1、CEPT T/CD*OL-OB*E 79 2326434 0003339 L T/CDQ-08 Page E 1 Recommendation T/CD O1 -08 E (Ostende 1979, revised at Cannes 1983) concerning the engineering requirements for a parallel data transmission modem for use in the general switched telephone network Recommendation proposed by Working Group T/WG
2、10 “Data Communications” (CD) Text of the revised Recommendation adopted by the “Telecommuiiicatiois” Commission : “The Conference of European Post and Telecommunications Administrations, Consider ihg - that Recommendation T/CD 01-01 contains the text of the Specifications of the general engineering
3、 requirements - that working group CD has studied the harmonization of modems under the auspices of Question CD 1. for data circuit terminating equipment for analogue and digital networks; Recommends - that the attached Specification of engineering requirements for a parallel data transmission modem
4、 for use in the general switched telephone network as contained in Annex I to this Recommendation should be taken into account by all CEPT Administrations when implementation of such a piece of equipment is being planned by Administrations are free to stipulate additional requirements, and also whic
5、h of the optional requirements, if any, are to be provided. Note 1: The Specification is subject of continuous study and possible amendment. Note 2: The Annex is an integral part of the Recommendation. O Administrations. Edition of November 30, 1985 T/CD 01-08 E Page 3 Annex 1. Contents Section A. C
6、omtnon requirements . 5 1. General 5 2. Data signalling rates . 5 3. Interfaces., 5 3.1. Instation modem interface 5 3.2. Outstation modem interface. . 6 3.3. Electrical characteristics . 6 4. Modulation and coding 7 5. Scrambling (not provided for) . 7 6. Timing . 7 7. . Backward channel 7 8. Line
7、signal characteristics. 7 9. Out-of-band interference . 8 10. Performance requirements. 8 11. Testing and measuring requirements. 8 12. Construction 9 13. Specific design requirements 9 14. Power supply 9 15. Environmental requirements 9 O Section B. Network dependent requirements No specific requir
8、ements. Parts of this specification which are literally copied from CCITT-Recommendations, are marked with a line in the margin of the paper. Sections which need further study, are marked with an asterisk. Edition of November 30, 1985 CEPT T/CD*OL-OB*E W 232b414 0003141 T = a a T/CD O1 -08 E Page 5
9、Section A. Common requirements 1. GENERAL The modems for parallel data transmission for one-way data transmission, where a large number of low-cost sending stations (outstations) transmit to a central receiving station (instation) are intended for use in the general switched telephone network only.
10、The modems must meet the requirements given in the Specification of the general engineering requirements (Recommendation T/CD 01-01) and in this specification. They must comply with CCITT Recommenda- tions V.20, V.241V.28 and V.31. The main characteristics of these recommended modems (outstation mod
11、em/instation modem) for parallel data transmission are as follows: (b) transmission of 64-character combinations from outstation to instation; (a) transmission of 16-character combinations (c) transmission of 256-character combinations (d) transmission of simple acknowledgement signals or analog sig
12、nals (voice-answering) from the instation to the outstation. The parallel data transmission system uses two or three times one out of four frequencies. 1 2. DATA SIGNALLING RATES The modulation rate is up to 40 characters per second. In the 16-character combination system the data signalling rates s
13、hall be up to 20 or up to 40 characters per second, in the other combination systems the data signalling rates shall be up to 20 characters per second. 3. INTERFACES 3.1. Instation modem interface The interchange circuits to be used are given in the list below. List of interchange circuits: 102 104
14、105 107 Data set ready. i08/1 Connect data set to line (see Note I). 109 118 120 121 125 Calling indicator. 130 191 i i0 124 Select frequency groups. 13 1 Received character timing. Note 1: These circuits shall be capable of being used as circuits 108/1: Connect data set to line or circuit 108/2: Da
15、ta terminal ready, depending upon its use. For automatic calling it shall be used as 108/2. Note 2: These circuits are required if the 75 bit/s frequency modulated backward channel is provided in the modem (see also Note 4). Note 3: This circuit is required if the 5 bit/s amplitude modulation backwa
16、rd channel is provided in the modem. Note 4; The pin allocation on the interface connector is the same for circuits 191A and 121 and 191B and 118, respectively. If both, the speech channel and the 75 bit/s backward channel shall be provided in the modem, means have to be provided to switch between t
17、hose circuits. The functions of the above interchange circuits are defined in the Specification of the general engineering requirements (Recommendation T/CD 01-01) and comply with CCITT Recommendation V.24. Signal ground or common return. Received data, 12 or 8 circuits depending on whether group B
18、is used or not. These received data circuits are designated Al, A2 . C4, each corresponding to its relevant frequency (see Table i). Request to send (see Note 2). 10812 Data terminal ready 1 Data channel received line signal detector. Transmitted backward channel data (see Note 2). Transmit backward
19、 channel line signal (see Note 2). Backward channel ready (see Note 2). Transmit backward tone (see Note 3). Transmitted voice answer (see Note 4). Data signal quality detector. Edition of November 30. 1 985 CEPT T/CD*OL-O*E 2326434 0003342 3 TICD O1 -08 E At outstation closing of circuit 1 2 3 None
20、 Page 6 3.1.1. 3.1.2. 3.1.3. 3.2. 3.2.1. 3.3. Number of the channel on line At instation negative polarity on circuit 1 1 2 2 3 3 4 4 Interchange circuit connector The allocation of the interchange circuits to pins of the connector is in conformance with IS0 Standard 2110. It is given in Figure 1. E
21、lectrical characteristics The electrical characteristics of the above interchange circuits are given in the Specification of the general engineering requirements (Recommendation T/CD O1 -01) and comply with CCITT Recommendation V.28. Electrical characteristics of interchange circuit 191 The impedanc
22、e and transmitter requirements must comply with the line requirements for the modem, which are given in the Specification of the general engineering requirements (Recommendation T/CD O1 -01). Outstation modem interface The interchange circuits to be used are given in the list below. List of intercha
23、nge circuits: 102 103 105 Request to send. 107 Data set ready. 108/1 108/2 Data terminal ready 119 122 125 Calling indicator. 129 Request to receive. Note 1: This circuit shall be capable of being used as circuit 108/1 “Connect data set to line” or circuit 108/2 “Data terminal ready”. For automatic
24、calling it shall be used as 108/2. Note 2: The transmitted data circuits (103) will all use the same common return (102). The control circuits may operate each on their own return circuit. Note 3: The pin allocation on the modem interface connector is the same for circuits 192 and 119. If both, the
25、speech channel and the 75 bit/s backward channel shall be provided in the modem, means have to be provided to switch between those circuits. Note 4: This circuit carries the data of the 5 bit/s amplitude modulated backward channel, if provided. Signal ground or common return (see Note 2). Transmitte
26、d data (nine or six circuits depending on whether group B is used or not). These circuits are designated Al, A2 . C3, each corresponding to its relevant frequency (see Table 1). (Note I). Connect data set to line Received backward channel data (Note 3). Backward channel received line signal detector
27、 (Note 4). Correspondence fi Not more than one circuit per group may be closed at a time. Interchange circuit connector The allocation of the interchange circuits to pins of the connector is in conformance with IS0 Standard 21 10. It is given in Figure 2. Electrical characteristics The electrical ch
28、aracteristics of the above interchange circuits are given in the Specification of the general engineering requirements (Recommendation T/CD O 1-01) and comply with CCITT Recommendation V.3 1, except circuit i 19. The electrical characteristics for this interchange circuit are for further study. Edit
29、ion of November 30, 1985 4. 5. 6. 7. 7.1. 7.2. 8. 8.1. 920 Hz 1,320 Hz 1,720 Hz CEPT T/CD*OL-O*E 79 H 232b414 0003343 3 H 1,000 Hz 1,080 Hz 1,160 Hz 1,400 Hz 1,480 Hz 1,560 Hz 1,800 Hz 1,880 Hz 1,960 Hz TICD O1 -08 E Page 7 MODULATION AND CODING Channel Group ll2I3l4 Table 1. For the 16-character sy
30、stem only groups A and C are used. During the time no input data circuits are operated rest frequencies are sent to the line; the highest frequency in each group is recommended to be the rest frequency. SCRAMBLING: not provided for. TIMING In the 16-character system for the signalling rate up to 40
31、characters per second the timing channel shall consist of the frequencies F, = 1,400 Hz and FB3 = 1,480 Hz. In the 256-character system this timing channel shall be used to identify the two halves of an 8 bit character (2* = 16 x 16). The higher frequency is transmitted simultaneously with the fist
32、half of the character. No timing channel is provided in the 16-character and the 64-character combination systems for the signalling rate up to 20 characters per second. BACKWARD CHANNEL For the backward channel two non-exclusive options exist. Amplitude modulated 5 bit/s backward channel The freque
33、ncy of the amplitude modulated backward channel for audible and electrical signalling shall be 420 Hz. This tone may be amplitude modulated at rates of up to 5 bit/s. Frequency modulated 75 bit/s backward channel The modulation rate and characteristic frequencies for this backward channel are as fol
34、lows : (Symbol 1, mark) 420 Hz 480 Hz Modulation rate up to 75 bauds. In the absence of any signal on the backward channel interface, the condition Z signal is to be transmitted. The frequency modulated backward channel can be used simultaneously with the forward data frequencies. Fz FA (Symbol O, s
35、pace) LINE SIGNAL CHARACTERISTICS The transmit power levels shall be adjustable as indicated in the Specification of the general engineering requirements (Recommendation T/CD 01-01). Data channels The frequencies of the groups are transmitted parallel, the line signal consists of one and only one fr
36、equency of every group. Depending which combination system ist used the line signal consists either of two frequencies (of groups A and C) or of three frequencies (of group A, B and C). In 90th cases the transmit power level shall be the same. The tolerances on the data frequencies should be +4 Hz.
37、The tolerance on the level difference of the single frequencies shoud be less than ,O dB. Edition of November 30, 1985 CEPT T/CD*OL-OB*E 2326414 0003344 5 T/CD O1 -08 E Page 8 8.2. 8.3. 8.3.1. 8.3.2. 9. 1 o. 11. 11.1. 11.2. Backward channel Provision shall be made for the following facilities: (a) a
38、 speech channel non-simultaneous with forward data; (b) an amplitude modulated 5 bit/s backward channel for audible signals or/and electrical signalling (see Section A 7.1.); (c) a frequency modulated 75 bit/s backward channel for electrical signalling (see Section A 7.2.). For the speech channel th
39、e signal specifications shall be the same as for the telephone channel indicated in the specification of the general engineering requirements (Recommendations T/CD O1 -01). The toler- ances on the backward channel frequencies (420 Hz, 480 Hz) should be f4 Hz. Threshold levels Threshold levels of the
40、 data channel received signal detector When the level of the received signal in group C exceeds -49 dBm, circuits 109 shall be ON. When the level of this received signal is less than -54 dBm, circuit 109 shall be OFF. The detector circuit which causes circuit 109 to turn ON or OFF shall exhibit hyst
41、eresis action such that the level at which the OFF to ON transition occurs shall be at least 2 dB greater than that for the ON to OFF transition. Group C was chosen for this purpose because it is the most critical from a received level point of view. Threshold levels of the backward channel The expe
42、cted minimum level for the amplitude modulated backward channel is 43 dBm for the 420 Hz. Level of the received line signal of the frequency modulated backward channel: greater than 43 dBm less than -48 dBm The condition of circuit 122 for levels between -43 dBm and -48 dBm is not specified except t
43、hat the signal detectors shall exhibit a hysteresis action such that the function OFF to ON transition occurs is at least 2 dB greater than that for the ON to OFF transition. circuit 122 ON; circuit 122 OFF. OUT-OF-BAND INTERFERENCE The limits of the line signal spectrum shall conform to the require
44、ments indicated in the Specification of the general engineering requirements (Recommendation T/CD O1 -01). PERFORMANCE REQUIREMENTS The performance of the equipment will be evaluated by testing in accordance with the Specification for the general engineering requirements (Recommendation T/CD 01-01).
45、 In addition to those requirements the following requirements regarding error rate limits and parallel distortion limits apply. The character error rate under GSTN test conditions shall be less The parallel distortion, that means the time difference of the demodulation in the single frequency groups
46、 shall be less 2 ms. TESTING AND MEASURING REQUIREMENTS To be able to find the source of errors during a transmission procedure (whether it is in the modem or on the line or in the data terminal equipment), the modem shall offer test possibilities. Test of the instation modem The instation modem sha
47、ll have a unit which-irrespective of whether the data terminal equipment is connected or not-hecks the received data signals. If the received data signal is correct, an audible signal is sent to the transmitted station. Test of the outstation modem The test of the outstation modem shall be performed
48、 in cooperation with an instation modem. Irrespective of whether the data terminal equipment is connected to the modem or not, it shall be possible by means of switches (a) to transmit the rest frequencies FA, = 1,160 Hz and F, = 1,960 Hz in the 16-character combinations system, or FA4 = 1, I60 Hz,
49、F, = 1,560 Hz and F, = 1,960 Hz in all other combination systems, and (b) to switch on the receiver and give a visible signal if a backward signal is recognized correctly. a Edition of November 30. 1985 Page 9 12. 12.1. 12.2. 12.3. 13. 14. 14.1, 14.2. 15. CONSTRUCTION Instation modem The requirements are given in the Specification of the general engineering requirements (Recommendation T/CD 01-01). Outstation modem The size of the modems must be such that they can be placed beneath telephone sets. The modems shall be capable of being sealed. AU functional units of the modem
