1、a CEPT T/CD*OL-O4*E m 232b414 0003037 4 W 0 Page E 1 Recommendation T/CD O1 -04 E (Ostende 1979, revised at Cannes 1983) concerning the engineering requirements for a 2,400 bit/s modem for use on telephone type circuits Recommendation proposed by Working Group T/WG 10 “Data Communications” (CD) Text
2、 of the revised recommendation adopted by the “Telecommunications” 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 requirements - that Working Group CD
3、 has studied the harmonization of modems under the auspices of Question CD 1. for data circuit terminating equipment for use on voiceband, baseband and groupband circuits; Recommends - that the attached specification of engineering requirements for a 2,400 bitis modem for use on telephone type circu
4、its as contained in Annex 1 to this Recommendation, should be taken into account by all CEPT Administra- tions when implementation of such a piece of equipment is being planned by Administrations.” Note 1: Administrations are free to stipulate additional requirements, and also which of the optional
5、requirements, if any, are to be provided. Note 2: The specification is subject of continuing study and possible amendment. Note 3: Bars at the left-hand margin indicate that the wording of this specification is identical with CCIT Recommendation V.26bis for the relevant item. a Edition of November 3
6、0, 1985 Section A. Basic requirements. 1. General . 2. Data signalling rates. , . . 3. Interfaces 4. Modulation and coding. 5. Scrambling. . 6. Timing . 7. Backward channel. 8. Line signal characteristics . 9. Out-of-band interference . . 10. Performance requirements . TfCD 01-04 E Page 3 Annex 1. C
7、ontents 5 5 5 5 5 6 6 6 6 6 6 11. Testing and measuring requirements . 9 12. Construction. 9 13. Power supply. 9 14. Environmental requirements. 9 Section B. National network dependent requirements (No requirements) Section C. Optional requirements. . 10 1. General . 10 2. Data signalling rates. . 1
8、0 3. Interfaces 10 4. Modulation and coding. 12 5. Scrambling 12 6. Timing . 12 7. Backward channel. 12 8. Line signal characteristics . 14 9. Out-of-band interference 15 10. Performance requirements 15 O . 11. Testing and measuring requirements . No additional requirements. 14. 15 15. A 16. Other r
9、equirements 15 Edition of November 30, 1985 CEPT T/CD*01-04*E 79 m 2326434 0003039 m - T/CD O1 -04 E Page 5 Section A. Basic seqiiisenients 1. 1.1. 1.2. 1.3. 2. 2.1. 2.2. 3. 4. 4.1. 4.1. 4.1.2. 4.1.3. GENERAL Together with some optional requirements (Section C) this document forms a modem specifkati
10、on. The principal characteristics of this modem are based on CCITT Recommendation V.26bs. Parts of this specification which are copied verbatim from the afore-mentioned recommendation, are marked with a line in the left-handed margin of the paper. The modem shall meet the “General engineering requir
11、ements for DCEs“ (Recommendation T/CD 01-01). Principal characteristics - use of a data signalling rate of 2,400 bit/s and a modulation rate of 1,200 baud; - inclusion of automatic answering equipment in conformity with CCITT Recommendation V.25; - optional reduced rate capability at 1,200 bit/s ad
12、1,200 baud; - optional inclusion of a backward channel at modulation rates up to 75 baud. DATA SIGNALLING RATES The data signalling rate shall be 2,400 bit/s - evaluate transmission quality; (with the aid of these signals, a pattern analogous to the well-known eye-pattern can be made visible on e.g.
13、 an oscilloscope; so, for example in cases where a modem link is free of bit errors, the margin the modem receiver has for bit errors can be determined). Testloop 3, as dened in the Recommendation T/CD 01-01, will be available and can be controlled both manually and through the interface (circuit 14
14、1). Facilities shall be included to distinguish, without external equipment, between incorrect operation of the modem and failures of the telephone-line. A 5 11 bit pseudo random generator and detector shall be incorporated. An error indicator will flash for 0.5 second each time an incorrect bit is
15、received. (The error detection will be such that receiving continuous O or continuous 1 bits, will light the indicator.) CONSTRUCTION Means shall be provided for suitability in a 600 mm and 19 inch rack. For further requirements: see Recommendation T/CD 01-0 1. POWER SUPPLY See Recommendation T/CD 0
16、1-01. ENVIRONMENTAL REQUIREMENTS See Recommendation T/CD 01-01. Edition of November 30, 1985 CEPT T/CD*OII-OY*E 79 W 2326qIIq 00030YY II = T/CD O1 -04 E Page 10 Section B. No requirements. National network dependent reqiiirenients Section C. Optional requirements 1. GENERAL Together with Section A,
17、a modem for 2-wire operation OS 4-wire operation can be formed, depending on the options chosen. 2. DATA SIGNALLING RATES In Section A. 3. INTERFACES 3.1. DTE-DCE interface (interchange circuits) 3.1.1. The list of interchange circuits essential for the modem is given in Table 1. Interchange circuit
18、 No. Designation 1 o2 103 Transmitted data 104 Received data Signal ground or common return 105 Request to send 106 Ready for sending 107 Data set ready lOS/l or 108/2 Data terminal ready (see Note 1) 109 111 Connect data set to line Data channel received line signal detector Data signalling rate se
19、lector (DTE source) 113 114 115 Transmitter signal element timing (DTE source) Transmitter signal element timing (DTE source) Receiver signal element timing (DTE source) 118 119 120 121 122 125 Transmitted backward channel data Received backward channel data Transmit backward channel line signal Bac
20、kward channel ready Backward channel received line signal detector Calling indicator 140 141 142 Test indicator Loop back/maintenance test (Note 3) Local loop back (Note 3) 2-wire operation i X X X X X X X X + X X 4-wire operation X X X X x X X X X Note 1: Note 2: Note 3: This circuit shall be capab
21、le of operation as circuit lOS/l or circuit 108/2 depending on its use. For automatic calling it shall be used as 108/2 only. The functional characteristics of the interchange circuits are defined in the Recommendation T/CD 01-01. Loop back procedures are subject of urgent study. Edition of November
22、 30, 1985 CEPT T/CD*OL-O4*E 79 = 2326434 0003045 3 _ _ - greater than X dBm circuits 109 ON - less than Y dBm circuits 109 OFF T/CD O1 -04 E Page 12 value of: 2-wire mode X -43 -33 -26 Y 48 -38 -3 1 3.1.2. 3.1.3. The electrical characteristics of the interchange circuits are given in the Recommendat
23、ion T/CD 01-01. Response times of circuits 106 and 109 (see Table 2). DeJinition i) Dibit In order to achieve that the modulation rate is half the data signalling rate, two consecutive bits are encoded together. These hvo consecutive bits are called a dibit. For the whole duration of the interval be
24、tween the OFF to ON transitions of circuits 105 or 107 and 106, the line signal shall be that corresponding to the continuous transmission of dibit 11. This shall be known as the synchronizing signal. iii) Circuit 109 response times are the times that elapse between the connection or removal of the
25、test synchronizing signal to or from the modem receive line terminals and the appearance of the correspond- ing ON and OFF condition on circuit 109. The level of the test synchronizing signal should fall within the level range between 3 dB above the actual OFF to ON threshold of the received line si
26、gnal detector and the maximum admissible level of the received signal. At all levels within this range, the measured response times shall be within the specified limits. iv) Circuit 106 response times are from the connection to an ON or OFF condition on: - circuit 105 to the appearance of the corres
27、ponding ON or OFF condition on circuit 106; or - circuit 107 (where circuit 105 is not required to initiate the synchronizing signal) to the appearance ii) Synchronizing signal of the Corresponding ON of OFF condition on circuit 106. Circuit 106 OFF to ON ON to OFF Circuit 109 OFF to ON ON to OFF 2-
28、wire operation II 4-wire operation I 750 ms to 1,400 ms 1 (a) 65 ms to 100 ms (see Note 1) (see Note 2) (b) 200 ms to 275 ms (see Note 2) 2 ms 65 ms to 100 ms (see Note 4) 25ms to 45ms (see Note 5) 2 ms 300 ms to 700 ms (see Note I) 5 ms to 15 ms (see Note 2) 11 10+5ms Il 5 ms to 15 ms (see Note 1)
29、(see Note I) I 5 ms to 15 ms Section C. Table 2. Response times. 4-wire mode The condition of circuit 109 for levels between X dBm and Y dBm is not specified except that the signal detector shall exhibit a hysteresis action such that the level at which the OFF to ON transition occurs is at least 2 d
30、B greater than that for the On to OFF transition. Edition of November 30, 1985 -=-_ CEPT T/CD*OL-OY*E 232bYl14 O003046 5 = T/CD 01-04 E Page 12 3.1.5. 3.1.6. 3.2. 3.3. 3.3.1. 3.3.2. 3.3.2.1. 4. 5. 6. 7. 7.1. 7.2. Clamping in hau-duplex The DCE, when operating in half-duplex mode on a two-wire line,
31、shall hold circuit 104 in the binary 1 condition and circuit 109 in the OFF condition when circuit 105 is in the ON condition and, to protect circuit 104 from false signals, for a period of X milliseconds following the ON to OFF transition on circuit 105. This time shall be selectable: X = 150f25 or
32、 60f 10. Fault condition of interchange circuits (See the Recommendation T/CD 01-01 for association of the receiver failure detection types.) (a) The DTE should interprete a fault condition on circuit 107 as an OFF condition using failure detection type 1. (b) The DCE should interprete a fault condi
33、tion on circuits 105 and 108 as an OFF condition using failure detection type 1. (c) All other circuits not referred to above may use failure detection types O or 1. Telephone line interface The requirements are listed in the Recommendation T/CD 01-01. Automatic answering Automatic answering will be
34、 provided in conformity with the Recommendation T/CD O1 -01. Automatic disconnection This disconnection is made within 20 seconds, if the following condition applies: (a) circuit 109 is in the OFF condition for more than 150 ms. (b) circuit 122 is in the OFF condition for more than 150 ms. MODULATIO
35、N AND CODING In Section A. SCRAMBLING A self svnchronizing scrambler/descrambler shall be included in the modem. The scrambleridescrambler operatiin can be tuked off (by-passed) by means of a switch. TIMING In Section A. BACKWARD CHANNEL Modulation rate and characteristic frequencies for the backwar
36、d channel The modulation rate and characteristic frequencies for the backward channel are as follows: Fz F* (symbol 1, mark) (symbol O, space) Modulation rate up to 75 baud 390 Hz 450 Hz In the absence of any signal on the backward channel interface, the condition Z signal is to be Tolerances on the
37、 characteristic frequencies of the backward channel ran mitted. As the backward channel is a VF telegraph-type channel, the frequency tolerances should be as recommen- ded in Recommendation R.35 for frequency-shift voice-frequency telegraphy. The f 6 Hz frequency drift in the connection between the
38、modems would produce additional distortion in the backward channel. This should be taken into account in the design. Edition of November 30, 1985 CEPT T/CD*OL-O4*E 232b414 0003047 7 7.3. 7.3.1. 7.3.2. 7.3.3. 7.3.4. 7.4. T/CD O1 -04 E Page 13 Interchange circuits The associated interchange circuits a
39、re: 1 18 Transmitted backward channel data. 119 Received backward channel data. 120 Transmit backward channel line signal. 121 Backward channel ready. 122 Backward channel received line signal detector. The functions and electrical characteristics of these interchange circuits are defined in the Rec
40、om- mendation T/CD 01-01. Threshold of backward channel received line signal detector Level of received line signal at receive line terminals of modem: - greater than -43 dBm - less than 43 dBm The condition of circuit 122 for levels between -43 dBm and -48 dBm is not specified except that the signa
41、l detectors shall exhibit a hysteresis action such that the level at which the OFF to ON transition occurs is at least 2 dB greater than that for the ON to OFF transition. By means of a strap, these response levels can be changed to less sensitive valves: -33 dBm and -38 dBm respectively. Response t
42、imes of circuits 121 und 122 Circuit 121 OFF to ON 80 ms to 160 ms; ON to OFF 2 ms. Circuit 122 OFF to ON ON to OFF Clumping in half-duplex mode The DCE, when operating in half-duplex mode on a two-wire line, shall hold circuit 119 in binary 1 condition and circuit 122 in the OFF condition when circ
43、uit 120 is in the ON condition and, to protect circuit 119 from false signals, for a time interval of X milliseconds following the ON to OFF transition on circuit 120. This time shall be selectable: X = 150f25 or 80+ 15. circuit 122 ON. circuit 122 OFF. 80 ms; 15 ms to 80 ms. Division of power betwe
44、en forward and backward channels Equal division of power between forward and backward channels is recommended provisionally. Edition of November 30. 1985 CEPT T/CD*OL-O4*E D 2326439 00030Y8 9 T/CD O1 -04 E Page 14 8. 8.1. LINE SIGNAL CHARACTERISTICS Phase distortion limits The transmitted line signa
45、l spectrum should have linear phase characteristics (to be obtained by means of filters or equalizers or digital means). The deviation of this linear phase characteristic should not exceed the limits specified in Figure 1. 60“ LO 20 4 s 2 0 id c b - 20 -LO - 60 I 0, 6 1.0 1.L 1.e 2.2 2.6 Frequency (
46、f) I kHz a 0 a a Edition of November 30, 1985 Figure 1. Tolerance limit for phase distortion of the signal transmitted to the line. - 8.2. 9. 1 0. O 11. 12. 13. 14. 15. 16. 16.1. 16.2. CEPT T/CD*O1-04*E H 2326414 0003049 O D TICD O1 -04 E Page 15 Amplitude distortion limits The transmitted line sign
47、al spectrum shall have an amplitude within the limits of Figure 2. 2 2.6 3. kHz Frequency (0 Figure 2. Tolerance limit for amplitude characteristic of the signal transmitted to the line. Note: The values in Figure 2 are provisional. OUT-OF-BAND INTERFERENCE No additional requirements. PERFORMANCE RE
48、QUIREMENTS No additional requirements. TESTING AND MEASURING REQUIREMENTS Testloop 2 will be available. Loop 2 can be controlled both manually and via circuit 140 of the remote modem. The way this is achieved is subjected to further study. (Only possible for 4-wire operation.) 1 No additional requirements. 1 OTHER REQUIREMENTS Disabling of echo suppressors. This is specified in the Recommendation T/CD 01-01, Compromise equalizer inlout This switch by-passes the compromise equalizer. This switch is mounted inside the modem. Edition of November 30, 1985
