is as follows: If only 0 extension lines are installed, two-digit numbers can be used, e.g. 0-. Code for outgoing calls: 0 or enquiry to other extension: / enquiry to operator: or 0 tie lines:,, paging: for paging call, for answer automatic call-back: after busy tone priority call: after busy tone Traffic capacity: The SLV stage is dimensioned for. erlangs per group of 0 extensions (outgoing and incoming), i.e. 0. erlang per extension with /oo congestion. Feed: Individual feed X 00 Q, adjustable to X 0 Q. Power consumption: 0. on an internal call, 0. external. Clearing: The connecting circuits can be strapped for first or last party release. Line resistance: The resistance of an extension line may be up to.000 Q, including the resistance of the telephone set. Dialling: The dial may have any desired numbering and impulse ratio. The dialling speed should normally be - IPS, but the exchange can be adapted to 0 I.P.S. ttenuation: The transmission attenuation on internal and external calls is below. db measured between 00 and,00 c/s. The crosstalk attenuation within the same frequency range is above db.

92 Duration Meter VMF N E R I C S S O N, K T I E B O L G E T E R M I, K R L S K R O N UDC... LME There are many fields of engineering in which plant and apparatus exhibit variations in utilization, speed, output, temperature etc. For the proper operation of such plant it is often essential to have a knowledge of these processes. ERMI has designed a duration meter, type VMF, for simple and quick analysis of the variations in the quantities of interest. By the duration of a load or other quantity is meant the aggregate period during which the quantity is attained or exceeded. If a graph is made of the duration of all quantities, and they are arranged in order of magnitude without regard for their sequence in time, a duration curve is obtained which presents a clear and easily interpreted picture of the magnitude and variation of the quantities during a specific period. This curve can naturally be obtained by other means with a recording instrument of some kind, but in such case the values will be arranged in chronological order instead of in order of magnitude; and if the measurement covers a long period, the task of analysing the curve and converting it into a duration curve is a very laborious one. Fig. X Duration meter VMF ; right with rear door open Terminal block for mains voltage and signal generator is seen inside the door. pplications The duration meter VMF was designed primarily for the use of electricity producers and consumers. The duration curve of the load in an entire utility system, on a single line or of a particular consumer is of very great significance for the solution of many engineering and economic problems

93 \ concerned with the installation and operation of the plant, such as calculations of rates and of line losses. In this case the duration meter is used in conjunction with a kilowatt-hour meter equipped with a contact device which delivers impulses at a frequency proportional to the power. In its present form, however, the meter can be used for many other electrical and mechanical applications such as the measurement of flowing liquids and gases, of various kinds of traffic intensity, and of rotary movements, e. g. the most utilized speeds of motors, etc. The only requirement is that a signal generator which delivers impulses at a frequency proportional to the quantity to be studied can be fitted to the apparatus concerned. Principle s stated, the construction of the duration curve is based on a signal generator which, during a given period, delivers a number of impulses proportional to the quantity to be measured - kwh, cubic feet of gas, or revolutions of a motor - but, as the quantity is related to a given interval of time, the impulses also represent the mean value per unit of time in kw, cu.ft./hr. or r.p.m. The duration meter contains a number of registers so arranged that during a fixed period of time - the recording period - they selectively accumulate the impulses in the order of their delivery from the signal generator. The record on every register, after repeated series of impulses, will therefore represent the number of recording periods during which the register has been in operation. Every impulse consequently corresponds to a given mean value during the recording period; if, for example, four impulses have been delivered during the period, the mean value of the quantity measured during the period will be times the impulse value, and the st th registers will have been actuated. On the first register is read the number of periods during which X the impulse value was attained, on the second register X the impulse value, and so on. The result is reproduced graphically by plotting the sequence numbers or corresponding values of the registers as ordinates and the records or corresponding number of seconds, minutes or hours as abscissa. The resulting points are joined together into a curve which shows the duration over the entire range measured. Under the above circumstances the value would be confined to even multiples of the impulse values, i. e. the test points on the ordinate would be evenly divided along the whole curve. Sometimes, however, one is not interested in the entire curve but only in a small part of it, but in this part a very ac- Effective level ^No. (0 kw) No. II (0 kw) vno. 0 (00 kw) No. (0 kw) ^No. (ISO kw) ^No. (0 It W) No. (0 kw) JVo. ( SO kw) No. (0 kw) No. (0 kw) Fig.» Ja ' Duration curve for an electricity undertaking x No. (0 kw) The measurement covers one month. The power in kw is read along the ordinate and the time in hours along the abscissa. The area within the curve represents the total energy consumption in kwh. gis/er No. I (0 kw)

94 curate analysis is desired. This is provided for in Ermi's duration meter through the fact that the registers can be connected at choice to a large number of test levels - altogether. The test points can thus be adapted entirely to the conditions for each individual apparatus under observation. In fig.. representing the duration curve for an electric load, the registers - the test points - have been concentrated to the upper portion of the curve, which is the part of interest for the utilities' rate calculations. Mechanical Design Duration meter VMF consists of a recording section with twelve registers, a timer for determining the length of the recording period, and a power unit with rectifier for driving the components. The only external terminations required are therefore to 0, or 0 volts a. c. and to a signal generator with contact device fitted with a make contact. The meter is enclosed in a case, the front and rear of which can be opened. Meter data can therefore easily be reset at the site of installation and the components are readily accessible for inspection and service. Recording unit The heart of the recording unit (figs. and ) consists of two rotary 0- step selectors RVF 00 and twelve registers, ordinary telephone subscribers' meters, HS 00. The impulses from the signal generator are fed via relays to one of the 0-step selectors (), which serves as impulse collector; i. e. all impulses from the signal generator - " primary impulses" - enter this selector and, with the aid of the switch {), one can select at choice the number of impulses to be Fig. Duration meter with front door open, 0-step selectors Registers Primary secondar) Timer Relavs Rectifier Mains transformer impulse switch x Terminal block for change of impulse duration

95 0 Fig. X 0 Duration meter with rear door open Terminal block Mains voltage switch Fuses, 0-step selectors Jack strip for connection of registers Primary secondary impulse switch Entry for register leads 0 Connector sockets for checking total number of impulses received and recording periods collected before a "secondary impulse" is sent on. The impulse collector thus serves as range switch since the number of primary impulses is multiplied by the number set on the switch. ny multiplicand between and can be chosen except, and. The secondary impulses from the impulse collector are fed to the second 0-step selector () - the level distributor - which distributes the impulses to the desired level. There are levels, represented in the meter by a strip of jacks (), into which the twelve registers () can be plugged in any desired combination. The jack strip contains also two jacks (0) for recording the total number of primary impulses received and the number of recording periods. Two registers may thus be allocated for this purpose if desired. Signal generators with different impulsing characteristics can be connected to the duration meter. The impulse duration, however, should not be less than second. Timer The timer (//) is of standard Ermi type. It consists of a self-starting synchronous motor which, via gearing, actuates a contact springset with make function. The closure time is seconds. By change of gearwheels the duration of the recording period can be adjusted to, 0, 0, 0 or 0 minutes. Power unit ll components - 0-step selectors, registers etc. - are designed for volts d. c. But for greater convenience in use, the instrument has been equipped for direct mains connection through a power unit consisting of a transformer (), rectifier () and voltage switch (). The transformer is protected by two fuses (). The voltage switch provides tappings for 0, or 0 V mains.

96 Technical Data Tappings: 0, and 0 V, 0 c/s. Permissible voltage variation: ± 0 %. Permissible temperature variation: - 0 to + 0 C. Power consumption: approx. m at 0 V, 0 c/s, momentary values of about 0 m. Load on impulse contact of signal generator: m at V d. c. Number of test levels: + for checking total number of recording periods and total number of primary impulses. Number of registers: with -digit drums. Separate set of 0 registers for recessed mounting can also be provided. Recording period: standard mins.:, 0, 0, 0 or 0-min. periods can be arranged if desired. Max. number of primary impulses per recording period.. Restoring time Weight Dimensions less than sec. about. kg (0 lb). 0 X 0 X 0 mm (Va X V X V«in.).

97 \ NEWS/rom ll Quarters of the World Large Orders for L M Ericsson New Danish Contract for 0 million Kronor L M Ericsson and the Copenhagen Telephone Company have signed a contract for continued deliveries of crossbar equipment for extension of the Danish automatic network. The contract covers the delivery and installation of automatic exchange equipment for 00,000 subscribers, as well as automatic trunk equipment. The Copenhagen Telephone Company is the largest of the three private telephone operating companies in Denmark, its area comprising Zealand with Copenhagen, the islands of Lolland-Falster and Bornholm, with altogether some 00,000 subscribers. large part of the equipment for the Danish market is manufactured by Ericsson's Danish associates, Telefonfabrik utomatic /S, of Copenhagen, who in the past year have greatly expanded their production resources for crossbar equipment. Cable and power plant for the telephone exchanges are also being supplied by Danish factories. The new contract covers equipment for at least 0 million Kronor. key to operate on the Ericsson crossbar system, and,000 telephone instruments. fter the installation of this equipment L M Ericsson will have supplied to Turkey automatic exchanges covering,00 lines at towns throughout the country. Lebanese Telephone Network to be Extended to 00,000 Lines In hard competition with French, Italian, Japanese and German telephone manufacturers, L M Ericsson has been awarded a contract by the Lebanese P.T.T. for automatic exchange equipment and telephone instruments to a value of some 0 million Kronor. The installation of this equipment will bring the Lebanese automatic network up to nearly 00,000 lines, all of which have been supplied by L M Ericsson. New Telephone Factory in ustralia new telephone factory is to be built at Broadmeadows near Melbourne by L M Ericsson's ustralian subsidiary, L M Ericsson-Trimax Pty. Ltd. The first stage is to comprise about 0,000 sq. ft. of factory and office accommodation to permit expansion of the production of telephone exchange and other telecommunication material. Substantial orders for modern crossbar switching equipment for automatic exchanges of the ustralian Post Office will be met by the new factory, which is expected to be in operation by the end of next year. Canada to Install Exchanges for Intercontinental Calls L M Ericsson has received an order from Canadian Overseas Telecommunication Corp. for two automatic exchanges for intercontinental calls. They are to be installed at Montreal and Vancouver and will link the national Canadian network with the tlantic and Pacific cables of the British Commonwealth roundthe-world project. The exchanges will connect calls between Canada, Europe and ustralia, and will be of Ericsson crossbar type. The value of this first order is only about million Kr., but the installation carries with it a considerable prestige value. (Below) The new office building of L M Ericsson Ltd. in Montreal. 0,000 Subscriber Lines for Turkey L M Ericsson has signed a new contract with the Turkish P.T.T. for the delivery of telephone equipment, the main item being the addition of 0,000 subscriber lines at automatic exchanges already supplied by L M Ericsson. The contract also includes a new 000-line exchange, which will be the first public exchange in Tur-

98 Holger Ohlin The announcement of Holger Ohlin's death on Friday the th of ugust did not come entirely unexpectedly to those who had followed his stubborn struggle against illness during his closing months. The will to win was strong in him to the last. Holger Ohlin's lifework was devoted almost entirely to L M Ericsson. He entered the company's service as Head of the Treasury Department in. and in was appointed Vice President and Head of Central Sales. During the troublesome period for the company that followed on the Kreuger crash, great demands were placed on his knowledge and experience; and then, as in the difficult work of reconstruction in the subsequent years, his abilities and intelligence were a great asset to the company. In conjunction with the reorganization of the management in 0 he was appointed Chief Financial Officer, being the first holder of this appointment. From to he held the powers and responsibilities also of Executive Vice President. Holger Ohlin held degrees in economics and law, a combination which proved to be of great value to him. He also had a wide knowledge of languages, which meant that he could devote considerable attention to the foreign problems of the company, both those of an economic and financial nature and those concerned purely with business management. He devoted special interest to the Italian section of the Group, where the problems have been many and difficult. His efforts were acknowledged in the award of the Order of Knight Commander of Merito Italiano, a distinction on which he rightly placed great value. Despite the heavy load of work involved in his Ericsson appointments he was also member of a number of boards within the Group he found time for various public assignments, in the conduct of which his sagacity and sound knowledge were highly appreciated. When Holger Ohlin retired on pension last year at the age of. we in the management of the company hoped that we might continue to draw on his fund of experience for a long time to come. He himself looked forward to a period which would give him the freedom to devote his time to many in Memoriam questions outside his previous sphere of work. But fate decreed otherwise. Holger Ohlin, the able, versatile and always helpful administrator, the confident, cheerful and kindly Scanian, is no more. mong those who mourn his departure are the many thousands of Ericsson employees who join with me in a word of warm gratitude to our friend for what he has meant to us all. Sven Ture berg 0 British Railway Signal Engineers Visit L M Ericsson The Institution of Railway Signal Engineers (IRSE) celebrated its halfcentenary in. The annual visit paid by the Institution to railway signalling plants and manufacturers inside or outside the British Isles was this year made to Sweden, where the State Railways and L M Ericsson had the pleasure of cooperating in the arrangements for the IRSE Golden Jubilee Convention. The party arrived in Stockholm on May and immediately proceeded to the Midsommarkransen offices of L M Ericsson, where they were welcomed by the president, Sven T. berg. The group was able to study L M Ericsson's products in the Exhibition Room and to make a quick tour of the factory. In the days that followed. IRSE visited the Stockholm Central Station, where the State Railways demonstrated the relay interlocking plant at present under construction there, for which L M Ericsson had arranged a model of the track diagram to be used in the new plant. The State Railways had also arranged a display of the signalling equipment they employ principally of Ericsson make. IRSE thereafter visited the nge C.T.C. plant, the largest in Europe, also delivered by L M Ericsson. Ericsson C.T.C. for Spanish Railways Cia Espafiola Ericsson and L M Ericsson have received orders from the Spanish Railways, RENFE, for C.T.C. equipment on the Valcncia- Sagunto line, the southernmost section of the Valencia-Barcelona line. Cia Espafiola Ericsson is to supply relay interlockings for the seven remote-controlled stations, and blocks between them, and L M Ericsson is to supply the remote control equipments. Five of the seven stations have two main tracks and the other two stations three main tracks. The line is single track, 0 miles in length, and normally carries 0 trains a day. The C.T.C. system will he of standard Ericsson type with keyboard operation and a semicircular, sectional track diagram carrying indication lamps only. The plant is to be in operation by. Spain will be the eleventh country to which L M Ericsson has supplied C.T.C. equipment.,0 Kronor in nnual LME Grants The Telefonaktiebolaget L M Ericsson Foundation for the Promotion of Electrotechnical Research has made grants amounting to,000 Kronor from the year's funds to eight persons. The company's Foundation for Travel and Other Educational Grants has awarded,0 Kronor to employees of the Ericsson Group and to employees of the Swedish Telecommunications dministration.

99 \ President Tubman at L M Ericsson Liberia's President, William Tubman, paid an official visit to Sweden at the end of September, in the course of which he made a call at L M Ericsson's Midsommarkransen factory. The President, accompanied by the Prime Minister, Tage Erlander, Cabinet Minister, Sven af Geijerstam, and a large following, was welcomed by the Chairman of the Board, Dr Marcus Wallenberg. fter a brief account of the company's activities by President Sven T. berg, the party was shown round the Exhibition Room. Mr. berg presented the President with a set of Ericofons in the Liberian colours, red, white and blue, and an Ericovox. L M Ericsson's first large order from the Liberian government had been obtained in September %. It comprised local automatic exchanges and outside plant for Monrovia and other towns to a value of nearly million kronor. further contract was recently concluded with Liberia for the supply of carrier equipment for the national trunk network. President William Tubman with (right) Dr Marcus Wallenberg and Mr. Sven T. berg and (left) Mr. B. Thisell. The inauguration at Katmandu, capital of Nepal, of the,000-line automatic exchange of Ericsson type RF 0. King Mahendra Bir Birkram Shah Deva cuts the tape across the entrance to the Katmandu Telephone Exchange. On the left is Dhundi Raj, Secretary of the Minister of Communications, and on the right Chief Engineer Heramba Prasad I'padhyaya. (bove) From left: Director General bdul Jabbar Ismail, Mr. Usama, and General M.. Baghdadi from the Iraq P.T.T. on a visit to Midsommarkransen.

100 Ericsson Maintenance Conference Crossbar Comes to Malaya Ericsson crossbar systems have begun to meet with an increasing demand in Southeast sia. Public crossbar exchanges are already operating in Burma, Thailand and Indonesia, and new exchanges are being installed. In March L M Ericsson was invited by Malayan Telecoms to run an introduction course in crossbar technique for exchange and installation supervisors from the whole of the Malayan Federation. Concurrently with this course, an information conference on the crossbar system was arranged which was attended by the Central Operations Management of Malaya Telecoms. The course and the conference, both of which were held at the training centre of Malaya Telecoms at Kuala Lumpur, met with an enthusiastic reception, and the knowledge imparted will undoubtedly be of value to the participators. For the first crossbar P..B.X.'s are soon to be installed in Malaya a country whose telephone density is above the average for sia and is growing strongly. (bove) Some of the participators during a break in the information conference. (From left) Ericsson engineers. Uvhagen, K. lbertsson and H.S. ndersson; L. Bywater, Lee Chye Watt, G.. Langley, of Telecoms; and F. Loh of Singapore Telephone Board. t this year's maintenance conference, which was held in Stockholm from June to June, most of the Latin merican telephone administrations, as well as the Swedish, were represented. s in the preceding year, the conference dealt with "integrated maintenance", comprising the ways and means of rational supervision and control of the functioning of telecommunications plant. The term "integrated maintenance" is here taken as meaning that the same principles are applied in the maintenance of exchange equipments, long distance and local cable networks. Since. at maintenance conferences and elsewhere, L M Ericsson has advocated a radical reexamination of the maintenance principles as earlier practised. The form of maintenance recommended by L M Ericsson for automatic exchanges is called "controlled corrective maintenance". These recommendations were discussed at this year's conference, as also different aspects affecting the choice of policy in the maintenance of telecommunication plant. special exhibition, "Maintenance ", had been arranged for the conference, at which were shown the equipments considered necessary for rational maintenance of Ericsson automatic exchanges (see photo below left). The conference devoted special interest to the equipments for mechanization of maintenance supervision, and the new methods of maintenance organization which the equipments require were extensively discussed. fter the conference a round trip was arranged to the local telephone administrations in Gothenburg, arhus, Odense and Copenhagen. Some of the Danish P.T.T. plants for long distance telephony were also visited in Copenhagen. The Swedish and Danish administrations gave a full account of their experience of the operation of subscriber-controlled networks. Sixteen administrations and operating companies had sent delegates to the year's conference. Representatives of the Swedish ir Force were also present as observers. The discussions took place in Spanish and English with simultaneous interpretation between the two languages.

101 UDC.. LME WIDL, W: n Experimental Data Transmission System. Ericsson Rev. ():, pp.. During the last few years technical development has entailed an everincreasing demand for the transmission of vast amounts of data between geographically separated centres. Particularly military defence systems are in urgent need of data transmission equipment permitting higher speeds. It is therefore natural that the system described in this article should have been developed to the order of Kungliga Flygforvaltningen (the Royal Swedish ir Force dministration), which also drew up the required basic specification. This resulted in the construction of a phase-shift data transmission system permitting the transmission of binary digits at a speed of up to 00 bauds over telephone circuits. In the article a description is given of the function and construction of the system. In conclusion a few test results are given. EILERTSEN. & KILNDER, S: Crossbar P..B.X. Rev. ():, pp.. UDC.. LME RD. Ericsson The excellent performance of the crossbar switch is being increasingly utilized for private automatic exchanges. In the last few years L M Ericsson has brought out several types of crossbar private exchanges. One of them is the P..B.X. RD presented in this article. UDC... LME ERICSSON, N: Duration Meter VMF. Ericsson Rev. ():, pp. 0. There are many fields of engineering in which plant and apparatus exhibit variations in utilization, speed, output, temperature etc. For the proper operation of such plant it is often essential to have a knowledge of these processes. ERMI has designed a duration meter, type VMF, for simple and quick analysis of the variations in the quantities of interest.

102 e Ericsson Group ssociated and co-operating enterprises * EUROPE Denmark L M Ericsson /S Kebenhavn F, Finsensvej, tel: Fa, tgm: ericsson Telefon Fabrik utomatic /S Kobenhavn K, maliegade, tel: C, tgm: automatic Dansk Signal Industri /S Kebenhavn F, Finsensvej, tel: Fa, tgm: signaler Finland O/Y L M Ericsson /B Helsinki, Fabianinkatu, tel:, tgm: ericssons France Soci^te des T lphones Ericsson Co/ombes (Seine), Boulevard de la Finlande, tel :CHrlebourg -00, tgm: ericsson Paris e, Rue de Courcelles, tel: CRnot -0, tgrn: eric teliers Vaucanson, Paris XX, B P..0,tel: MENilmontant -0 tgm: atelcanson Great Britain Swedish Ericsson Company Ltd. London, W. C., High Holborn, tel: Holborn 0, tgm: tel eric Production Control (Ericsson) Ltd. London, W. C., High Holborn, tel: Holborn 0, tgm: productrol holb Italy SETEMER, Soc. per z. Roma. Via G. Paisiello, tel:.,., tgm: setemer SIELTE, Soc. per z. Roma, C. P. 0 ppio, tel: 0, tgm: sielte FTME, Soc. per z. Roma, C.P. 0 ppio, tel: 00. tgm: fat me gencies - EUROPE Belgium Electricite et Mecanique Su^doises Bruxelles, Rue de Stassart, tel:, tgm: electrosuede Greece "ETEP" S.. Commercials & Technique thens, Lycavettus Street, tel: 0, tgm: aster-qthinai Iceland Johan Ronning H/F Reykjavik, P. O. B., tel: 0, tgm: ronning Ireland Communication Systems Ltd. Dublin, Pembroke Road, Ballsbridge, tel: 0 tgm: crossbar Yugoslavia Merkanlile Inozemna Zastupstva Zagreb, Pot pretinac, tel:, tgm: merkantile, telex: 0- SI Burma Burma siatic Co. Ltd. Ericsson DepartmentRangoon, P.O.B. 00, tel: 0, tgm: ericsson Cambodia The East siatic Company Ltd. Phnom-penh, P.O.B., tel: -00-0, tgm: pyramide Ceylon Vulcan Trading Co. (Private) Ltd. Colombo, New Caffoor Building, 0. Church Street, tel: -, tgm: vultra China The Ekman Foreign gencies Ltd. Shanghai, P. O. B., tel: -, tgm: ekmans Netherlands Ericsson Telefoon-Maatschappij, N.V. Rijien (N.Br.), tel: 0-, tgm: erictel den Haag Scheveningen, 0, Palacestraat, tel: 00, tgm: erictel-haag Norway /S Elektrisk Bureau Oslo NV, P.B. 0, tel: Centralbord 0. tgm: elektriken /S Industrikontroll Oslo, Teatergaten,tel: Centralbord 0, tgm: indtroll /S Norsk Kabelfabrik Drammen, P. B. 0, lei:, tgm: kabel /S Norsk Signalindustri Oslo, P. B. Mj, tel: Centralbord, tgm: signalindustri Portugal Sociedade Ericsson de Portugal, Lda. Lisboa,, Rua Filipe Folque, tel:, tgm: ericsson Spain Cia Espanola Ericsson, S.. Madrid,Torre de Madrid er piso, oficina, Plaza de Espana, tel : 00, tgm : ericsson Sweden Telefonaktiebolaget L M Ericsson Stockholm, tel: 00 00, tgm: telefonbolaget B lpha Sundbyberg, tel:00, tgm: aktiealpha-stockholm B Ermex Soma, tel: 000, tgm: elock-stockholm BErmi.Kar/sfcrona, tel: 00, tgm: ermibolag-karlskrona B Rifa Bromma, tel: 0, tgm: elrifa-stockholm B Svenska Elektronror Stockholm 0, tel: 0 0, tgm: electronics Cyprus Zeno D. Pierides Larnaca, P.O.B., tel: 0, tgm: pierides Hong Kong The Swedish Trading Co. Ltd. Hongkong, P. O. B. 0, tel: -, tgm: swedetrade Iran Irano Swedish Company B, Teheran, Khiabane Sevom Esfand, tel:, tgm: iranoswede Iraq Usam Sharif Company W.L.L. Baghdad, Sinak-Rashid Street, tel: 0, tgm: alhamra Japan Gadelius & Co. Ltd. Tokyo C, P. O. B., tel: 0-, tgm: goticus Korea Gadelius & Co. Ltd. Seoul, I. P. O. Box,tel:, tgm: gadeliusco Kuwait Latiff Supplies Ltd. Kuwait, P. O. B., tel: 0, tgm: latisup Lebanon Swedish Levant Trading (EMe B. H lou) Beyrouth, P. O. B., tel:, tgm: skefko Pakistan Vulcan Industries Ltd. Karachi City, P. O. B., tel: 0, tgm: vulcan Philippines U.S. Industries Philippines Inc. Manila P. R., P. O. B., tel: --, tgm: usiphil Saudi rabia Mohamed Fazil bdulla rab Jeddah, P. O. B., tel: 0, tgm: arab Singapore and Malaya The Swedish Trading Co. Ltd. Singapore, Chartered Bank Chambers, Battery Road, tel:, tgm: swedetrade L M Ericssons Driftkontrollaktiebolag Solna, tel:, tgm: powers-stockholm L M Ericssons Signalaktiebolag Stockholm Sv, tel: 0 00, tgm: signaibolaget L M Ericssons Svenska Forsdljningsaktiebolag Stockholm, Box, tel: 00, tgm: ellem Mexikanska Telefonaktiebolaget Ericsson Stockholm, tel:0000, tgm: mexikan Sieverts Kabelverk B Sundbyberg, tel: 0, tgm: sievertsfabrik-stockholm Svenska Radioaktiebolaget Stockholm, lstromergatan, tel: 0, tgm: svenskradio B Ostmarks Ldsfabrik Eskilstuna, Munktellsgatan, tel: Switzerland Ericsson Telephone Sales Corp. B, Stockholm, Zweigniederlassung Zurich Zurich, Postfach Zurich, tel:, tgm: telericsson West Germany Ericsson Verkaufsgesellschaft m. b. H. Diisse/dorf, Postfach, tel:, tgm: erictel. SI India Ericsson Telephone Sales Corporation B New Delhi, P.O.B., reg.mail: / saf li Road (Delhi Estate Building), tel:, tgm: inderic Calcutta, P. O. B., tel: -, tgm: inderic Indonesia Ericsson Telephone Sales Corporation B Bandung, Djalan Dago, tel:, tgm: javeric Djakarta, Djalan Gunung Sahari, tel: Kota, tgm: javeric Lebanon Telefonaktiebolaget L M Ericsson, Technical Office Beyrouth, Rue du Parlement, Immeubte Bisharat, tel:, tgm: ellem Turkey Ericsson Turk Ticaret Ltd. $irketi nkara. dil Han, Zafer Meydani, Yenisehir, tel: 0, tgm: ellem Syria Georgiades, Moussa & Cie Damas, Rue Ghassan, Harika, tei: -0-, tgm: georgiades Thailand Ericsson gency Office, Telephone Organization of Thailand Bangkok, Ploenchitr, tgm: telthai. FRIC Road, tel: Ethiopia Swedish Ethiopian Company ddis baba, P. O. B., tel:, tgm: etiocomp Ghana The Standard Electric Company ccra, P.O.B., tel:, tgm: standard Kenya, Tanganyika, Uganda, Zanzibar Transcandia Ltd. Nairobi, Kenya, P.O. B., tel:, tgm: transcanda Liberia Swedish gencies Liberia Co. Monrovia, P.O.B. 0, tel:, tgm: salco (Except sales to public institutions) Libya The Gulf Trading Co. Tripoli, P.O.B., tel:, tgm: gultraco Mauritius Mauritius Trading Co. Ltd. Port Louis, P.O.B. 0, tgm:agentou Morocco Elmar S.. SEYRE Tangier, Francisco Vitoria,, tel: -0, tgm: elmar Istanbul, Han, Kat tel:.,. FRIC Egypt (UR) Telefonaktiebolaget LM Ericsson, Egypt Branch Cairo, P. O. B., tel:, 0, tgm: elleme Northern and Southern Rhodesia, Nyasaland LM EricssonTelephoneCo. (Pty.) Ltd. (Branch Office of LM Ericsson Telephone Co. Pty. Ltd. in Johannesburg) Salisbury, Southern Rhodesia, P.O.B., tel: 0 0. tgm: ericsson South frica, South-West frica L M Ericsson Telephone Co. Pty. Ltd. Johannesburg, Transvaal, P. O. B. 0, tel: -, tgm: ericofon Tunisia Telefonaktiebolaget LM Ericsson, Technical Office Tunis, Boite Postal e 0, tel: 00,tgm:ericsson MERIC rgentine Cla Ericsson S.. C. I. Buenos ires, Casilla de correo 0,tel: 0, tgm: ericsson Cia rgentina de Tel^fonos S.. Buenos ires, Peru, tel: 0 0, tgm: catel Cfa Entrerriana de Telefonos S.. Buenos ires, Peru, tel: 0 0, tgm: catel Industrias Electricas de Quilmei S.. Quilmes FCNGR, de Octubre 00, tel: 0-, tgm: indelqui-buenosaires Brazil Ericsson do Brasil Come>cio e Industria S.. Rio de Janeiro, C. P. 0, tel: -00, tgm: ericsson Canada LM Ericsson Ltd. Montreal, P.Q., 00 Laurentian Boulevard, City of St. Laurent, tel: 0, tgm: caneric Toronto, Ont., P. O. B., tel: BE -0 Mozambique J. Martins Marques Lourenco Marques, P. O. B., tel:, tgm: tinsmarques Nigeria I.P.T.C. (West frica) Ltd. Lagos, P.O.B. 0, tel:, tgm: consult Sudan Vietnam TECOM Technical Consulting Vo Tuyen Dien-Thoai Viet-Nam, and Machinery Co. Ltd. Khartoum, P.O.B., tel:, ext. Saigon, Dai-lo Thong-Nhut, tel: 00, tgm: telerad, tgm: sutecoma MERIC Bolivia Johansson & Cla, S.. La Paz, Casilla, tel: 00, tgm: Johansson Costa Rica Tropical Commission Co. Ltd. San Josi, partado, tel:, tgm: troco Curacao N. W, I. S. E. L. Maduro & Sons, Inc. Curocao, P. O. B., tel: 00, tgm: madurosons-willemstad Dominican Republic Garcia & Gautier, C. por. Son/o Domingo, partado, tel:, tgm: gartier Guatemala Nils Pira Ciudad de Guatemala, partado, tel:, tgm; nilspira-guaternala Honduras Quinchn Leon y Cla Tegucigalpa, partado, tel:, tgm: quin~" Jamaica Morris E., tel, tgm: encsson-santiage. dechile Colombia Cla Ericsson Ltda. Bogotd, partado ereo 0, tel: --00 tgm: ericsson Ecuador Teleionos Ericsson C.. Quits Casilla, tel: 00, tgm: ericsson Guayaquil, Casilla, tel; tgm: ericsson Mexico Telefonos Ericsson S.. Mexico D.F., partado, tel: 0, tgm: coeric Industria de Telecomunicacin S.. de C.V. Mexico, D.F. Lond-! res No., tel: 00, tgm: in- dustel Peru Cla Ericsson S.. Lima, partado, tel:, tgm: ericsjon! Soc. Telefnica del Peru, S.. I requipa, partado, tel: 00, tgm: telefonica Uruguay Cla Ericsson S.. Montevideo, Casilla de Correo, tel: -., tgm : ericsson US The Ericsson Corporation New I York, N. v 00 Park venue, } tel: Murray Hill -00. gm: erictel North Electric Co. Ga/ion, Ohio, P. O. B., tel: Howard -0, tgm: northphone-galionohio Venezuela Cla nnima Ericsson Caracat, partado, tel:, tgm: ericsson Telefonos Ericsson C.. Corocos, partado, tel:, tgm: tevela USTRLI & OCENI ustralia L M Ericsson Telephone Co. Pty. Ltd. Melbourne C {Victoria), 0 Collins Street, tel:, tgm: ericmel L M Ericsson Trimax Pty. Ltd. Coburg N (Victoria), P.O.B., tel: 0, tgm: trimax Nicaragua Edmundo Tefel Managua, D.N., partado Postal, tel: 0, tgm: edfalco Panama Productos Mundiales, S., Panama, R. P., P. O. B., tel: -0, tgm: mundi Paraguay S.. Comercial e Industrial H. Petersen suncidn, Casilla, tel:, tgm: pargtrade Puerto Rico Splendid Inc. San Juan, P. O. B., tel: -0, tgm: splendid El Salvador Dada-Dada & Co. San Salvador, parlado, tel: 0, tgm: dada Surinam C. Kersten & Co. N. V. Paramaribo, P. O. B. 0, tel:, tgm: kersten Trinidad, W. I. Leon J che - Ltd. Port-of-Spain, 00 Frederick Street, tel:, tgm: achegram US Clark Walter Corporation Ntwark, N. J., Broad Street, tel: Mitchell -, tgm: wirewalter-newarknj. (For intercom) Slate Labs. Inc. New York, N. Y., Park venue South, tel: Oregon -00, tgm: statelabs (For electron tubes) USTRLI & OCENI.

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105 ERICSSON REVIEW Vol. XXXIX No. RESPONSIBLE PUBLISHER: HUGO LINDBERG EDITOR: SIGVRD EKLUND, DHS EDITOR'S OFFICE: STOCKHOLM SUBSCRIPTIONS: ONE YER $.0; ONE COPY $ 0.0 CONTENTS The Development and Future of Wide Band Carrier Systems Planning of Multi-Exchange Networks with id of a Computer III Practical pplication of Planning of Multi-Exchange Networks with id of a Computer. Exchange Locations and Boundaries The Dry Reed Switch a Sealed Contact of Great Reliability LM Ericsson News from ll Quarters of the World On cover: Demonstration Panel Crossbar System RF one of Ericsson's most Useful ids in page for LM the Training in Telephone Exchange Technique. COPYRIGHT TELEFONKTIEBOLGET LM ERICSSON PRINTED IN SWEDEN, ESSELTE B, STOCKHOLM

106 The Development and Future of Wide Band Carrier Systems ERIK J ERIKSEN, TELEFONKTIEBOLGET LM ERICSSON, STOCKHOLM UDC.. LME The use of wide band carrier systems on different transmission media such as symmetrical pair cables, open-wire lines, coaxial cables and waveguides is dealt with in this article with special reference to circuit capacity and future development. The article, whose emphasis is on the coaxial cable h.f. line, is based on an address given before the Swedish ssociation of Electrical Engineers, held on March.. The modern long distance network has many different transmission systems. These systems use open-wire lines, symmetrical pair cables, coaxial cables or radio links as transmission media. For longer transmission distances, instead of sending several individual telephone circuits it is more economic to multiplex these so that few but in general wider frequency bands are sent. It will be seen in fig. how the cost per circuit kilometre varies as a function of the number of circuits. It is seen that a given system is cheaper, when calculated on the basis of the cost per circuit, if there are more systems operating in parallel, due to there always being certain parts of the equipment which the systems can use together. However, fig. also shows that the multicircuit systems per circuit-kilometre are cheaper than those having fewer circuits. It is apparent that the annual charges per unit length are many times greater for a physical circuit than for a circuit in a coaxial system. It is natural that it must be so. The following figures illustrate this: for a physical circuit of an open-wire line using mm dia. conductor, about 00 kg of copper are used per km, whereas only 0. kg of copper is used per km per circuit in a.00-circuit system. Even if the terminal equipment is included, the picture is not changed very much. The cost per circuit of the terminal equipment is mainly independent of the number of circuits, at any rate for systems having a large number of circuits. Relative cost per circuit km (excluding terminal equipment) Fig. X Comparative annual costs per circuit-kilometre as a function of the number of circuits (Reproduced from Bell Laboratories Record. February 0) Open-wire Systems. Voice frequency circuits. Voice frequency circuits and C carrier (-circuit system ). Voice frequency circuits and C and J carrier ( and -circuit system ). O carrier system (-circuit system) Carrier Systems for Radio Links TD- (00-circuits per baseband) TH (00 circuits per baseband) Symmetrical Pair Cable Systems Voice frequency circuits. -wire Voice frequency circuits, -wire K Carrier (-circuit system, 0 kc/s) 0 N Carrier (-circuit system. 0 kc/s) ON Carrier (-circuit system) Carrier Systems for Coaxial Cables LI (00-circuits tube pair) L (0-circuits tube pair) 0 VOtCE ^SEQUENC* Q VOICE FCIEQ. i c cfimer VOXE =G 0 t C U CSniER Q o c*»«tso MICROWVE RELY 0 roo. VOICE FREQ - WIRE G VO-CE «eo -z wine O * CRRIER - SMLL. C*Lt ( ) N CRRIER 0 ON CRRIER COXIL. CBLE V DOO N toooo Number of circuits 0

107 \ till, km fter what has been said above it will be understood that there is a great economic urge toward systems with ever-increasing bandwidth. Two important factors determine the limits in the number of circuits which a system will have.. There must be a traffic demand which is sufficient to fill the systems so that they are effectively exploited. There must be a technique which is in problems posed by wideband systems. position to solve the technical To obtain an answer to the problem concerning the traffic demand, let us study how the Swedish Telecommunications Network has developed during the past years. In fig. it will be seen that the number of circuit-kilometres has approximately trebled every tenth year. Sixty-five percent of these circuitkilometres are on carrier circuits. The different groups of circuits increase in size at the same time as the network grows as regards the number of carrier circuit-kilometres. bout 0, carrier systems for 0 circuits were economic in Sweden and about 0,,00-circuit systems were introduced, this too being a trebling in ten years. If the technical development can keep pace, we should therefore have a traffic demand for.000-circuit systems in Sweden in 0. It is therefore justifiable to study the technical aspects in this development which have so far occurred and to see what limits are placed on the maximum number of circuits by the different transmission systems. Open-wire Line and Symmetrical Pair Cable Systems Fig. X Development of the Swedish Telecommunications Network during the past 0 years. Length of telecommunications circuits. (From Swedish Official Statistics 0) Local lines Trunk circuits - - Rural circuits Telegraph circuits Carrier technique was first used on open-wire line routes. The open-wire lines had about a tenth of the attenuation per unit length of that of the symmetrical pair cables and in addition were not limited in frequency by loading coils. In the beginning, an attempt was made with + circuits and soon afterwards, a -circuit system was placed above this -circuit system. The highest frequency sent was thereby about 0 kc/s. It is not practicable to use frequency division multiplex systems appreciably over this frequency on open-wire lines. The development of systems for cables with symmetrical pairs was similar. Initially, a -circuit system was used (in certain cases even -circuit systems) the loading being lightened so that there was a sufficiently large bandwidth available. development toward systems having greater bandwidths necessitated greater cable attenuation being compensated with the help of amplifiers. Only when the principle of negative feedback was discovered was it possible to obtain sufficient stability of gain for an increased compensation of attenuation. It was now possible to remove the loading coils completely and then a rapid development began, resulting in -circuit, -circuit and 0-circuit systems being designed in a 0 year development period (0-0). fter that, the development toward even wider band systems also stopped. Why did such a promising development come to an end? s far as open-wire systems and symmetrical pair cable systems are concerned, it is the crosstalk which it is not possible to master. For 0-circuit systems which go up to kc/s in the frequency band, it is sufficient for a capacitive unbalance of pf to reduce the crosstalk attenuation to about 0 db. It will be understood that despite rejointing, use of balancing equipment etc., the problem of crosstalk is critical. In spite of the fact that recently it has been possible to transmit 0-circuit systems on special plastic insulated symmetrical pair cables, unscreened pairs are not suitable for transmission which is free from crosstalk at the upper frequencies.

108 Coaxial Cable Systems History coaxial tube is made up of an inner conductor surrounded by a cylindrical outer conductor. Due to this construction the electromagnetic field is limited in an outward direction and crosstalk between several tubes within the same cable is to all intents and purposes eliminated. Contrary to the case with the symmetrical pair cables where the crosstalk increased with frequency, it is found that for the coaxial cable the crosstalk decreases with increase in frequency. Typical values for the coaxial cable standardized by CCITT for a km length at 0 kc/s are as follows: Near-end crosstalk.0 N Far-end crosstalk 0. N lready at 00 kc/s, the crosstalk contribution is at the limit of that which can be measured. These good crosstalk characteristics mean that traffic in the two directions (/)->B and B^) can be carried in the same cable. The cable attenuation, which of course is another very important factor in the judgement of transmission characteristics, increases smoothly, practically as the square root of the frequency for this type of cable. It must be said that the coaxial cable is an extremely good medium for transmission of wideband signals compared with symmetrical pair cables and open-wire lines. If it is required to transmit many circuits over a coaxial tube, one has to use high frequencies. The high cable attenuation at these frequencies leads, of course, to there being short distances between the line repeaters. The development has so far been the following:. The LI-system was put into operation in the beginning of the 0's in US, initially with 0 circuits and later with 00 circuits per pair of tubes. Repeater spacing miles. Highest frequency sent. Mc/s.. The first coaxial system in the world with 0 circuits per pair of tubes was inaugurated in Sweden in. Repeater spacing. km. Highest frequency sent. Mc/s. The system is that standardized by CCITT.. The L system was put into operation in (US). Number of circuits per pair of tubes,0 Repeater spacing miles. Highest frequency sent. Mc/s.. In the first Mc/s system was put into operation in Sweden, this too being the first of its type in the world. Number of circuits per pair of tubes,00 Repeater spacing. km This system is also standardized by CCITT It will be seen that there has been a trebling of the circuit capacity by halving the repeater spacing as regards the merican systems and the systems standardized by the CCITT. Technique ll systems are otherwise mainly designed using the same principle. It is due to an ever-advancing technique that success has been achieved in increasing the bandwidth and thereby the circuit capacity. The most important characteristics of the coaxial line amplifier equipment will here be described in brief. Where numerical values are mentioned, they refer to a Mc/s system. The cable attenuation at the highest frequency is. N per amplifier section. For a route, e.g. Stockholm-Gothenburg, the cable attenuation is altogether 00 N (without amplification only /0 :! " of the original power would reach its destination). This total attenuation has to be compensated so exactly that the residual error is only about 0. N.

109 It will be understood that the gain of each amplifier must correspond very accurately with the cable attenuation and what is equally important that the gain must be very stable with time. The necessary stability is obtained by using heavy negative feedback. On top of all this, the cable attenuation is not stable with temperature but varies /oo per degree Celsius. With the temperature variations that occur here in Sweden at about a depth of 0 cm below the surface, the influence of temperature variations corresponds to about ± 0. N per section at the highest frequency sent. Such an attenuation contribution which varies with time must be compensated by some form of automatic level regulation device. In this case a line pilot which is injected into the frequency interstice between the telephone bands is used. The pilot frequency is extracted by filters at the repeater stations and the pilot level is compared with a standard level. The temperature compensating network is regulated until there is agreement between the levels of the pilot and the standard. It is quite clear that the majority of all these repeater stations must be unattended, due to their large number. There must therefore be auxiliary equipment at the unattended stations for automatic fault indication. The coaxial amplifiers are supplied with power via the cable itself. The inner conductors in the same pair of tubes used for transmitting the high frequency band are also used for power supply. By means of a combination of high-pass and low-pass filters at each station, the power supply and the h.f. signal are separated. Rather high voltages are used for this power supply, about,000 volts between conductors, i.e.,000 volts to earth. fter this rapid survey of the construction of the coaxial amplifier equipment, a number of difficulties which the designer meets when designing equipment of this type will be described. In this way there will also be a possibility of answering the question of how the rapid development toward larger bandwidths which has been witnessed in the past 0 years will continue as far as coaxial systems are concerned. The Line mplifier The equipment which is the most difficult to build in a coaxial repeater equipment is without doubt the line amplifier itself. One of the difficulties is the negative feedback together with large bandwidth and high frequencies used. For the Mc/s system, a telephony band is transmitted which goes from 0. Mc/s to Mc/s. In order that the amplifier shall not self oscillate, the gain in the feedback loop must be controlled both in magnitude and phase within the appreciably greater frequency range of 0 kc/s to 00 Mc/s. To be able to satisfy the given conditions within this increased frequency range, very stringent requirements must be placed on good mechanicalelectrical construction and also on the electrical components. The capacitors, for example, which must be rather large to satisfy attenuation and phase shift requirements at the low frequencies, have an inconvenient tendency to become small inductances at the upper frequency limit. The component which decides what is possible as far as bandwidth is concerned is, however, the electron tube. Stringent requirements are placed on it as regards figure of merit, harmonic distortion, noise and length of life. For international circuits the CCITT requires that the noise contribution in a telephone channel which is due to the h.f. line shall not exceed pw/km, measured psophometrically, when referred to a point of zero relative level. Such line noise is due to two sources:. Thermal noise. Intermodulation noise

110 The thermal noise in turn is partly due to the cable and partly due to the input stage of the line amplifier. If one considers that one can design amplifiers with ever-increasing bandwidths while retaining the noise factor, the consequence of having an increased number of amplifiers in tandem is that the input level must be chosen to be increasingly higher. On the other hand, intermodulation noise is formed in the output stage of the amplifier. It will be understood that harmonics from a telephone channel can give rise to interference in other channels. In the same way, intermodulation products which are formed as combinations of different frequencies give rise to interference. ll these, however, are individually so insignificant that only the sum of all interference is noticeable and only then as noise. This noise increases with the number of amplifiers, exactly as was the case for thermal noise. Certain harmonic distortion products add up on a voltage basis from amplifier to amplifier. In addition the intermodulation noise increases by a factor which lies between the square and cube of the number of channels. fter what has been said here, it will be understood that the harmonic distortion characteristics of the output stage are of appreciable importance. The negative feedback which was necessary to keep the gain stable is no less important when it is a question of reducing the intermodulation noise. Fig. shows how the input and output levels per telephone channel may be varied as a function of the number of channels if CCITT noise requirement of pw/km shall be fulfilled. The graphs have been calculated assuming the following:. CCITT standardized cable is used. Constant negative feedback (fifi) is used. There is constant total harmonic ratio ( kr ) at mw output. There is constant noise factor By constant, it is understood in the above assumptions that with increasing amplifier bandwidth there are the same requirements as regards feedback, total harmonic ratio and noise factor. s far as harmonic distortion is concerned, the second or third order harmonic distortion noise can be dominating. The assumption has therefore been presented in a more general manner, that is: a) In the case where the second order harmonic distortion alone gives the dominating noise contribution, then l:, + ii(i. Nepers where ub is the amplifier feedback in Nepers. N y~^~^ *Kw^ P^\^ L = 0 km k + I'/i =. N ka + PP =.0 N Noise factor 0. N ^r-t j i, ; ^ i Fig. Input and output levels of a coaxial line amplifier as function of the number of channels a output level b input level x» JBS T *' i Number of channels

111 Number of channels b) In the case where the third order harmonic distortion alone gives the dominating noise contribution, then ' f' Ob / /J / fe» Mc / ^:I + fifl = '.0 Nepers where /tfj is the amplifier feedback in Nepers. It must here be considered that either a) or b) apply. The difference between the output level and the input level graph gives the possible gain. It will be seen in fig. that this decreases rapidly with increasing number of channels. cursory examination gives the impression that the stated assumptions do not give the possibility of further trebling the circuit capacity when reducing the repeater spacing by a half. «< >«e k, Noise L + /</* + /< actor = S Ok n =. SN -.0 t J - 0. N To determine what the conditions are, the number of channels as a function of the number of amplifiers on '/it of the hypothetical reference circuit have been calculated from the same assumptions applicable for fig.. The result has been given in fig.. The position as regards the Mc/s and Mc/s systems has been inserted. /z 00 Number of amplifiers Fig. X Number of line amplifier stations per 0 km for different numbers of channels Points a and b denote existing conditions for Mc/s and Mc/s systems respectively It will be seen that the given assumptions correspond with the development which has so far occurred. More interesting, however, is the linear characteristic of the calculated graph up to to 0,000 telephone channels. This characteristic indicates that the previously mentioned assumptions are still sufficient for a further trebling of the circuit capacity by halving the repeater spacing. bove 0,000 channels, the linear relationship ceases and the requirements must be more stringent. n analysis of the assumptions concerning cable type, total harmonic ratio and noise give direct answers as to how coaxial systems of the future will continue to be built out for an everincreasing number of channels. The assumption that we should attempt the development of possibly an,000-circuit system using the same type of cable depends on the fact that these cables are already in the ground. By conversion of Mc/s systems to Mc/s systems on an existing cable, it is possible to increase the circuit capacity at a plant cost which is only a quarter of the cost of obtaining the increased capacity by putting in new cable equipped with Mc/s systems. When the Mc/s system is fully occupied, if it is possible to make a new conversion, this time to a 0 Mc/s system, it can be estimated that the increased circuit capacity could be obtained at a cost per circuit which lies 0-0 % below that of a new installation. The condition is of course that the 0 Mc/s system is made for the normal CCTTT cable. The assumptions concerning feedback, harmonic distortion and noise factor fall back almost exclusively on the active elements that are used in the line amplifiers whether they are tubes or transistors. In table will be seen what are the requirements of the tubes that have been used in Mc/s and Mc/s systems. Table. Characteristics of different types of electron tubes developed for wideband purposes Tube type Frequency Mc/s Figure of merit Mc/s lsr + Up Nepers 0 B Da Da = ). 0=). 0=). 0=). (r = ). (r = ). 0=) N N 0* 0* 0. l>=).0 (r = ) *R L = 0 il

112 issipation Watts sink at C N0S * o WXI/SXCo ZN0IS N X NIS i N& x NI$0*o X NW<f TK0 N*ZX < PT00 NI < x Ge o Si NfS x /V/S/K HI<* o Nll* x N0 o It will be seen from the above table that the electron tube type Da would not be adequate for an h.f. line with 0 Mc/s as the upper frequency as k, + u[) does not come up to the required. N. For this purpose we require a tube having about x 00 = 00 as figure of merit. s far as transistors are concerned, these have advanced rapidly, but earlier, proved types such as N are hardly adequate for Mc/s systems. For Mc/s systems the harmonic distortion characteristics and figures of merit are too low at least if a repeater spacing of. km is desired. What possibility is there of designing tubes, tetrodes, pentodes having figures of merit of the order of 00? There are two fundamental ways of increasing the figure of merit: 0!* NS N ) by increasing the anode current drawn per unit area of the cathode ) by reducing the grid-cathode separation. Mc/s Cut-off frequency Tube 0 has a current density of 0 m/cm'-'. It should be possible to double, possibly treble this value, but then probably the tube life would be unfavourably affected. P'g- X The position in as regards transistor cut-off frequency and permissible dissipation The grid-cathode separation of tube 0 is about 0 iim. t these small distances the grid wires must be made very thin and the grid wound with very little lead so as not to cause too uneven a field distribution at the cathode. Nowadays, grid wires of //m diameter about a tenth of the thickness of a human hair are used, and the technically possible limit should lie at about - fim. greater reduction of the grid-cathode separation cannot therefore be considered. s the figure of merit only increases with the cube root of the factors mentioned, it will be understood what technical difficulties must be overcome if a trebling of the figure of merit is to be obtained. Possibly the tube capacitances can be reduced by using a v.h.f. type construction of the electrode systems along the same lines as the high frequency i.f. triodes in radio link systems. The conclusion must be that by marshalling all resources it may be possible to design a tube having the desired characteristics. fter that, this branch of tube technique probably cannot be developed further. s far as transistors are concerned, these have been developed in a few years to an extent that few people had imagined as regards h.f. performance and power dissipation. The diagram in fig. gives a survey of the transistor types available on the market. The cut-off frequency shown in the figure is considered measured in a grounded emitter circuit and is not directly comparable with what we know as figure of merit for an electron tube. Comparative values are obtained by multiplying the cut-off frequency by a coefficient lying between s and ty»- Nowadays it can be said that the highest frequency transistors have figures of merit which are almost comparable with those of electron tubes. On the other hand, transistors at present have worse harmonic distortion characteristics. In a few years the development on the transistor front should have come so far that transistors will be available which permit the construction of 0 Mc/s line amplifiers having adequate stability and harmonic distortion characteristics. In choosing between tubes and transistors, the designer prefers the transistor solution because the mechanical dimensions can be made so small that the problem of stray inductances and capacitances from the wiring can probably be avoided. Finally, the problem of remote power feeding of transistorized amplifiers is simpler to arrange due to the smaller amount of power used.

113 \ Summarizing, the following can be said: It is extremely probable that with the help of transistors, coaxial amplifier technique can further master the increase in the width of the frequency band to about 0 Mc/s. ny further increase in the bandwidth is thereafter very improbable. It will be seen that where crosstalk sets the limit for symmetrical pair systems, it is the attenuation which will stop the continued development of coaxial cable systems. Radio Link Systems s regards radio links having high channel capacity per radio channel, mostly,000 Mc/s and,000 Mc/s systems have so far been used. COR prescribes a maximum of,00 telephone channels per radio channel for these systems. frequency range in the,000 Mc/s band which was still free for radio link purposes was allocated for eight radio link channels by the CCIR in. This system too was allocated a maximum capacity of,00 telephone channels per radio channel. There are no radio link systems having more than,00 telephone channels per radio channel standardized by CCIR at the present time. To increase the capacity by using higher radio frequencies does not appear to be possible with the present repeater spacing, as the transmission properties of radio waves of frequencies above to Gc/s are too sensitive to atmospheric disturbances (absorption). The question is therefore whether it is possible or desirable to increase the number of telephone channels per radio channel. CCIR have this question on the agenda for study, as it is considered that it is an economic and a network planning advantage if appreciably more telephone channels could be transmitted over a radio channel.,00 channels is under consideration as there will then be agreement in the number of channels of coaxial cable systems and radio link systems. Certain manufacturers have experimental links in operation having a capacity of,00 telephone channels per radio channel. The result of these trials appears to show that it is possible to realize systems with the mentioned channel capacity within the,000 Mc/s band. In these trials, it appears to be necessary to increase the frequency separation between the radio channels to about Mc/s where CCIR states 0 Mc/s for the normal,000 Mc/s systems. The increased channel capacity must therefore be paid for by a reduction in the number of radio channels if in the future it is desired to keep the radio frequency bandwidth within the 00 Mc/s standardized by CCIR. It should therefore be observed that the situations for radio link circuits and for coaxial cable systems are completely different. In the case of radio link circuits the total radio frequency band is limited. n increase in the width of the different radio channels must therefore occur at the expense of the number of radio channels, which means that for a given aerial system, constant repeater spacing and given transmitter power, the number of telephone channels per frequency band remains practically constant. Now aerial systems, radio link towers, roads etc. contribute a not unappreciable expense to radio link circuits and these costs are not consequently divided between more circuits by increasing the channel capacity per radio channel. The economic pressure for an increase in channel capacity should therefore not be so pronounced as in the case of the cable systems. The technical difficulties of increasing the channel capacity per radio channel are great, but reasonably not limiting. On the other hand, multipath propagation prevents radio channels with too wide a relative bandwidth from being transmitted. Where the limit lies in this case is difficult to say, but it appears, despite everything, as if an h.f. bandwidth of Mc/s will be the ultimate goal. In this way, the limit of the channel capacity will stop at.00 channels per radio channel. * 0

114 Mc/s on coaxial cables. Mc/s on radio links We therefore see that radio link systems, too, are limited. What is most difficult in the long term is the limited frequency space. Problems arise where different routes cut one another or where the radio link beams converge on large towns. In US, where difficulties of this type are already appearing, there were 0 i; km of telephone channels and 0-0 :i km TV channels in the radio link network in 0. To illustrate the situation in Sweden, figs. and, show the coaxial cable and radio link networks in and as planned for. s one thus sees limits of different types for coaxial cable systems and radio link systems, it is not to be wondered at that over the whole world, future systems are being worked upon which are not affected by the difficulties which present systems have, i.e. for coaxial cable systems, problems of attenuation and for radio link systems, the limited frequency range which is available and which finally depends on there being so many communication systems using the ether as the common transmission medium. Waveguides have been known for a long time and these possess such characteristics that the above mentioned difficulties are eliminated. Fig. X Coaxial cable and radio link networks for telephony in Mc/s on coaxial cables. Mc/s on radio links Mc/s on coaxial cables - - Mc/s on radio links Waveguide Technique a. Normal waveguide technique It is quite understandable that if one wants to transmit electromagnetic waves in a waveguide, there must be a certain minimum cross-sectional area of the waveguide in relation to the wavelength. The waveguide thereby behaves as a high-pass filter. If the frequency is increased, gradually several wave configurations will be possible simultaneously. In the case of normal waveguide technique, it is usual to choose the waveguide dimensions so that only one wave mode can exist. Waveguides designed after this principle are relatively uncritical to small tolerances in the dimensions as these only make themselves felt as impedance errors. t,000 Mc/s, a rectangular waveguide has about db attenuation per kilometre. Such an attenuation could be accepted for long distance transmission but the waveguide cross-section would be just over X cm and therefore such a solution must be considered as unreasonable from an economic point of view. If a high transmission frequency is chosen the waveguide dimensions are reduced. t,000 Mc/s it is sufficient to have a X. cm waveguide but at this frequency the attenuation is on an average 0 db/km. In other words: Normal waveguide technique cannot be used for long distance transmission. Fig. X Coaxial cable and radio link networks for telephony in b. "Multi-mode" waveguide technique If a fixed waveguide dimension and a given wave type are considered, it is seen that when the frequency increases the attenuation first decreases and then again increases due to the skin effect in the waveguide walls. In the case of circular waveguides there are, however, several wave modes, TE, where the electric field lines do not terminate in charges on the waveguide walls but are closed on themselves (see fig. ). In the case of these waves it is therefore not a question of a transfer of charge along the waveguide, and the effect of increase of attenuation which occurred due to the skin effect in other types of waveguide therefore does not occur. s a consequence of this, these waves show a steadily decreasing attenuation with increasing frequency. It is therefore possible to obtain small waveguide dimensions and at the same time have low attenuation. If an attenuation of db/km is required, which is approximately that which can be obtained with a microwave radio link system, it is possible to obtain this at 0 Gc/s with a waveguide diameter of ".

115 ^ Fig. Field distribution for the mode TE 0 i Magnetic field lines Electric field lines X electromagnetic QOl l Wrf-- ^ sm '.-V.','.'.'.'.'.'. I' ////////.'..'.. -. t/rrrn- :S- ^^r-?! -o,oi ot > c,<po There is, however, a weakness of the wave type TE, due to its nature. When it can exist there are several other types of wave possible simultaneously. If one tries to find a waveguide diameter which gives low attenuation there is simultaneously a large number of possible modes. In the case of a " diameter waveguide and / = 0 Gc/s the number of modes is greater than 0. If. at one end of a waveguide, a pure wave of type ' 0 is injected, a major part of its energy will be transformed into other possible wave modes if there are the least irregularities in the geometry of the waveguide. The result of this transformation is an increased attenuation of the main wave. It should also be noted that the transformation described is also reversible. If the non-desired wave is not therefore rapidly attenuated, a return to the original wave can give rise to difficult interference phenomena. Most severe as regards signal distortion is the interference which has a long wavelength. This interference is formed between the waves TE m ^ TM n where the wavelength of the interference is of the order of km. For intereference between the waves of type TE in is only of the order of 0. to.0 m. T n, the wavelength \TEOI \TE 0 VTEi To prevent this interference arising, one first attempts to make the waveguide as geometrically perfect as possible so that no irregularities occur which give rise to wave change. R.M.S. (D mslx D min ) < 0 : mm... Second, the impedance of the waveguide wall can be changed in such a way that the desired wave is favoured compared with the other wave modes. This is done by, for example, coating the waveguide wail internally with a helix or a thin dielectric film. These methods have good effect and give quite uncritical conditions in such waveguide bends which must be made if, for example, it is desired to follow a railway line. The interference which has a short wavelength is, however, not removed as these methods have not managed to damp out the interfering wave on the short interference stretch. The greatest problem should therefore be to keep the waveguide straight in small lengths of about 0. to. m where the tolerances on straightness are of the order of to /00 mm xio X0 Mc/s Fig. x ttenuation as function of frequency for wave modes TE 0 i, TE 0 and TE 0 in a circular waveguide of " diameter The figures given on the graphs denote the number of possible modes. With regard to these tolerances, the handling and installation of such a hollow conductor is a problem of the greatest degree of difficulty. Despite all measures, one obtains, however, a very unfavourable signal-tonoise ratio. modulation method which permits a regeneration of the signal is necessary. P.CM. has, for example, been chosen in the trials now proceeding at Bell Laboratories. The work has not yet progressed sufficiently far and therefore one can only give an idea of the system on very broad lines. ccording to the preliminary \

116 plans of Bell Laboratories, the following figures indicate what possibilities the waveguide systems offer as regards circuit capacity.. Total radio frequency band: 0 Gc/s-00 Gc/s. Radio channel bandwidth: t Gc/s: 0 Mc/s t 00 Gc/s: 0 Mc/s Problems of group delay are most easily solved by maintaining a smaller bandwidth at the lower frequency limit. In judging these bandwidths, it should be remembered that P.C.M. is used i.e. a modulation method requiring about times as much frequency space as single sideband.m. The channel capacity per radio channel is therefore less than one would think, i.e.: t Gc/s:,00 telephone channels/radio channel t 00 Gc/s:,000 telephone channels/radio channel The number of radio channels that can be sent over a waveguide is, as yet, uncertain but the total capacity per waveguide will certainly exceed 00,000 telephone channels. Bell Laboratories are working very hard on waveguide systems and estimate that they will have the first trial system ready in -. In 0, the first production systems should be in operation. It is, of course, too early to forecast when the first waveguide system will come to Sweden. It should be remembered that waveguide systems are expensive as regards plant cost and certainly also regarding maintenance. Only when these systems are first occupied with sufficient traffic will they be profitable; traffic demands of telephone circuits or corresponding bandwidths for other traffic requirements should therefore be necessary if waveguide systems are to compete with systems of more conventional type. Terminal equipment When modulating telephone channels to such wide bands as, for example, the Mc/s band, the modulation is carried out in several stages. From the filtering technique point of view, it would be impossible to modulate the telephone channels to their final position and this would also require an unreasonably large number of different carrier frequencies. To obtain the Mc/s line frequency band would require,00 carrier frequencies in the case of Frequency band for through connection super- master- kc/s group Mc/s coaxial cable system Frequency band for line equipment Kc/s Mod -0 kcs mast "- group Mod 00-circuit system (radio link) 00-cireuit system (radio link) kc/s 0 kc/s - kc/s Mod supcr - group Mod Mc/s coaxial cable system J0-circuit system (symmetrical pair cable), 0-circuit system (symmetrical pair cable) 0-^0 kc/s 0 kc/s kc/s Fig. 0 X Survey of the frequency bands for through connection standardized by CCITT T 0 0 kc/s group <Mod' 0 kc/s channel Mod -circuit system (symmetrical pair cable -circuit system (symmetrical pair cable) 0 kc/s 0 kc/s 00

117 F'g- M X Hypothetical reference circuit for Mc/s coaxial cable system v -o ^> } n Modulation equipment "»» channel ^^ basic group basic group basic supergroup basic mastergroup ^ basic "* supergroup ^ basic ** mastergroup >. basic supcr- * mastergroup >^M D~Q QH]~Q ^O -^ / reference circuit direct modulation whereas modulation in stages would require only. survey is given in fig. 0 of the modulation stages and the necessary relationships between the different carrier systems. s CCITT has standardized the different stages of modulation, it is possible to go from one h.f. line to another without demodulation to channel frequency. The h.f. lines do not even have to be of the same type as far as number of channels is concerned. There is always a common level where through connection can be made. Great savings can be made in material due to this possibility of through connection. It will be seen that using the chosen principles there are no great difficulties in extending the line frequency band to cover an ever-increasing number of telephone circuits e.g. nine supermastergroups belonging to a 0 Mc/s system. This fact of carrier systems forming a whole network with through connections at different levels makes it very difficult to decide what requirements should really be placed on the individual links to ensure that CCITT's requirements concerning an international circuit are maintained. This has led to CCITT proposing so-called reference circuits which are hypothetical circuits of,00 km length and with a specified number of terminal and through connection points. The total permissible noise for a complete reference circuit is 0,000 pw, of which,00 pw has been allotted to the h.f. line equipment, irrespective of whether this consists of cable systems or radio link systems. CCITT have also defined different reference circuits belonging to different types of carrier systems. reference circuit for a Mc/s system is shown in fig.. It should be noted that the whole reference circuit consists of three identical parts and only Vs has been shown in the figure. The many modulations and through connections (0 in a complete Mc/s reference circuit) demand that the band-pass graphs of the individual modulation stages are maintained within very narrow tolerances. The most stringent requirements are placed on the equipment for the higher stages of modulation as these occur most often in the line. New filter calculation (insertion loss) methods and also new types of measuring instruments have had to be introduced so as to be able to satisfy these more stringent demands. t the Plenary ssembly in New Delhi in 0, CCITT took a new step in making the first proposal for an intercontinental reference circuit. Whereas the international hypothetical reference circuits consist of three voice frequency to voice frequency links, the intercontinental reference connection is considered to consist of not less than such links. The total length has been made,000 km. Now it is quite certain that not quite so many through connections per circuit are considered as in the case of the normal international reference circuits but in the first proposal there are supergroup through connections in any case. s the requirements which were originally placed on an international circuit as far as equivalent should still be maintained, it will be understood that this new intercontinental reference circuit means a tightening of the requirements, especially on the channel attenuation graphs. Study Group XV which deals with these problems has already made proposals in Geneva, November for such more stringent requirements concerning equivalent. s a manufacture of carrier equipment one must be glad that the earth is no larger than it is. 0

118 Planning of Multi-Exchange Networks with id of a Computer III. Planning of Junction Circuits in Multi-Exchange Networks. Some Fundamental Principles Y RPP, TELEFONKTIEBOLGET LM ERICSSON, STOCKHOLM UDC.. LME 0 Methods aimed at simplifying the estimate of the future volume of traffic between exchanges in a multi-exchange area after modification of the network structure were presented in Ericsson Technics No.,. In Ericsson Technics No.,. it was shown how the number and locations of the exchanges, and the boundaries between them, can be determined by starling from a subscriber inventory. condensed account of these two papers was given in Ericsson Review No.,. The present article follows on the previous publications and gives a preliminary survey of two of the fundamental principles which can be employed when planning junction circuits. This will be followed by more extensive accounts at a later date. For the planning of junction circuits in a multi-exchange network, one must assume that the exchange locations and boundaries have been established and that the flow of traffic between the exchanges is known. From these and other data, relating to costs etc., a junction diagram must be drawn up, with the necessary specifications, such that the costs of junction cables and switching equipment are as low as possible. Examples of the structure of junction circuits in a network of nine exchanges are shown in fig.. Fig. (a) shows direct circuits between all exchanges, fig. (b) an arrangement by which connections must pass through a tandem stage. The exchanges are divided among three tandem areas as follows: Tandem area 0 Exchanges.,,,,, In a tandem area all exchanges are linked to the tandem stage by two-way circuits, whereas connections between a tandem stage in one tandem group and an exchange within another tandem group can be set up only in one direction (see fig. (b), in which this condition is marked by arrows). Fig. (c) shows a network in which connections pass through two tandem stages. In the same way arrangements can be made for the use of three or more tandem stages. Fig. x S Example of junction circuits in a multi-exchange network O exchanges D tandem stages Junction Matrices These various arrangements can be drawn in the form of a junction matrix which, for the example chosen, is shown in fig.. In this matrix the numeral indicates that a junction exists, 0 that no junction exists. 0

119 -i \ T rom\ 0 Fig. I )irect routes Tandem routes 0 - Junction matrix representing the circuits in fig. In making up this matrix it is not necessary to assume, as in the example above, that all direct circuits exist. One may, for example, decide from the outset that certain exchanges shall be linked exclusively via one or more tandem stages. In such case a zero is written in the corresponding square in the matrix. One may alternatively decide from the outset that certain junctions shall consist of direct, low loss routes without possibility of passing through one or more tandem stages. In such case the corresponding square in the matrix is marked. ccordingly the type of junction is indicated by 0 if there is no direct junction between two exchanges and all traffic must therefore pass through one or more tandem stages if the junction is a high loss route if the junction is a direct, low loss route. In the same way, in fig., the numeral in row and column 0, for example, indicates that exchange belongs to tandem area 0, and the numeral 0 in row and column that exchange does not belong to tandem area. zero in row and column, finally, would indicate that no tandem circuit exists between tandem stage and exchange. This means that the junctions to this exchange will either be direct and/or must pass through two tandem stages from all exchanges in tandem area. Junctions via two or more tandem stages are marked in a similar manner. junction matrix made up in this way constitutes the basis for the provision of switches and circuits in a network consisting of a given number of tandem areas of a given size. In the same way one can investigate other alternative solutions and, from the resulting suboptima, an approach is finally made to the optimum economic solution. But all this involves very lengthy calculations even in comparatively small multi-exchange networks. ny mechanization of this work is, of course, a welcome relief. For computer programming the junction matrix exemplified in fig. is of fundamental significance since, in fact, it describes the logical scheme to be followed in the calculations, and at the same time enables the results to be presented in a systematic form. It also facilitates the manual calculations, especially of the volumes of traffic on the various routes within the network. Systems of Equations Formulae are required which indicate the relation between the number of junctions, the traffic, and the grade of service. On routes with random traffic this generally involves no difficulty. It is on tandem routes with degenerated traffic that certain problems arise. These are due not so much to the fact that an exact solution for such traffic does not yet exist, but above all that the available methods of approximation which are satisfactory for practical purposes are very laborious if the circuit design is to be based on economic principles. This applies even to one of the best known approximations, namely Wilkinson's formulae, the practical use of which requires a lengthy process of interpolation between two families of curves. ccording to Wilkinson's method one determines from the mean traffic, M, and variance, V, on a route an equivalent traffic. *, and an equivalent number of circuits, n*, from the two equations * E(n*, *) = M * M -M + l+n* + M~* after which the number of junctions on the route can be calculated. 0

120 Number of junctions on a last choice route n investigation carried out in consultation with Mr. B. Wallstrom, however, has shown that the aforementioned difficulties can be circumvented by calculating the number of junctions, m, on the route from the expression * E(n* + m, *) = 0 where is a predetermined value for the grade of service on the tandem route, and then choosing as parameter the degeneration of the traffic defined as V M variance of the traffic mean traffic In this way the number of circuits on a tandem route can be represented by a family of curves having the appearance shown in fig.. This figure shows the number of circuits on last choice routes as function of the mean traffic for different degrees of degeneration at a predetermined grade of service E = Other data required for the calculations, such as "equivalent traffic" and "equivalent number of circuits", can well be represented in the same way. For calculation of the number of junctions on high loss routes, a knowledge is required also of the "slope" of these curves, i.e. the increase in number of junctions on the tandem routes for a small increase of the traffic. Explicit expressions for these conditions can be presented from Wilkinson's formulae. Fig. shows by way of example the result of a calculation for E Mean traffic Fig. X The numher of junctions, m, at an exchange as function of the mean traffic, M, and de- V generation, rj, at = 0.00 according to Wilkinson's system of formulae. The calculations for this diagram were carried out with a computer. Calculations From these and similar families of curves describing other values of grade of service, the number of junctions on direct and tandem routes can be calculated as follows.. The increase in the number of junctions on the tandem routes for a small increase of the traffic is determined on trial.. With the guidance of this increase and the marginal cost per junction on different routes, the number of junctions on all high loss routes is determined from the inequality (E(n- \)-E(n))> h^i h h B. >(E(n)-E(n + )) 00 M Mean traffic Fig. X dm Increase in number of junctions, TTJ, on a last choice route for a small increase in the mean traffic at unchanged degeneration and,, where B = marginal cost per junction on direct routes B,. B marginal cost per junction on associated tandem routes /(,. h = increase in number of junctions on respective tandem routes for an increase of traffic on those routes of erlang at unchanged V degeneration - - and predetermined value of M congestion.. Thereafter the mean traffic and the traffic variance can be calculated on all routes with degenerated traffic.. From the resulting figures new values are determined for the magnitudes under point (cf. fig. ), and the calculations are iterated until the number of junctions on the high loss routes undergoes no further change.. The traffic distribution in the network has thereby been found, and the number of junctions on the last choice routes can be determined (cf. fig. ). The principles outlined above constitute the most important basis for an economic calculation of the structure of the junction circuits, whether done manually or with a computer. more extensive treatment related to practical examples will be presented in a coming issue, when questions concerned with the presentation of the results will be dealt with. 0

121 \ Practical pplication of the Planning of Multi- Exchange Networks with id of a Computer Exchange Locations and Boundaries Y RPP & Y OLLUS, TELEFONKTIEBOLGET L M ERICSSON, STOCKHOLM UDC.. LME 0 The method of planning a telecommunications network described in Ericsson Review No.,, has been employed in drawing up the general plan for extension of several existing networks, one of which was the bo network in Finland. The present article, which presents a resume of the bo plan, illustrates the practical use of the method. Until bo had only one telephone exchange in the centre of the town. In that year a second exchange, Martinmaki, was opened for service. The town of bo, however, already extends over a distance of - miles and new residential areas are continuously being built around its periphery. The administration has long been planning to divide the network into several exchange areas. joint study was therefore made by the administration and L M Ericsson in order to obtain a framework for the detailed planning of outside plant and exchanges in coming years. The principal data for the study were provided by the administration, while L M Ericsson made the necessary calculations.. Basic Data Number of subscribers t the end of the bo subscribers were served by two exchanges: Centrum (Exchange ) lines Martinmaki (Exchange )..,00 Total,00 lines It was decided that the general plan should cover the situation in. The number of subscribers in was estimated on the basis of building plans and subscriber growth in the network during recent years. The subscriber prognosis is shown in fig.. In the square grid, the axes of which have the same direction as the streets in the centre of the town, is marked the estimated number of subscribers in, namely,00. The central exchange, which contains the long distance stage, is designated and the Martinmaki exchange. The subscriber inventory is fed into a computer with indication of row, column* and number of subscribers in each square. The traffic The junction circuits have little effect on the exchange locations and boundaries. Only a rough estimate, therefore, is needed of the traffic between subscribers in different parts of the network. The traffic from one subscriber to another within the bo area was estimated on the basis of traffic observations at the existing exchanges. For every pair of exchanges the computer is fed with data of the total traffic between two subscribers situated in separate areas. * Row and column numbers are not marked in the figures. 0

122 \ s. 'I v S \, ' ". i I s \ i 0 0,0 - _,_ g y ' iu. uh «> v IE C, '~ _ u 0 SIT «>. ^ - \ ' I r i i M V i ~T i i - i r ij' \ [ N^ir^ J 0 X ^ ' -J\J i 0 0 j, 0,/* >[' ' 0 tj _Li! 0 "S js^sjjo,^ ^cptpir l 0 n S ibi - 0 e r i -^ := i l V V i S- > > =te^\ L ' 0! 0. ' 0 TO : -. 0 J.J [ ; tor '. 0 ' z 0 V V V!\ i i r I j T- r 0 0 S 0 i "- S i i?f< r- : " = E" J-? >r r>- - l: 0 0 ' - Q 0 ' \h 0 0 > r V -! ^ /, \ S S V ^ i J SI? ja 0 u to 0 0 ^ \% 0 0 J Of. C tw*r ^ IT IT - SO" TS. 0 0 lab. 0 " < fj K i. E : ^hx~ j. r> k - - "* -. ' N V c, *^-fe=- '0 0 0 d 0 0 "ETJJ 0 t- 0 i -- 0 E V. : - ^ S TV 0 0 JL T 0 ' ie 0 -^ ^ J '. 0E E. 0 JO - f / 0 0 i 0 0, -(+- J *L E T: S ^ s N i \ ' ". S, E ^ 0 C E,( 0 ioo J l w;, 00 " 0 0 i hj- 00 l^l E TO IT 0 LL0-0+" - BE \\ v \ 0 -" : FOE 0 0C 0 ',". 00 "so" Tcr es B -^ tt C 0 * lu r <? v \ i - E i / f / \ Ss i\ X E V»,. r J0 0 0 "»~- I fto p ff J-l + f 0 rl ^ ^ > UO ^^ ^e e 0 v. 0 ^ H l ic ' i N '(" \»; ^ '» 0 0 C 00 -H c *f f \\ T TO fr ) -* ' ' ILL ^ H 0 0 ^ V H ijs T 0(0 D "0 -scum: 0 B B0_ S 0! ^ $ \\ \ \ i f v \ \ i / y ' \ I / \\ \ ' i 0.? 0 BE _ i i if I h "" 0 I' f ^ iv, IE o N j PV { jo F ^ E" / ' 0 0 <\ ^ '\ / 'If? > I *' JJ- J L " * ^ ^ * SC U H, 0 TF 0! s 0 t-r SO <* 0 - -!* ET- g -V, El 0 -. E re- - J. 0 V -F 0 li - ST 0 '! El.E E 0.-^?' " "^~~ 0, 0 - it 0 / il, - f %?S _ T 0 ' u I i v \. JL ^ k \ \ V ^. 0 --» 0 E ji. it S ^ E - IE 'i : I - ' -*:"-- V, NV u», e V /' ^ V- ( ' \ I' V \,0 \ f f \ - '- i-r g^ g= F ' ' - '' E> - 0 V s / l\ \ \ y i E. i 0 ^ 0. ^^ 0 - > V =, H«. lb 0 V ^ a -" _- 'X 0 -re. 0 < Vs b >- / ^ -J I -? n il-. 0 \ \. J E i J ^ ^ * 0 -^L. B \ V lv ' r // ^ J_ 0 r ^ ^ - ) 0 r i V ( ) ^ l i, J N i < I X < 0 0! p / r ' f= \ s? ~r lu 0 / ' =^ r s, 0 l.j 0 /" X 0 ^ ' I 0 ^ "-I N 0 0 I r 0 ' 0

123 Costs In order that the costs of the various parts of a telecommunications network may be added together and a comparison made between total costs for different alternative solutions, attention must be paid to usage time, maintenance, and rate of interest. This can be done by introducing a present value factor, //, defined by the following expression:,«= + + r\ r r = rate of interest in % 00 s = estimated usage time u = annual maintenance cost as per cent of first cost. Outside plant For the purposes of the calculation the cost of the outside plant must be indicated per pair-kilometre both for junctions and for primary cable network. This cost is governed by the types and numbers of pairs of the cables employed. The administration gave the following cable data: for all junctions 00-pair cable of 0. mm wire diameter, for the primary network, exchange, 00 pair/0. mm, for other exchange areas, 00 pair/0. mm and 00 pair/ 0. mm. The wire diameter is determined according to the Finnish standards. The cost per pair-kilometre for junctions and primary network is fed into the computer. Subscriber inventory, traffic data, pair-kilometre cost for junctions and primary network, the locations of the fixed exchanges and the number of exchanges with variable locations are the input data required by the computer. Based on these input data the computer determines the exchange locations and boundaries in such a way that the costs of subscribers' and junction cables are as low as possible. The exchanges The cost of a telephone exchange consists of building and site switching equipment installation In the bo network the costs of the exchanges were based on L M Ericsson crossbar price lists. Building and site costs were supplied by the administration.. Calculation The total cost of a telephone network depends on the number of exchanges in the network. The number of exchanges in the network is, as stated, one of the input items required by the computer. For any given number of exchanges an optimal solution is obtained as regards their locations and boundaries and the corresponding total cost can be determined. The same calculation is made for different assumptions as to the number of exchanges, after which the most appropriate solution is chosen. 0

124 The input data for the exchanges and their locations in the bo network included two fixed exchanges exchange / (Centrum) and exchange (Martinmaki), the remainder being variable. fter comparing the costs for, and exchanges, the -exchange alternative was found to result in the least cost. The geographical conditions also favour this alternative as basis for future detailed planning. The cost ratio for the three alternatives was as follows: lternative ( exchanges) 00 lternative II ( exchanges) 000 lternative III ( exchanges) 0 s will be seen, the differences in cost are virtually negligible. LT. 0 ug. Table. Determination of exchange locations and boundaries in relation to junction cables. Exchange I Location mean length no. of subs. Boundary Distribution Cost for junctions Exchange Location 0 0 mean length no. of subs. Boundary Distribution Cost for junctions Exchange Location mean length no. of subs. Boundary Distribution Cost for junctions Exchange Location mean length no. of subs. Boundary Distribution Cost for junctions Exchange Location mean length no. of subs. Boundary Distribution 0 Cost for junctions Exchange Location 0 mean length no. of subs. 0 Boundary Distribution 0 Cost for junctions

125 l 0 IC U 0 H 0 0 i 0 U : e ; o & 0 00 c \. 0 C I 0 )* i e M 0 0 ( K ' " IOC l T) 0 0 a SO C 0 IOC ~ IG 'i l l_ i C I H :a < 0 0 or IOC to C o * (D> > in I i IS 'i 0 L ft S i *\.*C* \$J"-r S a 0 u 0 :e e 0 L f, H e 0 I l H ()0 0 l t? i l U 0 i. i 0 C 0 0 e l b i t i Fig. Exchange locations and boundaries under alternative II 0

126 Fig. Plan for extension of bo telephone network up to the year X 0

127 \ Exchange Location mean length no. of subs. Boundary Distribution 0 0 Cost for junctions Table shows the output data delivered by the computer for alternative II. The geographical data, i.e. the exchange locations and boundaries, in table have been inserted in the subscriber inventory in fig.. Data for exchange /: location indicates that exchange / shall be located in the square with column no. and row no.. N.B. For the bo project the subscriber inventories were drawn on a 00 X 00 m grid. But this subdivision was found to be unnecessarily fine for the subscriber density in question. For treatment in the computer, therefore, the scale was doubled to produce a unit square of 00 X 00 m. This means that all coordinates indicated by the computer must be multiplied by two in order to agree with the coordinates of the subscriber inventories. The location numbers for exchange are thus X = for the column and X = for the row. mean length signifies that the mean length of the subscribers' lines within exchange area / is times the side of a square, i.e. X 00 m = 0. km. no. of subs. signifies the number of subscribers within the exchange area. boundary etc. signifies the coordinates for the exchange area boundary. The first two groups, and, are the coordinates for column and row in which the square shall lie. The next group,, signifies the row coordinate for the subsequent square. The column coordinate is obtained by adding one unit to the previous column number, which thus becomes ( + ). Multiplying all coordinates by gives the coordinates for the exchange area boundary: column row 0 etc. distribution signifies that there are 0 subscribers in the same square as the exchange, 0 at one square's distance from the exchange, 0 at two squares' distance, and so on.. General Plan for bo The general plan presented as a result of this study comprises seven exchange areas. The area boundaries obtained from the calculation for alternative II and shown in fig. have been drawn on the town plan in fig.. The boundaries from fig. have been slightly corrected to fit the topography of the town. To determine the initial capacity of the new exchanges to be installed, a second subscriber inventory was prepared, based on the present number of subscribers and divided into exchange areas as in the proposed general plan (alternative II). The numbers of subscribers in these exchange areas now and in are shown in fig..

128 The Dry Reed Switch a Sealed Contact of Great Reliability H LEVKOWETZ, B SVENSK ELEKTRONROR, S T O C K H O L M UDC.. LME The dry reed switch is an ideally protected relay contact, being enclosed in a gaslight capsule. The fact that the magnetic field acts directly upon the reeds ensures fast and reliable operation of the relay. The dry reed switch which can be controlled either electromagnetically or by a permanent magnet, or by a combination of the two has found its chief applications in telephone exchanges, calculating machines and electronic computers. B Svenska Elektronror (SER) uses rhodium-plated contacts. Endurance tests have shown these contacts to have maximum life and reliability. Introduction The most important components in telephone exchanges are the relays. modern telephone exchange may contain between and 0 relays per subscriber's line. s telephone systems have grown in complexity, stricter demands have been placed on the reliability of relays. With relays of conventional design it has been difficult to fulfil these demands under all conditions. One of the main problems has been found to be the contamination of contacts by dust and corrosive gases in the ambience. ttempts to enclose the entire relay so as to protect the contacts were unsuccessful, since the contacts were instead attacked by organic vapours from the insulating materials in the relays. The ideal form af contact protection would obviously be to enclose the actual contact in a gastight envelope while leaving the exciting windings outside the envelope. The reconstruction of a conventional relay on these lines would, however, involve many technical difficulties. Bell Laboratories found a radical and elegant solution to the problem as early as - -. The principle of their solution is shown in fig.. Fig. Two reeds of resilient magnetic material were sealed into the two ends of a glass tube, the ends overlapping and having an air gap between them. The energizing coil is placed outside the envelope. On the passage of a sufficiently strong current through the coil, the overlapping ends are mutually attracted and make contact. The design is very simple, but is completely dependent on the availability of a material which can both be sealed into glass and has suitable magnetic and elastic properties. It was in conjunction with the discovery of an appropriate iron-nickel alloy that Bell Laboratories started on the development of this unit. The first result was the switch illustrated. These switches have since been made by a number of merican and European firms. In - L M Ericsson made a thorough study of the merican dry reed switches. The main requirement was to use them in high speed relay circuits such as testing and pulsing circuits. Since these applications also called for long contact life, the investigations were concentrated chiefly on developing a switch which would allow a large number of faultless contact operations in

129 inductive circuits carrying currents of the order of 00 m. In B Svenska Elektronror (SER) started an experimental production of these switches in coordination with several departments of L M Ericsson. product was in due course evolved which was acceptable for L M Ericsson use. Regular production started at SER in 0 and has since made quick progress. Fig. The dry reed switch is extremely long-lasting and reliable. With a suitable protective coating its life is of the order of 0 s faultless operations at 00 m. Relays made with these enclosed contacts have other advantages as well over conventional relays. Their operate and release times are of the order of ms; in other words they are about 0 times as fast as ordinary relays. pplications In collaboration with its customers L M Ericsson has employed reed relays in exchange equipments as pulsing and testing relays and as tone receivers. For such applications a reed relay consists of a dry reed switch fitted axially within a specially constructed coil surrounded by an iron sheath. The unit is designed for attachment to a printed circuit board (fig. ). This is the most obvious principle for the use of the dry reed switch, and the one in which its reliability can be best utilized. But there is nothing to prevent its use in more complicated switching circuits. Several switches may, for example, be actuated by the same coil or one switch may be actuated by several windings. In this way one can form, for example, logic ND and OR circuits. But a dry reed switch may also be actuated by permanent magnets if suitably placed in its vicinity. This opens up the way to many applications in which dry reed switches in control circuits are operated by moving permanent magnets. In view of its simplicity and dependability a system of this kind would be well suited for automatic processes. V combination of magnetic actuation and actuation by an energizing winding can also lead to many useful applications. normally closed contact may, for example, be arranged by fitting the dry reed unit and a permanent magnet inside a coil (fig. ). The magnet is in this case sufficiently powerful to close the contact when the coil is deenergized. But if a current is passed through the coil in a direction such that its magnetic field opposes the field of the permanent magnet, the contact will be opened at a given critical amperage. n interesting case is obtained if the strength of the magnet in this arrangement is so adjusted as to be insufficient to close the contact but sufficient to keep it closed if the closure is accomplished by a properly directed current through the coil. This provides an arrangement by which the contact is closed and remains closed to a current pulse in one direction and is opened and remains open to a subsequent pulse in the other direction. Such a device can be used as a memory unit. In conjunction with logic circuits these units can be employed as basic building blocks in modern calculating machines and computers. Fig. Similar logic and memory circuits can, of course, be built also with electron tubes or semiconductor components. Their operating speed can in such case be stepped up,000 to 0,000 times. But the dry reed switch has other advantages. It is simple to manufacture, needs few auxiliary components, is robust and highly reliable in operation.

130 SER Dry Reed Switches The assembly of a component consisting of so few parts as the dry reed switch is fairly simple. But if the switch is to fulfil the high functional requirements placed on it, and if a high rate of production is to be maintained, reeds and glass tubes must be made of material of high and uniform quality. Particularly severe demands are placed on the straightness of the reeds, and the diameter and wall thickness of glass tubes must be kept within narrow tolerances. Glass tubes and reeds are subjected to extremely thorough cleaning procedures, and the reeds undergo tumbling, annealing, degassing and electrolytic coating of the contact surfaces. ll foreign substances are removed from the parts by chemical cleaning, hydrogen annealing and vacuum degassing. During the hydrogen annealing the temperature and annealing time must be adjusted to give the reeds the desired magnetic and elastic properties. The contact surfaces are plated with rhodium to ensure maximum wear resistance and to render the surfaces more resistant to deterioration through the breaking and making of the contact current. Before the final airtight sealing of the reeds, the capsule is filled with dry nitrogen gas containing a small addition of hydrogen. The finished product is inspected for lateral displacement of the reeds (which must not be more than 0. mm), for flaking of the contact plating, and for the presence of small particles or dust in the capsule. check is finally made that the operate and release ampere-turns are within the prescribed limits. With given dimensions and treatment of the reeds, it is their overlap and the gap between their contacts which determine the operating data of the switch." The number of ampere-turns needed to close the contact rises, of course, with the size of the gap. nd if the gap exceeds a critical value, it becomes impossible to actuate the contact owing to magnetic saturation of the reeds. If a very sensitive relay is desired, the gap should be as small as possible. But the smaller the gap, the greater is the spread in the switch data for a given gap tolerance. The operating sensitivity of the relay has a maximum for a certain overlap and falls if this overlap is increased or decreased. The release ampere-turns are also dependent primarily on the gap and overlap. The effect of these factors on the life of the switch, moreover, is difficult to assess. There are thus many factors to take into account in the design of a dry reed unit for a given function, and a compromise must generally be accepted between different, more or less incompatible demands. Experimentation and Further Development SER's development and production of dry reed switches has been supported by experiments carried out by several departments of L M Ericsson. To decide on the best heat treatment for the reed, measurements were made of the coercive force of the reed as function of furnace temperature and furnace time. Values were thus fixed which have since been used with good results. The quality of the contact plating has been studied in respect of thickness, uniformity, adhesion and cracking tendency. Spot checks are still made of the current production to ensure that the thickness of platings is within the tolerances which have been found to give the longest life: also that the number of cracks in the plating is not too great. L M Ericsson's Component Testing Department has made extensive tests on dry reed switches of SER and other makes. Operate and release ampere-turns have been measured as function of gap and overlap on adjustable models. Contact pressure and magnetic flux have also been tested on models. Operate and release times and contact bounce have been studied under different conditions. The perhaps most important tests were

131 N made in the Department's life test equipment for sealed contacts, in which the contacts performed make and break operations per second. The time before a contact failure occurred was generally - months. These tests admittedly take a long time to carry out, but they have proved of extreme value. They have provided information concerning the wear resistance of different contact materials, the effect of different gaps and overlaps on life expectancy, and concerning the life of SER switches compared with other makes. Typical data for SER dry reed switches are listed below. It soon became apparent that the predominating type of functional fault in dry reed switches is failure or great delay in the break function. When the limit for fault-free operation of the contact has been reached, these faults at first occur only occasionally and separated by a large number of correct contact operations. The faults fairly soon become more numerous, however, and after some time the unit ceases to function altogether. The reason for failure of the break function is the migration of material that occurs in the contact surfaces as a result of electric erosion in conjunction with the breaking of the current in the inductive circuit. The surfaces become deformed and tend to bind or stick together. The experiments on the dry reed switches were directed to discovering the most suitable means of electrical protection for the contacts ("spark quenching") and a contact material (surface coating) with little tendency to bind or stick. CR unit was found to offer suitable contact protection. number of metals and alloys were tried as contact materials in varying thickness of plating. The longest life was obtained with rhodium plating. Typical Data Operate time t 0. W energizing power t.0 W energizing power Contact bounce t W energizing power Release time. ms 0. ms 0.-. ms min. 0. ms Determined mainly by time constant of winding Max. operating frequency Number of fault-free operations 00 m contact current, 0 V, inductive load % of dry reed units 0 % of dry reed units 0 c/s > 0 f ' > 00-0«Magnetomotive force for operation 0-0 t Release occurs at - t Contact resistance New contacts fter 00 0 i; operations, median value Insulation resistance Breakdown voltage Q 0.0 Q 0 Q 00 V

132 Bibliography. ELLWOOD, W. B.: Glass Enclosed Reed Relay. Elect. Engng ():, pp HOVGRD, O. M. & PERREULT, G. E.: Development of Reed Switches and Relays. Bell Syst. tech. J. {\):, p. 0.. BNNOCHIE, J. G. & FURSEY, R.. E.: Sealed Contact Reed Relays.. T. E. J. Z():, pp... TEVONIN, R.: The Dry Reed Logic and Memory Unit. Western Electric Engr (0):, pp.. - Contact Capsules for Switching. Electronics.?_?(] 0): Sept. 0, pp... PEEK, R. L., JR: Magnetization and Pull Characteristics of Mating Magnetic Reeds. Trans mer. Inst. Elect. Engrs 0(): Sept., pp. 0.

133 'hjfcy&t NEWS/rom i \ / i ll Quarters of the World Empresa de Telefonos utomaticos de Quito recently signed a contract with L M Ericsson for the extension of its RM exchange and for the provision of subscriber-dialled long distance traffic via a radio link to the port of Guayaquil. similar agreement was made with Empresa de Telefonos utomaticos de Guayaquil (ETG). The picture shows a tour of the exchange building with (from left) Dr. Francisco costa Yepez, Ecuador's Eoreign Minister, Dr. Gonzalo Toro Teran, Under- Secretary of the Ministry of Public Works and Communications, and Sven Wenhammar, L M Ericsson representative, at the trunk switchboard. L M Ericsson Expands Irish Telephone Network L M Ericsson has received an order from the Irish P. & T. for a number of automatic telephone exchange equipments for extension of the Irish rural network. The value of the order is. million kronor. The first Ericsson exchange delivered to Ireland was opened at Limerick in. The automatization of urban and rural telephone traffic is proceeding at a rapid rate. Four city exchanges for a total of,000 subscribers are already in operation. Orders for Crossbar Lines Pass Three Million Mark New order for,000 lines from Helsinki L M Ericsson at present has orders from Ireland for telephone exchanges to a value of over million kronor, and for telex centres for some 00,000 kronor. These orders are of special interest since the Irish market has earlier been completely dominated by other telephone manufacturers. L M Ericsson recently received an order from the private Helsinki Telephone ssociation for automatic telephone switching equipment for over,000 lines. This equipment, of crossbar type, will be used chiefly for additions to a number of exchanges in Helsinki. The order also includes switching equipment for connection to exchanges in the outer area of Helsinki as well as a number of private branch exchanges. Ericsson contracts with Helsinki, covering equipment delivered and on order, now amount to some 00,000 local dial lines. With this new order from the Helsinki Telephone ssociation, L M Ericsson has passed the three million mark in crossbar lines delivered and on order for public automatic exchanges throughout the world. The first million was reached in, the second in 0. L M Ericsson has delivered a,000-line RF exchange to Hafnarfjordur, Iceland (below).

134 Telex Order from Canada n order has come in from Canadian Overseas Telecommunication Corp. for two automatic telex central equipments of Ericsson crossbar type for intercontinental telex service between Canada, Europe and ustralia. The equipments are to be installed at Montreal and Vancouver and will form a link in the British Commonwealth round-the-world project. Two automatic exchanges for intercontinental telephone calls were ordered from L M Ericsson earlier in the year. The order comprises an initial capacity of 00 circuits at Montreal and 00 at Vancouver. First Two Crossbar Exchanges Now Operating in New Zealand The first Ericsson crossbar exchanges in New Zealand are now in operation, Onerahi with,000 lines and Kensington with,00, Both exchanges are in the Whangarei district. In conjunction with their inaugu- ration the equipment was demonstrated to Postmaster-General. E. Kinsella. Mayor of Whangarei J. F. Johnson, Chief Postmaster C. E. Earle, and other visitors, by District Engineer K. Johnson (photo above). Swedish industry has formed an rgentine Foundation with the object of promoting Swedish-rgentinian relations. This is to take the form of seholarships or research grants to academicians, specialists and researchers from the rgentine and Sweden. The administration of the funds will he in the hands of the Swedish Institute. similar foundation has been created in the rgentine. One of the Swedish Hrms supporting the foundation is L M Ericsson. To spread knowledge of the purposes of the foundation, Dr. Roberto Noble, chief editor of Clarin, Buenos ires' largest newspaper, has been on a visit to Sweden. He is seen below (centre) at L M Ericsson's offices in Midsommarkransen. L M Ericsson's sales company in Ecuador, Telefonos Ericsson C.., Quito, has moved into new premises (above). Nevv President of North Electric William H. Graham has been appointed president of L M Ericsson's merican manufacturing company. North Electric Company, of Galion. Ohio. He succeeds William Tucker, who has retired from the post of chairman of the board and president of the company, in which Mr Graham has been executive vice president since.

135 The Bishop of Stockholm, Helge Ljungberg, on a visit to the Midsommarkransen factory. He is seen above with Messrs. Nils Skoldberg and Malte Patricks. The Nigerian Minister of Information, T.O.S. Benson, has been on an unofficial visit to Sweden. In the photograph above, taken at Midsommarkransen, he is inspecting the Ericsson telephone. On his right is his secretary, J.. Otoki. trade delegation from Cameroon has been to Midsommarkransen. (bove) The Cameroon Minister of Finance, Victor Kanga, signs his name in the visitors' book. The Ericofon had a prominent place at the Fifth International Food Congress and Exhibit in New York. The Kellogg Company used nine Ericofons to bid the more than 0,000 visitors good morning in twelve languages. The Stockholm Technical Fair had its premiere this year. The Ericsson Swedish Sales Company exhibited components chiefly from the head company, B Svenska Elektronror and B lpha.

136 new,000-line dial exchange, type GF, was officially opened at Colon, Panama, in July. The first call over the new exchange was put through by the President of the Republic, Roberto F. Chiari. The photograph shows (from left) Vice President J. D. Bazan, President Chiari, Mr. T. E. Oglesby. president of Cia Panamena de Fuerza y Luz, Mr. Hoagland, Mr. C. Levy Salceder, and Bishop Serrano of Colon. L M Ericsson in Swedish Industrial Group for Space Developments Continued Finnish utomatization with Ericsson Crossbar L M Ericsson has received an additional large order for nine automatic telephone exchanges as part of the project of conversion of the Finnish network to nationwide subscriber-to-subscriber dialling. The exchanges will have crossbar trunk switching equipment. They are part of the fifth stage of the conversion plan, the whole of which is expected to be completed during the '0's. The first automatic long distance exchanges were opened in at Tampere, Toijala, Lahtis and Hameenlinna. The Helsinki area was linked to this automatic network in. Finnish national and international trunk exchanges delivered and on order from L M Ericsson represent a value of over 0 million kronor. Swedish industrial group for space developments has been formed in Stockholm, with representatives from L M Ericsson, SB, Svenska Flygmotor, G, SE and Bofors. The group operates as a section of the Federation of Swedish Mechanical Engineering Industries, and its function is to study peaceful uses of space technology and to watch over the interests of Swedish industry on the growing space equipment market, especially with a view to extended European cooperation in this field. The group will also, if required, act as advisory committee to the government on questions of space technology. The formation of the group follows on the government's decision to propose to parliament that Sweden be represented on the European Space Research Organization, ESRO, which at present includes twelve nations. The plans for ESRO call for a joint contribution of. billion kr. during ten years. Sweden's share will be million. Plans exist for the launching of high altitude rockets, some 0 earth satellites, four space observatories and two moon satellites. The base, at least for most of the experiments with high altitude rockets, is to be a vast area around the town of Kiruna in north Sweden. The cost of the base is preliminarily estimated at 0 million kr. satellite observation station costing million kr. may also be built. The base is to be manned by some 0 researchers and technicians. new,000-line RF exchange has been opened at Yala, Thailand. The opening ceremony included the blessing of the new exchange by a number of monks. 0

137 UDC.. LME ERIKSEN, E J: ie Development and Future of Wide Band Carrier Systems. Ericsson Rev. ():, pp The use of wide band carrier systems on different transmission media such as symmetrical pair cables, open-wire lines, coaxial cables and waveguides is dealt with in this article with special reference to circuit capacity and future development. The article, whose emphasis is on the coaxial cable h.f. line, is based on an address given before the Swedish ssociation of Electrical Engineers, held on March. ) s: a Co fs < ~ * <U C > N 'C ;S at s o -a d So!" sal Pi K-s idead fact th reliab ti is a The and g«j* *" "S «P (-. *J eft dry stigh s en u _ 0 s *e en CJ ai I g* P u o o 0 c >>*i u -d oil c 0,0 d J- -whi jp UJO c " E ti "d w c;u 0 u -d a >> 0 *j d C ent <G :0 M etc S I ~ <-> M c X u u. S a o g J c a» 0 *. r-» U ft d > c oa» <» CO d w W o o B oc.a as: '% "H.S-: a UDC.. LME 0 RPP, Y: Planning of Multi-Exchange Networks with id of a Computer. III. Planning of Junction Circuits in Multi-Exchange Networks. Some Fundamental Principles. Ericsson Rev. ():, pp Methods aimed at simplifying the estimate of the future volume of traffic between exchanges in a multi-exchange area after modification of the network structure were presented in Ericsson Technics No.,. In Ericsson Technics No.,, it was shown how the number and locations of the exchanges, and the boundaries between them, can be determined by starting from a subscriber inventory. condensed account of these two papers was given in Ericsson Review No.,. This article follows on the previous publications and gives a preliminary survey of two of the fundamental principles which can be employed when planning junction circuits. This will be followed by more extensive accounts at a later date. UDC.. LME 0 RPP, Y & OLLUS, Y: Practical pplication of the Planning of Multi- Exchange Networks with id of a Computer. Exchange Locations and Boundaries. Ericsson Rev. ():, pp. 0. The method of planning a telecommunications network described in Ericsson Review No.,, has been employed in drawing up the general plan for extension of several existing networks, one of which was the bo network in Finland. This article, which presents a resume of the bo plan, illustrates the practical use of the method.

138 The Ericsson Group ssociated and co-operating enterprises E U R O P E Denmark L M Ericsson /S Kebenhavn F, Finsensvej, tel: Fa, tgm: eriesson Telefon Fabrik utomatic /S Kmbenhavn K, maliegade, tel: C, tgm: automatic Dansk Signal Industri /S Ktbenhavn F, Finsensvej, tel: Fa, tgm: signaler Finland O/Y L M Ericsson /B Helsinki, Fabianinkatu, tel:, tgm: ericssons Great Britain Swedish Ericsson Company Ltd. Sweden London, W. C., High Holborn, tel: Holborn 0, tgm: Telefonaktiebolaget L M Ericsson Stockholm, tel: 00 00, tgm: teleric telefonbolaget Production Control (Ericsson) Ltd. London, W. C. f, High B lpha Sundbyberg, tel:00, Holborn, tel: Holborn 0, tgm: aktiealpha-stockholm tgm: productrol holb Italy SETEMER, Soc. per z. Roma, Via G. Paisiello. tel:..., tgm: setemer SIELTE, Soc. per z. Roma. C. P. 0 ppio, tel: 0, tgm: sielte FTME, Soc. per z. Roma, C.P. 0 ppio, tel: 00, tgm: fatme Netherlands Ericsson Telefoon-Maatschappij, N.V. Rijen (N.Br.), tel: 0-, tgm: erictel den Haag Schevem'ngen, 0, Palacestraat, tel: 00, tgm: erictel-haag Norway /S Elektrisk Bureau Oslo NV, P.B. 0, tel: Centralbord 0, tgm: elektnken /S Industrikontroll Oslo, Teatergaten,tel: Centralbord 0, tgm: indtroll /S Norsk Kabelfabrik Drammen, P. B. 0, lei:. tgm: kabel /S Norsk Signalindustri Oslot Bygda alle", tel: Centralbord, tgm: signalindustri France Societe des Telephones Ericsson Portugal Colombes (Seine), Boulevard de la Sociedade Ericsson de Portugal, Finlande.tel: CH rlebourg -00. Lda. Lisboa,, Rua Filipe Folque, tgm: eriesson tel:, tgm: eriesson Paris e, Rue de Courcelles, tel: CRnot -0. tgm: eric Spain teliers Vaucanson, Pons XX. B. Cia Espanola Ericsson, S.. P..0.tel: MENilmontant --0, Madrid, Torre de Madrid er tgm: atelcanson piso, oficina, Plaza de Espana, tel : 00, tgm : eriesson gencies E U R O P E Belgium Electricity et Mcanique Suedoises Bruxelles, Rue de Stassart, tel:, tgm: electrosuede Greece "ETEP" S.. Commerciale & Technique thens, Lycavettus Street, tel: 0, tgm: aeter-athinai Iceland Johan Ronning H/F Reykjavik, P. O. B., tel: 0, tgm: ronning Ireland Communication Systems Ltd. Dub/in, Pembroke Road, Ballsbridge. tel: 0 tgm: crossbar S I. Burma Burma siatic Co. Ltd.. Ericsson Departmentftongoon, P.O.B.00, tel: 0, tgm: eriesson Cambodia The East siatic Company Ltd. Phnom-penh, P.O.B.. tel: -00-0, tgm: pyramide Ceylon Vulcan Trading Co. (Private) Ltd. Colombo, New Caffoor Building, 0, Church Street, tel: -,tgm: vultra China The Ekman Foreign gencies Ltd. Shanghai, P. O. B., tel: -, tgm: ekmans Cyprus Zeno D. Pierides Lamaca, P.O.B., tel: 0, tgm: pierides B Ermex So/no, tel: 000, tgm: elock-stockholm B Ermi, Karlskrona, tel: 00, tgm: ermibolag-karlskrona B Rifa Bromma, tel: 0, tgm: elrifa-stockholm B Svenska Elektronror Sfockholm 0, tel: 0 0, tgm: electronics L M Ericssons Driftkontrollaktiebolag Solna, tel:, tgm: powers-stockholm L M Ericssons Signalaktiebolag Stockholm Sv, tel: 0 00, tgm: signalbolaget Iran Ira no Swedish Company B, Teheran, Khiabane Sevom Esfand, tel:, tgm; iranoswede Iraq Usam Sharif Company W.L.L. Baghdad, Sinak-Rashid Street, tel: 0, tgm: alhamra Japan Gadelius & Co. Ltd. Tokyo C, P. O. B., tel: 0-, tgm: goticus Jordan The rab Trading & Development Co., Ltd. mman, P. O. B., tel:, tgm: aradeve Korea Gadelius & Co. Ltd. Seoul, I. P. O. Box, tel:, tgm: gadeliusco Yugoslavia Merkantile Inozemna Zastupstva Zagreb, PoSt pretinac, tel:, tgm: merkantile, telex: Kuwait 0- Latiff Supplies Ltd. Kuwait, P. O.B., tel: 0, tgm: latisup L M Ericssons Svenska Forsdljningsaktiebolag Stockholm, Box. tel: 00, tgm: ellem Mexikanska Telefonaktiebolaget Ericsson Stockholm, tel: 0000, tgm: mexikan Sieverts Kabelverk B Sundbyberg, tel: 0, tgm: sievertsfabrik-stockholm Svenska Radioaktiebolaget Stockholm, lstromergatan, tel: 0, tgm: svenskradio B Ostmarks Ldsfabrik Eskitstuna, Munktellsgatan, tel: Switzerland Ericsson Telephone Sales Corp. B, Stockholm, Zweigniederlassung Zurich Zurich, Postfach ZUrich. tel:, tgm: telericsson West Germany Ericsson Verkaufsgesellschaft m. b. H. Dusseldorf, Postfach, tel:, tgm: erictel India SI Ericsson Telephone Sales Corporation B New Delhi, P.O.B., reg.mail: / saf M Road (Delhi Estate Building),tel:, tgm: inderic Calcutta, P. O. B.. tel: -, tgm: inderic Indonesia Ericsson Telephone Sales Corporation B Bandung, Djalan Dago, tel:, tgm: javeric Djakarta, Djalan Gunung Sahari, tel: Kota, tgm: javeric Lebanon Telefonaktiebolaget L M Ericsson, Technical Office Beyrouth, Rue du Parlement, tmmeuble Bisharat, tel:, tgm: ellem Turkey Ericsson Turk Ticaret Ltd. $irketi nkara, dil Han, Zafer Meydani, Yenisehir, tel: 0, tgm: ellem Istanbul, Istanbul BUrosu, Liman Han. Kat, No., Bahcekapi, tel: 0. tgm: ellemist Hong Kong Syria The Swedish Trading Co. Ltd. Georgiades, Moussa & Cie Da' Hongkong, P. O. B. 0, tel: mas. Rue Ghassan, Harika, tel: -, tgm; swedetrade -0-, tgm: georgiades Lebanon Swedish Levant Trading (Elie B. Helou) Beyrouth, P. O. B., tel:, tgm: skefko Pakistan Vulcan Industries Ltd. Karachi City, P. O. B., tel: 0, tgm: vulcan Philippines U.S. Industries Philippines Inc. Manila P. R., P. O. B., tel: --, tgm: usiphil Saudi rabia Mohamed Fazil bdulla rab Jeddah, P. O. B., tel: 0, fgm: arab Singapore and Malaya The Swedish Trading Co. Ltd. Singapore, Chartered Bank Chambers, Battery Road, tel:, tgm: swedetrade Thailand Ericsson gency Office, Telephone Organization of Thailand Bangkok, Ploenchitr Road, tel:, tgm: telthai Vietnam Vo Tuyen Dien-Thoai Viet-Nam, Saigon, Dai-lo Thong-Nhut, tel: 00, tgm: telerad Ethiopia F R I C Swedish Ethiopian Company dd.s baba, P. O. B., tel:, tgm: etiocomp Ghana The Standard Electric Company ccrd, P.O.B., tel:, tgm: standard Kenya, Tanganyika, Uganda, Zanzibar Transcandia Ltd. Nairobi, Kenya, P. O. B.. tel:. tgm: transcanda Liberia Swedish gencies Liberia Co. Monrovia, P.O.B. 0, tel:, tgm: salco (Except sales to public institutions) Libya The Gulf Trading Co. Tripoli, P.O.B., tel:, tgm: gultraco Mauritius Mauritius Trading Co. Ltd. Port Louis, P.O.B. 0, tgm:agentou Morocco Elmar S.. SEYRE Tangier, Francisco Vitoria,, tel: -0, tgm: elmar Egypt, Telefonaktiebolaget LM Ericsson, Egypt Branch Cairo, P. O. B. 0, tel:, tgm: elleme Northern and Southern Rhodesia, Nyasaland LM EricssonTelephoneCo. (Pty.) Ltd. (Branch Office of LM Ericsson Telephone Co. Pty. Ltd. in Johannesburg) Salisbury, Southern Rhodesia, P.O.B., tel: 0 0, tgm: eriesson South frica, South-West frica L M Ericsson Telephone Co. Pfy. Ltd. Johannesburg, Transvaal, P. O. B. 0, tel: -, tgm: ericofon Tunisia Telefonaktiebolaget LM Ericsson, Technical Office Tunis, Boite Postale 0. tel: 00, tgm:ericsson M E R I C rgentine Cla Ericsson S.. C. I. Buenos ires, Casilla de correo 0,tel: 0, tgm: eriesson Cla rgentina de TeleTonos S.. Buenos ires, Peru, tel: 0 0, tgm: catel Cla Entrerriana de TeleTonos S.. Buenos ires, Peru, tel: 0 0, tgm: catel Industrias Eldctricas de Quilmes S.. Quilmes FNGR, de Octubre 00, tel: 0-, tgm: indelqui-quilmes Brazil Ericsson do Brasil ComeVcio e Industria S.. Rio de Janeiro, C. P. 0, tel: -00, tgm: eriesson Canada LM Ericsson Ltd. Montreal, P.Q., 00 Laurentian Boulevard, City of St. Laurent, tel: 0, tgm: caneric Toronto. On/., P. O. B., tel: BE -0 Chile Cla Ericsson de Chile, S.. Santiago, Casilla 0, tel:, tgm: ericsson-santiagodechile Mozambique tgm: eriesson par. -00, Ecuador Telefonos Ericsson C.. Quit* Cos.Ma, tel: 00. tgm: eriesson Guayaquil, Casilla, tel: tgm: eriesson Mexico Telefonos Ericsson S.. Mitia D.F., partado, tel: -0 tgm: coeric Industria de Telecomunicacin S.. de C.V. Mexico, D.F., Londres No., tel: S00, tgm: industel Peru Cia Ericsson S.. Lima, partado, tel:, tgm:,ricss0 Soc. Telefnica del Peru, S.. requipa, partado, tel: 00, tgm: telefonica Uruguay Cla Ericsson S.. Montevideo, Casilla de Correo, tel: --, tgm: eriesson US The Ericsson Corporation New York, N. Y., 00 Park venue, tel: Murray Hill -00, tgm: erictel North Electric Co. Gal/on, Ohio P. O. B., tel: Howard -0] tgm: northphone-galionohio Venezuela Cla nnima Ericsson Caracas partado, tel:, tgm: eriesson TeleTonos Ericsson C.. Caracas, partado, tel:, tgm: tevela USTRLI & OCENI. ustralia L M Ericsson Pty. Ltd. Melbourne C (Victoria), 0 Collins Street, tel;, tgm: ericmel North Sydney (NSW), Blue's Point Road, tel:, tgm; ericsyd Teleric Pty. Ltd. Me/bourne C (Victoria), 0 Collins Street, tel:, tgm; teleric North Sydney (NSW), Blue's Point Road, tel:, tgm: teleric Nicaragua J. Martins Marques Lourenco Edmundo Tefel Managua, D.N.,j lorques, P. O. B., tel:, partado Postal, tel: 0, tgm: tinsmarques tgm: edfelco Nigeria I.P.T.C. (West frica) Ltd. Lagos, Panama Productos Mundiales, S.. Pol?:?;?;, 0,,el:, tgm: nawv'^ T.~S S. in^fl consult -0, tgm: mundi and Machinery Co. Ltd. Kha, Sudan TECOM Technical Consulting Paraguay S.. Comercial e Industrial H. toum, P.O.B., tel:, ext.?e.\ e "Vl sunudn, Cas.lla,, tgm: sutecoma tel:, tgm: pargtrade Bolivia M E R I C Johansson & Cia, S.. La Paz, Casilla, tel: 00, tgm: Johansson Curacao N. W. I. S. E. L. Maduro & Sons, Inc. Curacao, P. O. B., tel: 00, tgm: madurosons-wiltemstad Dominican Republic Garcia & Gautier, C. por. Santo Domingo, partado, tel:, tgm: gartier Guatemala Nils Pira Ciudad de Guatemala, partado, tel:, tgm: nilspira-guatemala Honduras Quinchn Len y Cla Tegucigalpa, partado, tel:, tgm: quinchon Jama Morri=, t- Puerto Rico Splendid Inc. San Juan, P. 0. B., tel: -0, tgm: splendid El Salvador Costa Rica Surinam Dada-Dada & Co. San Salvador, partado, tel: 0, tgm; dada Tropical Commission Co. Ltd. Son C. Kersten & Co. N. V. Po«' Jos, partado, tel:, maribo, P. O. B. 0, tel:, tgm: troco tgm: kersten Trinidad, W. I. Leon J che Ltd. Por.-of-Spoi", 00 Frederick Street, tel:, tgm: achegram US Clark Walter Corporation Newark, N. J., Broad Street, tel: Mitchell -, tgm: wirewalter-newarknj. (For intercom) State Labs. Inc. New York, N. U Park venue South, tel: Oregon -00, tgm: statelabs (For electron tubes) USTRL! & OCENI* New Zealand I: