ITU-T G 791-1988 General Considerations on Transmultiplexing Equipments - General Aspects of Digital Transmission Systems Terminal Equipments (Study Groups XV and XVIII) 2 pp《传输复用转.pdf

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1、CCITT FASCICLE 111.4 89 W 486259L 0503762 4 W 7.9 Other terminal equipments Recommendation G.791 GENERAL CONSIDERATIONS ON TRANSMULTIPLEXING EQUIPMENTS (Geneva, 1980; further amended) The CCIIPT, considering from FDM signals to TDM signals and vice versa, the advantages offered in some cases by dire

2、ct through-connection (without voice-frequency interfaces) recommends in such cases (1) the use of the transmultiplexing equipment described in Definition 4020 of Recommendation G.701; (2) Recommendation G.792 which contains the characteristics common to all transmultiplexing equip- ment; (3) Recomm

3、endation G.793 which concerns 60-channel transmultiplexers providing 2048 kbit/s signals (4) Recommendation G.794 which concerns 24-channel transmultiplexers providing 1544 kbit/s signals and using A-law encoding; and using plaw encoding. 1 Complementary definitions 1.1 type P transmultiplexer (TMUX

4、-P) A transmultiplexing equipment in which the analogue interface is made up of several groups. 1.2 type S transmultiplexer (TMUX-S) A transmultiplexing equipment in which the analogue interface is made up of one or more supergroups. 1.3 hierarchical transmultiplexer A transmultiplexer in which the

5、digital interfaces satisfy the provisions of Recommendations G.703 and G.704 and the analogue interfaces those of Recommendation G.233 i. 1.4 transmultiplexer channel A frequency band of 4000 Hz on the analogue side, corresponding to a bit rate of 64 kbit/s on the digital side, which permits the tra

6、nsmission of a signal limited to the telephone band 300-3400 Hz. Access may be gained to a given channel: - either at the level of the time slot associated with the relevant channel of the TDM signal; - or at the level of the frequency band (f, f, f 4000 Hz) of the FDM signal, fp being the virtual c

7、arrier frequency associated with the channel concerned. The + sign corresponds to the case of the base supergroup, the - sign to the case of the base group. Note - Correspondence between out-of-band signalling on the analogue side and channel associated signalling on the digital side will be covered

8、 in the Recommendations specific to the various transmultiplexers. 574 Fascicle 111.4 - Rec. 6.791 CCITT FASCICLE 111-4 89 4862593 0503763 6 = 2 Transmultiplexer application The application on transmultiplexers for the interconnection of digitaI and analogue networks is illustrated in Supplement No.

9、 28. Reference CCIT Recommendation Recommendations concerning translating equipments, Vol. III, Rec. G.233. i Recommendation G.792 CHARACTERISTICS COMMON TO ALL TRANSMULTIPLEXING EQUIPMENTS (Geneva, 1980; further amended) The CCIT, recommends dation G.791. that the characteristics below be respected

10、 by all the transmultiplexing equipments defined in Recommen- Recommendation 0.133 contains information about test equipment. Account should be taken of the measurement accuracy provided by test equipment designed in accordance with that Recommendation. The following specifications are based on idea

11、l measuring equipment. Therefore, they do not include any margin for measurement errors. To avoid level errors produced as a result of the use of test frequencies which are sub-multiples of the PCM sampling rate, the use of integer sub-multiples of 8 kHz should be avoided. Where a nominal reference

12、frequency of 1020 Hz is indicated (measurement of attenuation/frequency distortion and adjustment of relative levels), the actual frequency should be 1020, +2 to -7 Hz in accordance with Recommendation 0.6 18. 1 Coding law Transmultiplexers should satisfy Recommendation G.711, 0 3. 2 Sampling rate o

13、f PCM channels The nominal sampling rate of PCM channels is 8000 Hz f 50 lop6 according to Recommenda- tion G.711, 8 2. 3 Amplitude limitation of PCM channels In accordance with Recommendation G.711, 4 4, the theoretical load capacity of PCM channel is +3.14 dBmO for the A-law and +3.17 dBmO for the

14、 F-law. 4 Accuracy of the analogue virtual carriers The analogue virtual carriers should satisfy the Recommendation cited in i. 5 Saturation level at the input of the analogue group The transmultiplexers should be able to accept at their analogue inputs, levels corresponding to the equivalent peak powers defined in Table 3/G.223 5 (for example, + 19 dBmO for a group and + 20.8 dBmO for a supergroup). Fascicle 111.4 - Rec. G.792 575 -.