30-BAUD PRIVATE LINE CHANNELS

Transcription

1 BELL SYSEM Plant Seies PRACCES SECON ssue 1, July 1970 A&Co Standad 30-BAUD PRVAE LNE CHANNELS NERFACE SPECFCAON 1. GENERAL NRODUCON 1.01 he pupose of this specification is to define the inteface between the 30-Baud Pivate Line Channel and a Custome-Povided (CP). he 30-Baud Pivate Line Channel is capable of tansmitting diect-cuent makspace o binay signals at ates up to 30-Bauds fo meteing, supevisoy contol, and miscellaneous signaling puposes. he 30-Baud channel may not be used fo tansmission of signal elements whose nominal duation is less than 33.3 milliseconds. Within the speed capability of the channel, tansmission is code and speed insensitive. hese channels ae funished fo one-way opeation on a two-wie basis, and fo half-duplex (two-way, nonsimultaneous) opeation o fo full duplex (two-way, simultaneous) opeation on a fou-wie basis at the inteface. Metallic continuity, end-to-end, howeve, is not a equiement of this channel and will geneally not be available. BACKGROUND AND PHLOSOPHY 1.02 he 30-Baud channel has evolved ove the yeas pimaily to meet the need fo a low speed signaling channel with a contact closue input and output sufficient to dive electomechanical elays. Cuent athe than voltage is the significant paamete. he 62.5 ma mak, O ma space neutal cuent loop, is the aangement most commonly available, but thee is also some use of 20 ma mak signal levels to hold down the cost of poviding the sevice. heefoe, it is suggested that CP equipment using these channels be designed to wok with eithe level of making cuent; eithe diectly o by a wiing option. VARAONS FROM SANDARD ARRANGEMENS 1.o3 n low speed signaling systems whee an aangement, which is not compatible with this specification is equied, o additional sevice featues ae desied, special aangements must be made with the local elephone Company epesentatives. n some of these systems it may be detemined that eithe a taiff othe than the 30-Baud Channel applies o a special contact with the elephone Company is equied. An example of such a special aangement might be fo an inteface that is descibed in the Electonics ndusties Association specification RS-232-B. 2. DESCRPON PHYSCAL 2.01 Nomally, a teminal block having 6-32 scews will be povided by the elephone Company to seve as an inteface between the 30-Baud Channel and the CP. Figue 1 shows typical send-only, eceive-only, half-duplex, and full-duplex inteface aangements. he channel side of the inteface teminal block will appea as one o two pai of wies connecting to the seving telephone office o to tansmission equipment supplied by the elephone Company and located on the custome s pemises. he need fo, and type of, tansmission equipment will be detemined by the elephone Company. Space fo this equipment shall be povided by the custome. he CP side of the inteface should consist of one pai of wies connected to the input of the CP and one pai of wies connected to the output of the CP as shown in Figue 1. POWER REQUREMENS 2.02 n systems whee the elephone Company povides tansmission equipment at the inteface, the custome must povide a souce Ameican elephone and elegaph Company, 1970 Pinted in U.S.A. Page 1

2 SECON continuous 117 volt, 60 Hz ac powe fom a nonswitched outlet. he equipment supplied by the elephone Company will wok popely ove a voltage ange of 105 to 129 volts and a fequency deviation of ~0.45 Hz. he powe eceptacle povided must accept a U-bladegound type plug and supply a valid gound to the gound pin. he powe consumption will not exceed 70 watts pe channel. Whee tansmission equipment is not povided, the custome does not need to povide any powe fo the 30-Baud Channel. ENVRONMEN 2.03 n systems whee the elephone Company povides tansmission equipment at the inteface,the ambient tempeatue should be in the ange of 4W to 12&F and the elativehumidity should be in the ange of 20 pecentto 95 pecent. 3. inerface ELECRCAL CHARACERSCS CHANNEL SGNALS 3.01 he signals at the inteface will be eithe milliampees o 62.5 ~2.5 milliampees neutal signals (cuent no cuent). he value of de voltage selected by the elephone Company to supply this cuent will vay depending on local conditions and the type of tansmission equipment used. he tip () o ing (R) side of the send data (SD) teminals o eceive data (RD) teminals may have a potential of O up to 135 volts dc to gound (positive o negative). Fom 24 volts up to 270 volts dc may exist acoss the SD teminals when the CP send contact is open (station sending a space signal). Polaity is such that cuent flow though the CP is fom ing to tip; i.e., the ing side is positive with espect to tip. dentification of the teminals will be funished by the elephone Company who will also make the de cuent adjustments. NPU OF HE CP 3.02 he input (eceive side) of the CP should appea to the channel as a cicuit having a fixed esistance of less than 150 ohms and an inductance of less than 0.5 Heny. (Non-inductive impedances ae pefeed as they cause less CP send contact deteioation.) he eceiving cicuity should be isolated fom gound (leakage at least 1.0 megohm) and should not impess foeign voltages in excess of 12 volt on the inteface teminals. OUPU OF HE CP 3.o3 he output (send side) fom the CP should appea as a set of contacts o thei electical equivalent (isolated fom gound) capable of epeatedly making and beaking a nominal 62.5 milliampees at up to 270 volts dc. When the contacts ae open, the esistance acoss the contacts should be at least one megohm and when closed, the contact esistance should be less than 5 ohms. Any device used to monito the output of the CP should not inset moe than 150 ohms and less than 0.5 Heny inductance in seies with the send contacts. (Relays having dy eed contacts have not poven satisfactoy fo this application. ) f mechanical o mecuy wetted contacts ae used, it is ecommended that a spak suppession netwok be povided in the CP to educe electical cicuit noise and pevent excessive contact eosion. Nominal values of the spak suppession cicuit components should be a esistance of 470 to 1000 ohms in seies with a capacitance of O. mico faad. 4. RANSMSSON CHARACERSCS OF CHANNEL SGNAL DSORON RANSON DSPLACEMEN 4.01 Fo the pupose of this specification, tansition displacement is defined as the time displacement of a mak-to-space o a space-to-mak tansition fom its ideal instant. he andom tansition displacement, measued at the i!io~o point of the ising and falling wavefom, caused by the channel nomally will not exceed 10 mill=onds in eithe diection (ealy o late). he 10 millisecond value does not include any allowance fo tansition displacements intoduced by a tansmitting CP. Figue 2 compaes typical tansmitted and eceived wavefoms at the inteface. PROPAGAON ME ABSOLUE DELAY 4.02 Signal popagation time will vay depending on the paticula type and length of the line facilities and type of tansmission equipment (if any) povided at the inteface. t is expected that the one-way popagation time will geneally be less than 14 second. Channel tunaound time, which is elated to popagation time and is a function of the complexity and length of the channel, is not specified. f popagation time o tunaound time is an impotant Page 2

3 1SS 1, SECON facto in poviding sevice, the local elephone o inteuption occus. f the channel goes into a Company epesentative should be consulted fo steady spacing condition (no cuent on the RD moe exact infomation concening a specific channel. leads), this indicates a channel failue and the CP equipment may use this signal condition as a CHANNEL FALURE channel failue indication, if so desied. Howeve, cetain channel failue conditions may not cause a 4.o3 No sepaate leads ae bought out at the steady space to occu on the RD leads. inteface to indicate when a channel failue 30 BAUD CHANNEL NERFACE ARRANGEMENS 30 Baud Channel wgl Custome Povided.. % g !=,1 Local loop to Optional ~ - elco - ansmission elco Cental Office! Equipment + R J Block S D 1 1 X!QQN4J Contact Potect ion Send Contact - Loca loopto, elco Cental Office ~ L Optional elco ansmission Equipment Receive Cicuit O Relay Fig. 8 Block l Receive Only (Cent d on Next Page) Page 3

4 SECON BaudChannel Custome Pwided * (} Send Contact Local loop to - elco - ~1 Contact Potect ion elco Cental Office ~ Equipment L Receive RD 9. Cicuit Block,R HALF DUPLEX O Relay 1 Local loop(s)to ~ SD ~ Optional 4 R elco - elco Cental Office ansmlsslon ~ Equipment - Ungoutied - Recewe RD ~ L J Cicuit O Relay Blcck i FULL DUPLEX Fig. l (Continued) Page 4

5 Mak ~ m@ cj 62.5 ma Space~ -O ma -d-z +z e + -l++ e ++ + RANWED SGNAL (UNDSORED) 420 C62.5 ma +Oma J?ECE VED ~lgna~(dsored) Notes: 1)e = Shotest element in the tansmitted signs 1. 2) At = ansition displacement caused by the 30 baud channel. 3) Baud Rate= 1 %(in seconds) 4) Received wavefom S geneally not a squae wave 5) Slicing level is assumed to be at th?! 5W0point of the ising and falling wavefom. Fig. 2 Received Signal..