CEPT T CD 01-10 E-1985 Engineering Requirements for a 1200 Bit s Duplex Modem for Use on the GSTN《在GSTN上使用的1200比特 秒双工调制解调器工程要求》.pdf

1、- CEPT T/CD*OL-LO*E 79 2326434 0003178 O=- (3 TCDO1-10 Page 1 E Recommendation T/CD 01-10 E (Ostende 1979, revised at Cannes 1983) concerning the engineering requirements for a 1,200 bit/s duplex modem for use on the general switched telephone network Recommendation proposed by Working Group T/WG 10

2、 “Data Communications” (CD) Text of the revised Recommendation adopted by the “Telecommunicatioiis” Commission: “The Conference of European Post and Telecommunications Administrations, Considering - that Recommendation T/CD 01-01 contains the text of the Specifications of the general engineering req

3、uirements - that working groupe CD has studied the harmonization of such modems under the auspices of Question CD 1. Recommends - that the attached Specification of engineering requirements for a 1,200 bit/s duplex modem as contained in the Annex to this Recommendation should be taken into account b

4、y ali CEPT Administrations when implementation of such types of equipment is being planned by Administrations.” for data circuit terminating equipment for analogue and digital networks; Administrations are free to stipulate additional requirements, and also which of the optional requirements, if any

5、, are to be provided. Note 1; This specification is subject of continuing study and possible amendment. Note 2; The Annex is an integral part of the Recommendation. e e I Edition of November 30, 1985 CEPT T/CD*OL-LO*E 79 2326434 0003379 2 p T/CD O1 -1 O E Page 3 Annex . Contents Section A . Coinitio

6、n requirements 5 1 . General. 5 2 . Data signalling rates 5 3 . Interfaces 5 4 . Modulation and coding . 6 5 . Scrambler and descrambler . 8 6 . Line signal levels . 9 7 . Testfacilities . 9 8 . Construction . 10 9 . Performance . 10 Section B . Network dependent requirements . 13 1 . General . 13 2

7、 . Fixed compromise equaliser . 13 O 3 . Additional guard tone . 13 Section C . Optional requirements 14 1 . Additional data signalling rates . 14 2 . Additional character size 14 3 . Additional interchange circuits 14 Extended signalling rate range in start-stop mode 14 5 . Controlled carrier opera

8、tion . 14 6 . Additional guard tone . 15 7 . Leased circuit operation 15 4 . CEPT T/CD*OL-LO*E 77 m 2326414 0003L80 7 m 1. 1.1. 1.2. 1.3. 2. 3. 3.1. T/CD O1 -1 O E Page 5 GENERAL This specifications and Recommendation T/CD 01-01 taken together define the facilities required from the modem. The modem

9、 is intended for use on connections on general switched telephone networks. The principal characteristics of this modem are as follows: (a) full duplex operation on 2-wire GSTN circuits; (b) channel separation by frequency division; (c) differential phase shift modulation for each channel with synch

10、ronous line transmission at 6 (nominal) ; (d) inclusion of a scrambler; (e) inclusion of test facilities. O baud The modem shall provide facilities for the transmission of synchronous and start-stop data at 1,200 bit/s. DATA SIGNALLING RATES The data rate transmitted to line shall be 1,200 bit/s 5 0

11、.01% with a modulation rate of 600 baud f0.01%. It shall be possible to configure the modem to accept either: i) synchronous data at 1,200 bit/s 50.01% under the control of circuit 113 or circuit 114; or ii) start-stop data at 1,200 bit/s + 1%, -2.5% with 9 or 10 or 11 bit/character. Selection of mo

12、de and character size shall be by manual means. INTERCHANGE CIRCUITS Table of interchange circuits The interchange circuits are listed in Table 1 shall be provided. Number 102 102a 102b 103 104 105 106 107 108/1 108/2 1 o9 113 114 115 125 140 141 142 Interchange circuit Description Signai ground or

13、common return DTE common return DCE common return Transmitted data Received data Request to send Ready for sending Data set ready Connect data set to line Data terminal ready Data channel received line signal detector Transmitter signal element timing (DTE source) Transmitter signal element timing (

14、DCE source) Receiver signal element timing (DCE source) Calling indicator Loopback/maintenance test Local loopback Test indicator Table 1. Interchange circuits (Note 1). Essential Note 2 Note 2 Note 3 Note 4 Note 4 Note 5 Note 6 Note 6 Note 7 Note I: All essential interchange circuits and any others

15、 which are provided shall comply with the functional and operational requirements of Recommendation T/CD 01-01. All interchange circuits provided shall be properly terminated in the data terminal equipment. Note 2: Interchange circuits 102a and 102b are required where the electrical characteristics

16、defined in Recommendation V.10 are used. Note 3: Some automatic calling equipments are designed to emit a calling tone to line by turning on circuit 105 to the calling modem. The general switched telephone network (GSTN) constant carrier handshake in such that no calling tone will be emitted by the

17、Y.22 modem when used with these equipments. Edition of November 30, 1985 CEPT T/CD*OL-LO*E 232b414 0003LBL O = O0 o1 11 IO T/CD O1 -10 E Page 6 + 90“ O“ + 270“ + 180“ Note 4: This circuit shall be capable of operation as circuit 108/1 or 108/2 depending on its use. For automatic calling, it shall be

18、 used as lOSj2 only. Note 5; When the modem is not operating in a synchronous mode any signals on this circuit shall be disregarded and the data terminal equipment may not have a generator connected. Note 6: When the modem is not operating in a synchronous mode, this circuit shall be clamped to the

19、OFF condition and the data terminal equipment may not terminate the circuit. Note 7; This circuit is for use with the general switched telephone network only. 3.2. Circuits 106 and 109 response times Circuit 106 response times, which are from the application of an ON and OFF condition on circuit 105

20、, shall be: OFF to ON 62ms ON toOFF 62ms Circuit 109 response times shall be: OFF to ON 105 to 205 ms ON to OFF 10 to 24 ms See also Section 4.8. for operating sequences. 4. MODULATION AND CODING 4.1. Carrier and guard tone frequencies The carrier frequencies shall be 1,200I 0.5 Hz for the low chann

21、el and 2,400f 1 Hz for the high channel. A guard tone of 1,800 Hzf20 Hz shall be transmitted at all times when the modem is transmitting in the high channel. The guard tone shall not be transmitted when the modem is transmitting in the low channel. 4.2. Line signal encoding The data stream to be tra

22、nsmitted shall be divided into groups of 2 consecutive bits (dibits). Each dibit shall be encoded as a phase change relative to the phase of the preceding signal element (see Table 2). At the receiver, the dibits shall be decoded and the bits re-assembled in correct order. The left-hand digit of the

23、 dibit is the one occurring first in the data stream as it enters the modular portion of the modem after the scrambler. 1 Dibit value I Phase change I Table 2. Line encoding. Note 1: The phase change is the actual on-line phase shift in the transition region from the centre of one signalling element

24、 to the centre of the following signalling element. 4.3. Spectrum and group delay characteristic After making allowance for the nominal specified compromise equaliser characteristic the transmitted line signal shall have a frequency spectrum equivalent to the square root of raised cosine shaping wit

25、h a 75% roll-off and within the limits of Figure 1. Similarly, the group delay of the transmitter output shall be within I100 microseconds over the frequency range 800 Hz-1,600 Hz (low channel) and 200 Hz-2,800 Hz (high channel). 4.4. Received signal frequency tolerance Noting that the frequency tol

26、erance of the transmitter carriers is f 1 Hz or less, and assuming a maximum shift of +6 Hz in the connection, the receiver shall meet the specified performance requirements with a received frequency offset up to f7 Hz. 4.5. Synchronous operation In the synchronous mode, the modem shall accept synch

27、ronous data at 1,200 bit/s f 0.01 % from the DTE on circuit 103 under control of circuit 113 or circuit 114. The data shall then be scrambled in accordance with Section 5 and then passed to the modulator for encoding in accordance with Section 4.2. a Edition of November 30, 1985 4.6. 4.6.1. 4.6.1.1.

28、 4.6.2. 4.6.2.1. T/CD O1 -1 O E Page 7 Start-Stop Operation Trmsmit ter In the start-stop mode, the modem shall accept a data stream of start-stop characters from the DTE at a nominal rate of 1,200 bit/s. The start-stop data shall be converted to a form suitable for transmission synchronously at 1,2

29、00 bit/s viz: (a) a one unit start element, followed by 7 data units, and a stop element of one unit in length (9 bit characters); (b) a one unit start element, followed by 8 data units, and a stop element of one unit in length (10 bit characters) ; (c) a one unit start element, following by 9 data

30、units, and a stop element of one unit in length (11 bit characters). The character format selected shall be the same for both transmitter and receiver. The characters shall be in accordance with Recommendation V4. It shall be possible to transmit characters contiguously or with any additional contin

31、uous stop element of arbitrary length between characters. Note: In each of the formats, data units can be replaced by additional stop units. For example, format (c) will allow 11 bit characters consisting of a one unit start element, followed by 8 data units and a stop element of 2 units to be handl

32、ed. The intracharacter signalling rate (signalling rate of the start bit and information bits within each character) provided by the DTE on circuit 103 must be 1,200 bit/s + 1%, -2.5%. The character rate (the reciprocal of the time interval between successive start bits) provided by the DTE over cir

33、cuit 103 must not exceed: 134.7 characters per second for 9 bit characters 121.2 characters per second for 10 bit characters 110.2 characters per second for 11 bit characters When the character rate is: from 133.3 to 134.7 characters per second for 9 bit characters from 120.0 to 121.2 characters per

34、 second for 10 bit characters from 109.1 to 110.2 characters per second for 11 bit characters the start-stop to synchronous converter in the modem transmitter shall as aften as is necessary delete the stop bits of the incoming characters. No more than one stop bit shall be deleted for any 8 consecut

35、ive characters. When the character rate provided by the DTE on circuit 103 is less than: 133.3 characters per second for 9 bit characters 120.0 characters per second for 10 bit characters 109.1 characters per second for 11 bit characters the start-stop to synchronous converter in the modem is transm

36、itting more bits per second than are provided by the DTE. The converter shall therefore insert extra stop bits in between the transmitted characters. Break signal If the converter detects M to 2M + 3 bits all of “start” polarity, where M is the number of bits per character in the selected format, th

37、e converter shall transmit 2M + 3 bits of “start” polarity. It the converter detects more than 2M + 3 bits all of “start” polarity the converter shall transmit all these bits as “start” polarity. Note: The DTE must transmit on circuit 103 at least 2M bits of “stop” polarity after the “start” polarit

38、y break signal before sending further data characters. This ensures the receiving modem can regain character synchronism. Receiver The intracharacter signalling rate provided to the DTE over circuit 104 shall be in the range 1,200 to 1,221 bit/s. The nominal length of the start and data elements for

39、 all characters shall be the same. The length of the stop element shall not be reduced by more than 12.5% to allow for overspeed in the transmitting terminal. Break signal The 2M+3 or more bits of “start” polarity received from the transmitting modem shall be output on circuit 104. The modem shall t

40、hen regain character synchronism from the following “stop” to “start” transition. Edition of November 30, 1985 CEPT T/CD*OL-LO*E D 232b43i.I 0003383 4 T/CD 01-10 E Page 8 4.7. 4.7.1. 4.7.2. 4.7.3. 5. 5.1. Operating sequences Channel allocation On the general switched telephone network, the modem at

41、the calling data station shall transmit in the low channel and receive in the high channel (call mode). The modem at the answering data station shall receive in the low channel and transmit in the high channel (answer mode). Note: Where calls are established on the GSTN by operators, bilateral agree

42、ment between users on channel allocation will be necessary. Automatic answering sequence The automatic answering sequence defined in Recommendation T/CD 01-01 shall be transmitted from the answer mode on GSTN connections. GSTN handshake sequence The means of achieving initial synchronism between the

43、 call mode modem and the answer mode modem on GSTN connections is shown in Figure 2. Call mode modem Once the call mode modem has connected to line, it shall be conditioned to receive signals in the high channel and shall apply an ON condition to circuit 107 in accordance with Recommendation T/CD 01

44、-01. The modem shall remain silent until unscrambled binary 1 is detected for 155 f 50 ms, and after waiting for 456f 10 ms shall transmit scrambled binary 1 in the low channel. Upon detecting scrambled binary 1 in the high channel in 270f40 ms, the modem shall turn circuit 109 ON, the wait a furthe

45、r 765f 10 ms. Circuit 106 shall then respond to the condition of circuit 105 in accordance with Section 3.2. When circuit 106 of OFF, circuit 103 shall be clamped to the binary 1 condition. Answer mode modem Once the answer mode modem has connected to line, and immediately following the CD/LM I answ

46、er sequence, the modem shall be conditioned to receive signals in the low channel. It shall then apply an ON condition to circuit 107 and transmit unscrambled binary 1. Upon detecting scrambled binary 1 or O in the low channel in 270 Bi- ;-, binary i II Icrambled binary i Data ai and 1,800 Hz I Wait

47、 765I i0 ms I I 106 104 clamped to binary 1 Binary I Data Figure 2. GSTN handshake sequence (with auto-answer sequence). Edition of November 30, 1985 CEPT T/CD*OL-LO*E 2326434 0003388 3 T/CD O1 -10 E Page 13 Section B. Net work dependent requirements 1. GENERAL This section specifies national networ

48、k dependent requirements which may be included at the discretion of the Administration. 2. FIXED COMPROMISE EQUALISER Fixed compromise equalisation shall be incorporated in the modem. Such equalisation shall be equally shared between transmitter and receiver. The characteristics of the equaliser sha

49、ll be as specified by the purchasing Administration. 3. ADDITIONAL GUARD TONE See Section C 6. Edition of November 30, 1985 CEPT T/CD*OL-LO*E D 2326434 0003187 5 T/CD O1 -10 E Page 14 Section C. Optional requirements 1. ADDITIONAL DATA SIGNALLING RATES 1.1. 600 bit/s Facilities shall be provided to permit transmission of synchronous and start-stop data at 600 bit/s nominal. The data rate transmitted to line shall be 600 bit/s f 0.01% with a modulation rate of 600 baud +0.01%. Each bit shall be encoded as a phase change relative to the phase of the preceding signal element