Technical Document TNA 117: Telecom 2048 Kbit/s. Standard Network. Interface

Transcription

1 Technical Document TNA 117: 1992 Telecom 2048 Kbit/s Standard Network Interface Access Standards Telecom Corporation of New Zealand Limited Wellington New Zealand Issue 1: May 1992 ORIGINAL A5 TEXT RE-FORMATTED TO.PDF, November Up-dated to incorporate amendment No. 1

2 2 Telecom New Zealand Limited

3 1 CONTENTS Section Page RELATED DOCUMENTS 2 FOREWORD 5 1. SCOPE 7 2. GENERAL DEFINITIONS PHYSICAL REQUIREMENTS ELECTRICAL REQUIREMENTS FRAME STRUCTURE 22 FIGURES FIG. 1 FIG. 2 FIG. 3 FIG. 4 SCREEN CONDUCTOR EARTHING MASK OF PULSE AT 2048 KBIT/S INTERFACE JITTER & WANDER TOLERANCE AT 2048 KBIT/S TYPICAL EXAMPLES OF CRC PROCESSING APPENDICES APPENDIX NO. 1 SUMMARY OF COMPLIANCE REQUIREMENTS 1

4 2 RELATED TELECOM DOCUMENTS PTC 100 PTC 101 PTC 107 PTC 109 Permit to Connect : General Conditions Electrical Safety Requirements for a Telecom Permit to Connect PABX: External Port Interface Conditions PABX: Transmission Requirements PTC 132 Telecom ISDN: Primary Rate User-Network Interface, Layer 1 PTC 207 PTC 217 PTC 232* PTC 301 TNA 118 TNA 151 General Requirements for PABX Equipment Requirements for Bandwidth Management Systems Requirements for ISDN Terminal Equipment: Primary Rate Access Telephone Network Interconnection Direct Dial In Services Telecom Telephone Network Transmission Plan * To be published later REFERENCE DOCUMENTS CCITT Blue Book, Fascicle III.4 and III.5 Recommendations (G. Series) CCITT G Series Recommendations ( published after release of Blue Book) Oftel Code of Practice for the Design of Private Telecommunications Networks: Issue 1, November 1990 AUSTEL Private Network Design Guide PNDG AUSTEL Technical Specification TS : General Requirements for Customer Equipment Connected to a 2048 kbit/s Telecomms Service (including Amendment No 1/1991) Telecom Corporation of New Zealand Limited Standard Terms and Conditions for Telecom Network Service to Non-Residential Customers 2

5 3 TELECOM DISCLAIMER Telecom makes no representation or warranty, express or implied, with respect to the sufficiency, accuracy, or utility of any information or opinion contained in this Technical Document. Telecom expressly advises that any use of or reliance on such information is at the risk of the supplier. Telecom shall not be liable for any damage or injury incurred by any person or organisation arising out of the sufficiency, accuracy, or utility of any such information or opinion. Telecom has provided this information to assist suppliers and will expect the basic operations of any device, to which this Technical Document applies, to be tested to ensure that the product does operate as claimed by the manufacturer. The grant of a Telepermit for a device in no way indicates Telecom acceptance of responsibility for the correct operation of that device under all operating conditions. Additionally, Telepermits granted individually for separate products in no way guarantee the satisfactory operation of two or more of such products when connected together. 3

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7 5 FOREWORD This Technical Document has been prepared by Telecom as a standard for any customer premises equipment having 2048 kbit/s interfaces intended for connection to the Telecom network. This Technical Document complies with those requirements of CCITT Recommendation G. 703 that apply to 2048 kbit/s digital interfaces. Under the Telepermit system, a separate Specification in the "PTC 200" series will be used to cover the particular type of equipment concerned. Such specifications will call up this Document as necessary where a 2048 kbit/s interface is involved. Specific examples are Specifications PTC 207 covering PABX's, PTC 217 covering Bandwidth Management Systems (BMS), and, for the future, PTC 232 covering ISDN Primary Rate Access. This Technical Document describes the physical and electrical interface requirements for interconnection with the Telecom network by other organisations. It applies to leased circuits, PABX's, bandwidth management systems, etc., as appropriate. It is complementary to the particular specification for the equipment concerned, and any other technical specifications that may apply. As with Specifications PTC 207 and PTC 217, it is not proposed that the requirements of this Technical Document will, in general, be tested by specifically accredited test laboratories in New Zealand. Assessment is normally based on manufacturer's selfcertification by means of a clause-by-clause compliance statement, with results of manufacturer's testing where specified. However, this does not preclude the possibility of testing by accredited test laboratories in New Zealand. Also, test results from overseas test laboratories against equivalent standards will generally be accepted (e.g. AUSTEL TS 016). General requirements and other technical matters relating specifically to the interconnection of networks are covered in a separate 'family' of PTC Specifications numbered in the "300" series. 5

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9 7 1 SCOPE 1.1 Equipment covered (1) This Technical Document describes the Layer kbit/s interface requirements for customer premises equipment intended for connection to the Telecom Network. (2) As with other Specifications and Documents in the PTC and TNA series, an effort is also made to explain the significance behind the various requirements. 1.2 Compliance (1) Compliance with the general requirements of Specification PTC 100, and the electrical safety requirements of PTC 101 where applicable, shall be regarded as an essential prerequisite for the granting of a Telepermit. In addition, compliance with the requirements of the appropriate PTC 200 series Specifications shall be required. (2) Such PTC 200 series Specifications will call up this Technical Document where necessary to ensure compliance with requirements for 2048 kbit/s interfaces. 1.3 Related Specifications and Technical Documents References are made to PTC Specifications and other TNA Documents covering other associated technical requirements. These are listed near the front of this Technical Document on page 2, together with other reference documents. 1.4 Application of Telepermit (1) As stated in the "Standard Terms and Conditions for Telecom Network Service to Non-Residential Customers", and also in Specification PTC 100, only that equipment granted a Telepermit and bearing a label to that effect may be connected, either directly or indirectly, to the Telecom network. (2) Similar principles apply to network interconnection, and private network equipment may well include equipment covered by this Technical Document. Telecom requires assurance that such equipment is compatible with the Telecom network and not likely to either disrupt or degrade service to Telecom customers, or create any hazardous conditions within the Telecom network. Similarly, other equipment suppliers will generally require some assurance that connecting equipment is compatible with their interface specifications. This is a matter for negotiation between the suppliers concerned. (3) Telepermits are not issued solely under this Technical Document as it deals with a particular type of interface and not to a functional item of equipment. Full details of the relevant Telepermit requirements and conditions are given in the PTC 200 series Specification applicable to the equipment concerned. 7

10 8 1.5 Responsibilities under the Telepermit system Telepermit Applicant (1) Suppliers of telecommunications equipment have certain responsibilities to their customers. Primarily, such suppliers should ensure that the overall performance resulting from use of their equipment is satisfactory when used in a private network connected to the Telecom network. Customers' perception of the performance of any network is dependent on the satisfactory performance of all individual network components working in combination. Compliance with CCITT Recommendations in all respects is the most effective way of achieving satisfactory performance. All PTC Specifications and TNA Documents are based primarily on satisfying CCITT requirements. (2) Customers' equipment designed for connection to Telecom 2048 kbit/s interfaces will be covered by a separate PTC Specification, with reference to this Specification where appropriate. Telepermit applications for such equipment will normally involve submission of a clause-by-clause compliance statement, followed by a Limited Permit trial (ref. Specifications PTC 207, PTC 217, etc.). The compliance statement shall include reference to the clauses of this Technical Document, together with manufacturer's test results as necessary. (3) Further details of Telepermit applicants' responsibilities are covered in the appropriate PTC specification covering the equipment concerned Telecom responsibility (1) Telecom's primary responsibilty in setting up the Telepermit system is to define interfaces and set reasonable and practicable access standards for the direct or indirect interconnection of privately-supplied equipment with its network. The standards set are the minimum necessary for equipment to be acceptable for connection. Under the Telepermit system Telecom does not set standards for optimal performance of equipment connected to its network. Similarly, Telecom cannot ensure that products connected will work under all operating conditions. (2) The primary aims of the Telepermit system are to ensure safety and avoid degradation of the network and its services due to the connection of unsuitable terminal and private network equipment. PTC Specifications and TNA Documents, which include Codes of Practice, are examples of the approach being taken by Telecom to advise customers and industry on suitable practices and standards of performance required to minimise unnecessary service problems. Any Telecommunications network comprises a variety of component devices from different sources. To ensure satisfactory performance across the network, it is important that established standards are used wherever possible. Suitable recommendations are made where there is any possibility of alternative standards being used. This includes maintenance and fault clearance practices to be used. Recommendations will be given, especially where two or more separate parties are involved and there are difficulties in defining responsibilities clearing faults. 8

11 9 (3) Telecom's general intention is to avoid, as far as possible, involvement in routine Telepermit testing functions. Nevertheless, Telecom may assist suppliers in some circumstances. In line with the conditions laid down in Specification PTC 100, Telecom prefers to base the granting of Telepermits on testing carried out by independent testing laboratories wherever possible. (4) It is recognised that some equipment is highly complex, such as PABX's and BMS equipment, and that laboratory testing is unlikely to duplicate all conditions likely to be experienced in the field. As a result, Telecom generally accepts the principle of selfcertification by manufacturers for such equipment. 1.6 Harmonisation with overseas standards (1) The requirements of this Technical Document are primarily based on CCITT Recommendations but Telecom has also endeavoured to harmonise with other overseas standards wherever there is no direct conflict with established Telecom practices. (2) In particular, the requirements of this Technical Document have been aligned with those of British Standards and the Office of Telecommunications (Oftel) in the U.K., and with Technical Standards produced by the Australian Telecommunications Authority (AUSTEL), wherever possible. 1.7 Non-compliance aspects (1) When preparing an application for a Telepermit, it may be apparent that some technical aspects are not fully compliant with the requirements of this Technical Document. Such non-compliance aspects shall be clearly indicated in the Testing Authority's or Manufacturer's Test Results. If critical information has been omitted and service problems result during a Limited Permit trial, it is unlikely that the Telepermit will be granted. If such omissions come to light after a Telepermit has been granted, and are the cause of service problems, that Telepermit is liable to cancellation. (2) Every non-compliant aspect must be fully addressed by the applicant and, where necessary, discussed with the manufacturer. The Telepermit application shall then incorporate either:- (a) evidence that the product has been suitably modified to fully comply with this Technical Documnent, or (b) an explanation of, and justification for non-compliance, together with the applicant's intentions regarding use of the product by customers. 9

12 10 2 GENERAL 2.1 Mode of presentation Those aspects of this Technical Document which are regarded as mandatory are printed in plain type with each paragraph formally numbered. Comments, recommendations and explanations, which are added only as indications of the means of compliance, are shown in italics. Smaller type is used and each paragraph is preceded with a " " symbol instead of a clause number. 2.2 Test procedures (1) Normally, equipment covered by this Technical Document will be subject to a Limited Permit Trial such as those described in Specification PTC 207 or PTC 217. (2) For the purposes of a Limited Permit Trial, test results for requirements of this Technical Document may be those produced by the manufacturer, by another Telecommunications Authority, or by a laboratory recognised for this class of testing. Such test results must be formatted to this Technical Document for them to be considered for the grant of a Telepermit. In general, a compliance statement alone is not sufficient for acceptance. For equipment covered by this Technical Document (apart from electrical safety requirements), test results will be accepted from manufacturer's test laboratories. Alternatively, test results will be accepted from laboratories approved by overseas authorities such as BABT, Austel, etc in addition to those formally accredited in New Zealand. 2.3 Digital signalling Details of digital signalling are not regarded as part of the Layer 1 requirements for a digital interface and therefore have not been included in this Document. Details of signalling requirements for 2048 kbit/s interfaces are incorporated separately in the relevant PTC Specification or TNA Document. 2.4 Electrical safety (1) All equipment shall comply with the general electrical safety requirements of Telecom Specification PTC 101, as described in the particular product Specification. Compliance testing to Specification PTC 101, Part C, may only be undertaken by one of the following:- (a) a Telarc registered laboratory, (b) a Laboratory which has been accredited by a Telarc affiliated laboratory registration authority, or, (c) a laboratory recognised by the New Zealand Ministry of Commerce, Energy and Resource Division, and listed in ECP 3. 10

13 11 (2) For equipment requiring an earth connection for correct operation, the requirements of Specification PTC 101, clause B 3.3 shall be complied with. 11

14 12 3 DEFINITIONS 3.1 Approach used (1) In general, definitions set by the International Consultative Committee on Telegraph and Telephone (CCITT) apply throughout this Technical Document. Nevertheless, some terms are not defined by CCITT. In addition, other terms are used in different ways in different countries. (2) Further general definitions that may apply to equipment covered by this Technical Document are given in Specifications PTC 100, 217 and also in Technical Document TNA 110. (3) To avoid potential confusion, the CCITT definitions are supplemented by the following definitions and by explanatory paragraphs which elaborate on the formal wording. Some of the equivalent names used overseas are provided in these explanatory paragraphs for the assistance of potential operators in the New Zealand market. Alternate mark inversion code (AMI code): is a line code that employs a ternary signal to convey binary digits, in which successive binary 1's are represented by signal elements that are normally of alternating positive and negative polarity but equal in amplitude, and in which binary 0's are represented by signal elements of zero amplitude. Ref. CCITT Blue Book, Recommendation G See also "bipolar violation". Applicant: is any person, or company, making formal application for a Telepermit for customer premises equipment intended for connection to the Telecom network. In practice an 'Applicant' may be a manufacturer (domiciled in New Zealand), an equipment importer, an installation agency (supplier),or even a Telecom customer. See clause 1.5 and also definitions given in Specification PTC 100. Bandwidth management system (BMS): is the general term describing any equipment which assembles into, or divides from a common transmission channel, a number of discrete lower order channels. See Specification PTC 217. Bipolar (or AMI) violation: is a binary 1 signal element which, in an AMI signal, is represented by an element which has the same polarity as the previous 1 signal element. Ref. CCITT Blue Book, Recommendation G Bit error rate (BER): is the ratio of the number of bit errors to the total number of bits in a digital signal transmitted in a given time interval. 12

15 13 Compliance statement: is a written submission supplied by a Telepermit (or Limited Permit) Applicant which addresses, clause by clause, the particular PTC or TNA Specification(s) applicable to the equipment in question. Cyclic redundancy check (CRC): is the monitoring of a digital bit stream to detect deviations from the expected bit patterns. The particular procedure for monitoring 2048 kbit/s digital streams is known as CRC-4 and is described in CCITT Recommendation G. 704, Clause DDI (direct dialling-in): is the facility to allow incoming calls from the PSTN to be switched directly to a specified station (e.g. PABX extension) without operator assistance. Also known as "Direct in-dial", or "DID" overseas. See Technical Document TNA 118. Digital circuit: is a circuit transmitting signals in digital form in both directions between a terminal device and a switching point, or between two switching points, and is the combination of two unidirectional digital channels. A digital channel is defined by the CCITT Blue Book, Fascicle I.3, as a one-way 64 kb/s digital path. Thus two such channels are required for two-way communication. Digital (line) link: is a means of digital transmission between two points comprising a digital line section, or a number of digital line sections connected in tandem. Digital line section: is a digital section implemented on a single type of transmission medium, such as symmetric copper pairs, optical fibre, etc. A digital line section includes line terminating equipment but not multiplexers. Reference CCITT Blue Book, Recommendation G. 701, Fig. 1. Digital trunk interface (DTI): an exchange interface for a 2048 kbit/s A-Law digital system having the characteristics of an "Interface A" as defined in CCITT Blue Book, Recommendation Q. 511, clause 3.1. Reference also CCITT Blue Book, Recommendations G. 703, G. 704 and G Encoding laws (A-law or µ-law): are two alternative methods of encoding samples of analogue signals into a binary form for pulse code modulation. Telecom has adopted A-law as its standard (ref. CCITT Blue Book, Rec. G. 711). Frame: in relation to digital signals, is either a consecutive set, or a cyclic set of time slots, where each individual slot can be identified by reference to a frame alignment signal. 13

16 14 Insertion loss: is the difference between the power delivered from a source directly to a load, and the power delivered to the same load from the same source but with the circuit under test connected between them, as shown in the expression:- Insertion loss = 10 log 10 P 1/P 2 db where P 1 = power delivered directly from source to load and P 2 = power delivered to the load with the test circuit inserted. Integrated services digital network (ISDN): is an integrated digital network in which the same digital switches and digital paths are used to establish connections for different services (e.g. telephony, data). Reference Specifications PTC , and TNA for further information on ISDN. Jitter: is the short term variation of the significant instants of a digital signal from their ideal position in time. See also "wander". Reference CCITT Blue Book, Recommendation G Limited Permit: is the formal term used by Telecom when granting permission to connect a limited number of installations to the Telecom network on a trial basis for a limited period. Such installations are normally of more complex equipment not fully tested locally. A Limited Permit trial is normally followed by the grant of a full Telepermit if the trial is satisfactory to the customer and presents no problems to the Telecom network. See also Specifications PTC 207 (PABX's) and PTC 217 (BMS equipment). Manufacturer: is the company responsible for the design and assembly of the equipment covered by this Specification. In most cases the manufacturer of equipment covered by this Technical Document is domiciled overseas and therefore requires an agent resident in New Zealand for the purposes of obtaining a Telepermit. The agent may be a susidiary of the parent overseas company or a separate company altogether. In turn, the agent may in some cases be the supplier of the equipment in question to the customer. Multiplex: equipment which assembles into, or divides from a common aggregate transmission channel, a number of discrete lower order tributary channels of fixed capacity and number. The term incorporates multiplexing (assembling) and demultiplexing (dividing) processes at the same location, thus involving both directions of transmission. 14

17 15 PABX network: is a combination of two or more PABX's directly linked for communication purposes by one or more lines. Power feeding: is the process of supplying power from one station to another via the transmission system bearer cable. Some power feeding arrangements use the transmission system bearer while others use separate copper pairs in the bearer cable. ppm: represents "parts per million". Pulse code modulation (PCM): is a process in which a signal is regularly sampled, each sample is quantized independently of other samples and the quantized value is encoded into a digital signal. Reference CCITT Blue Book, Recommendation G Return loss: is a quantity associated with the degree of match between two impedances Z 1 and Z 2 given by the expression:- Return loss (L R ) = 20 log 10 (Z 1 + Z 2 ) / (Z 1 - Z 2 ) db It follows that, if Z 1 and/or Z 2 are complex impedances, then the return loss derived by this formula will vary with frequency. Telecom network: is any or all of the telecommunications networks or links, including the actual line or circuit to which equipment is to be connected, that are provided by Telecom corporation of New Zealand Ltd for public or private use. Trunk: is any circuit (digital or analogue) between a PABX and a central office (local exchange) in the Telecom PSTN. Wander: is the long term variation of the significant instants of a digital signal from their ideal position in time. See also "jitter". Reference CCITT Blue Book, Recommendation G

18 16 4 PHYSICAL REQUIREMENTS 4.1 General characteristics (1) The Telecom standard 2048 kbit/s interface consists of a symmetrical screened pair with a characteristic impedance of 120? resistive. This is the preferred interface for connection to the Telecom network. (2) However, since the earlier Telecom standard was a coaxial pair having a 75? resistive impedance, this will normally be accepted as an alternative. The two interfaces are stated as alternatives in the CCITT Blue Book, Recommendation G (3) Telecom network and customer equipment which are directly connected at 2048 kbit/s should preferably use the same type of termination described above. The type of connection should be negotiated with Telecom locally. (4) Unless specifically negotiated otherwise with Telecom, two interfaces shall be provided as follows:- (a) One for the direction from customer equipment (or private network) to the Telecom network, and (b) One from the Telecom network to the customer equipment (or private network). 4.2 Cable connections Whether connection between Telecom network equipment and customer equipment is by means of 120? balanced screened pair or 75? coaxial pair, the maximum insertion loss shall not exceed 6 db at 1024 khz. 4.3 Earthing requirements (1) For 120? balanced pair ports, the screen of the pair shall be directly connected to earth at the output port only. Where possible however, provision should be made for possible future connection of the screen directly to earth at the input port. Earthing of a screen at both ends of a cable, even when it is of short length, has the effect of creating an 'earth loop' with resultant undesirable high frequency current flow. This can produce unwanted noise in the system. (2) For 75? coaxial ports, the outer conductor of the coaxial pair, shall be earthed as follows:- (a) The outer conductor of the output port shall be directly connected to earth as shown in Fig. 1 (a). 16

19 17 (b) The outer conductor of the input port coaxial cable shall be connected to earth through a 100 V capacitor having a value in the range 47 nf to 1000 nf, nominally 100 nf (see Fig. 1(b). (c) Provision shall be made at the input port to facilitate the future use of a direct earth (see Fig. 1 (c)) instead of the 100 nf capacitor described in (b). "Earth" used in this context should be the quietest available earth. 4.4 Power feeding If power feeding is required, it shall not be via any 2048 kbit/s input or output interface ports. 17

20 18 5 ELECTRICAL REQUIREMENTS 5.1 Bit rate The bit rate at the interface shall be 2048 kbit/s ± 50 ppm. 5.2 Coding Code HDB3 (High Density Bipolar code, order No. 3) shall be used and is defined as follows:- Ref. CCITT Blue Book, Recommendation G. 703, Annex A. (a) In this code, binary 1 bits are generally represented by alternative positive and negative pulses, and binary 0 bits by spaces. Exceptions are made when strings of four successive 0 bits occur in the binary signal. (b) The encoding of binary signals in accordance with these rules includes frame alignment bits, etc., where present. (c) Each block of four successive 0's is replaced by either '000V' or 'B00V'. 'B' represents an inserted pulse conforming to the AMI code, and, 'V' represents an AMI violation (i.e. where consecutive 1's are of the same polarity). (d) The choice of '000V' or 'B00V' is made such that the number of 'B' pulses between consecutive 'V' pulses is odd, i.e. so that successive 'V' pulses are of alternate polarity. Use of HDB3 coding ensures that no d.c. component is introduced. 5.3 Pulse shape (1) The pulse shape at the output port shall be nominally rectangular and shall comply with the limits stated in Table 1, and as shown in the mask indicated in Figure 2. (2) The pulse shape presented at the input port will be the same as for the output port, but modified by the characteristics of the connecting cable up to a maximum of 6 db. 18

21 19 TABLE 1: PULSE SHAPE REQUIREMENTS CHARACTERISTIC REQUIREMENT 75? Port 120? Port Nominal Peak Voltage of Pulse (mark) 2.37 V 3 V Peak Voltage Limits of non-pulse (space) 0 ± V 0 ± 0.3 V Nominal Pulse Width 244 ns Ratio of the Amplitudes of Positive Pulse to Negative Pulse at the Centres of the 0.95 to 1.05 Pulse Intervals Ratio of the Width of Positive Pulse to Negative Pulse at Half the Nominal Amplitudes 0.95 to Input port characteristics (1) The return loss at the input port against the appropriate test impedance (i.e. 120? resistive balanced or 75? resistive unbalanced) shall be equal to or greater than the following values:- FREQUENCY (khz) RETURN LOSS (db) 51 to to to (2) No errors shall result in a wanted signal when applied at the input port together with an interfering signal such that the signal-to-interference ratio is 18 db. The 'wanted' signal shall be a nominal aggregate signal, encoded into HDB3 and having a pulse shape compliant with this Section. (3) The characteristics of the 'interfering' signal shall be as follows:- (a) have the same pulse shape as the 'wanted' signal, (b) have a bit rate compliant with the limits of this Specification, (c) be not synchronous with the 'wanted' signal, and, (d) its binary content shall comply with CCITT Blue Book, Recommendation O. 151 (2 15-1bit period). (e) The two signals shall be combined in a combining network having zero overall loss in the signal path and with the appropriate nominal impedance (75? unbalanced or 120? balanced). 19

22 20 This ensures adequate immunity against signal reflections that can arise at the interface due to impedance irregularities at digital distribution frames and at digital output ports. 5.5 Synchronisation (1) It is recommended that customer equipment forming a private network connected digitally should be synchronised from one 'master' source. All other digital equipment thus functions as 'slave' to the nominated 'master'. Telecom has an established synchronisation hierarchy for its PSTN whereby all interworking component digital systems in the network are synchronised with one master source. This master clock has an accuracy of ±1 part in (2) A 'master' terminal derives its output bit timing from an internal clock and a 'slave' terminal derives its timing from incoming signals, and then synchronises its transmitted signals to them. (3) For customer equipment interfaces with the Telecom network, the following shall apply:- (a) Equipment shall be synchronised from a nominated 2048 kbit/s link from the Telecom network. (b) Failure of that link should result in the equipment being synchronised from an alternative Telecom link, by its own internal clock or from a nominated 'master' terminal in the private network. (c) Under no circumstances shall any customer equipment be set up to function as a 'master' to the Telecom network. It is recommended that systems free run within 50 ppm of the nominal 2048 kbit/s frequency on their own internal clock system, if all links with the Telecom network fail or are not available for any reason. 5.6 Jitter and wander (1) Jitter and wander are in fact similar phenomena occurring at different frequencies and it is necessary to exercise control to avoid excessive accumulation in any digital network. Failure to do so can result in errors and slips in the transmission of digital signals and a degradation of digitally encoded analogue information. Reference CCITT Blue Book, Recommendation G (2) For any 2048 kbit/s digital interface between customer equipment and the Telecom network, jitter and wander performance is specified as follows:- (a) Jitter and wander tolerance of an input interface shall comply with the limits in the mask shown in Fig. 3. Jitter and wander tolerance is the ability of equipment to accept phase deviations on incoming signals without introducing slip or errors. 20

23 21 (b) Jitter and wander present at an output interface (known also as intrinsic jitter) shall comply between the 20 Hz and 100 khz limits in the mask shown in Fig. 3. "UI" used in Fig. 3 is an abbreviation for "unit interval", which has a unique value for each separate digital bit rate. For 2048 kbit/s, UI = 1 /2048 = 488 ns. Ref. CCITT Blue Book, Recommendation G. 823, Clauses 2 & 3. 21

24 22 6 FRAME STRUCTURE 6.1 General (1) For all 2048 kbit/s interfaces carrying telephony and/or PCM multiplex systems, the characteristics of the frame structure shall comply with all requirements of CCITT Blue Book, Recommendation G. 704 which apply to 2048 kbit/s working. (2) Speech shall be A-law encoded in accordance with CCITT Rec. G (3) PCM multiplex equipment shall comply with the requirements of CCITT Blue Book, Recommendation G Bit allocation (1) The allocation of bits 1 to 8 (TS 0) of the 256 bit frame shall be as detailed in CCITT Blue Book, Recommendation G. 704, Clause (2) Telecom uses bit 3 in the frame "not containing frame alignment signal" for remote alarm indication as follows:- 0 = normal condition 1 = alarm condition (3) Bits 4-8 inclusive shall be accessible, even if not used initially, for possible use at a later date. 6.3 Cyclic redundancy check (CRC) (1) The CRC-4 procedure for providing protection against simulation of the frame alignment signal and for enhancement of error monitoring is described in CCITT Blue Book, Recommendation G. 704, Clause and G. 706, Clause 4. It involves special use of bit 1 in the the frame "containing frame alignment signal". (2) This procedure is used by Telecom on many, but not all, 2048 kbit/s digital streams. However, it is proposed that in the longer term it will be used universally to enhance monitoring of digital signals on a stage by stage basis, as shown if Fig. 4. When this facility is required, it will be specifically stated in the particular service or product specification applicable. (3) If provided on any equipment for which a Telepermit is required, this facility shall comply with CCITT Recommendation G. 704 and G Alarm and fault conditions (1) The fundamental characteristics, fault conditions, etc., together with the alarm facilities of any 2048 kbit/s digital stream interfacing with the Telecom network, shall conform to CCITT Blue Book, Recommendation G

25 23 (2) The bit error rate (BER) of the digital signal incoming to the Telecom network shall be better than 1 part in 10 7 when tested over any one minute period. (3) It is strongly recommended that adequate alarm facilities are provided for an interconnecting bit stream, particularly alarm indications to the end of the link under the control of Telecom. This indication is desirable so that adequate service protection to Telecom customers can be provided. Reciprocal arrangements can also be made so that any alarm supervision of the link is to the mutual benefit of both parties. (4) Details of such alarm arrangements and associated service protection responsibilities shall be clearly defined in any application for connection to the Telecom network. (5) Following is a list of alarm indications which are monitored and reported by Telecom. Alarm priorities should be negotiated with Telecom prior to connection of customer equipment:- (a) Loss of Frame Alignment (LOF): This is an indication that the received pattern (if any) does not contain the Frame Alignment word. (b) Loss of Multiframe Alignment (LOMF): This is an indication that the received pattern (if any) does not contain the Multiframe Alignment word. (c) Frame Pattern Error (FPE): This alarm indicates that a threshold bit error rate of ±1 part in 10 3 has been exceeded. (d) PCM Loss (PCML): This is an alarm which indicates a complete loss of incoming signal. (e) Alarm Indication Signal (AIS): This is an indication that the received pattern contains all digit '1's. (f) Remote Frame Alarm (RFA): This is a signal sent in the outgoing (send) direction of a digital link, in response to the LOF signal, indicating to the remote equipment that the incoming (receive) path has been disrupted. Conversely, an alarm is activated by the local equipment when a Remote Frame Alarm signal is received from the remote equipment. (g) Remote Multiframe Alarm (RMFA): This is a signal sent in the outgoing (send) direction of a digital link, in response to the LOMF signal, indicating to the remote equipment that the incoming (receive) path has been disrupted. Conversely, an alarm is activated by the local equipment when a Remote Frame Multiframe Alarm signal is received from the remote equipment. (h) Frame Alignment Memory Error (FAME): 23

26 24 This alarm indicates a bit error in the frame alignment memory. END OF TECHNICAL DOCUMENT TNA

27 25 APPENDIX 1 TNA 117 APP. 1 ISSUE 1 : 1992 SUMMARY OF COMPLIANCE STATEMENT REQUIREMENTS (1) This Appendix summarises requirements for a clause-by-clause compliance statement for Telepermit applications for customer equipment incorporating 2048 kbit/s interfaces. For full details of the necessary technical requirements, reference should be made to the main text. (2) These requirements are additional and complementary to those stated in the relevant PTC 200 series specification. (3) Since this Technical Document is not a formal test specification, the precise test methods and instrumentation are left to the discretion of the applicant and/or the test laboratory concerned. Numbering of the following text relates to the clause numbering used in the main body of the Technical Document for convenience of referencing. 4 PHYSICAL REQUIREMENTS 4.2 Cable connections Indicate type of port termination by a 'v' :- 120? Screened Pair:... 75? Coaxial Pair: Earthing requirements Screen or outer conductor earthed at output port only: COMPLIES YES/NO

28 TNA 117 APP. 1 ISSUE 1 : ELECTRICAL REQUIREMENTS Bit rate Bit rate requirement kbit/s ± 50 ppm: 5.2 Coding Requirement - HDB3: COMPLIES COMPLIES YES/NO YES/NO 5.3 Pulse shape Requirement - as Table 1 (Fig. 2): COMPLIES YES/NO 5.4 Input port characteristics (1) Return loss requirements: Frequency (khz) Return Loss (db) Complies ( v) 51 to to to FULLY COMPLIES YES/NO (2) Requirement: No errors in wanted signal at input port when combined with an unwanted signal when the two are combined as stated in clause 5.4 (3). COMPLIES YES/NO 5.6 Jitter & wander Requirement: Jitter and wander within limits expressed in Fig.3. COMPLIES YES/NO

29 TNA 117 APP. 1 ISSUE 1 : FRAME STRUCTURE General (1) Frame structure complies with CCITT Rec. G. 704? YES/NO (2) Speech is A-law encoded? YES/NO (3) PCM multiplex equipment complies with Rec. G. 732? YES/NO 6.2 Bit allocation (1) Bit allocation (bits 1 to 8) as Rec. G. 704? YES/NO 6.3 Cyclic redundancy check (3) Is CRC provided? YES/NO If 'YES', does it conform with CCITT Rec. G. 704 & G. 706 YES/NO 6.4 Alarm and fault conditions (2) Requirement: BER better than 1 part in COMPLIES YES/NO (4) Describe alarm arrangements: