ITU-T Recommendation G.221 International analogue carrier systems. General characteristics common to all analogue carrier-transmission systems. Overall recommendations relating to carrier-transmission systems Международные аналоговые системы передачи. Общие характеристики, общие для всех аналоговых систем передачи. Общие рекомендации по системам передачи

INTERNATIONAL TELECOMMUNICATION UNION

ITU-T

TELECOMMUNICATION

STANDARDIZATION SECTOR

OF ITU

INTERNATIONAL ANALOGUE CARRIER SYSTEMS

GENERAL CHARACTERISTICS COMMON TO ALL ANALOGUE CARRIER-TRANSMISSION SYSTEMS

OVERALL RECOMMENDATIONS RELATING TO CARRIER-TRANSMISSION SYSTEMS

ITU-T Recommendation G.221

(Extract from the Blue Book)

NOTES

1 ITU-T Recommendation G.221 was published in Fascicle III.2 of the Blue Book. This file is an extract from the Blue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, the contents of the file are identical to die Blue Book version and copyright conditions remain unchanged (see below).

2 In this Recommendation, the expression “Administration" is used for conciseness to indicate both a telecommunication administration and a recognized opcrating agency.

© ITU 1988. 1993

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Recommendation G.221

OVERALL RECOMMENDATIONS RELATING TO CARRIER-TRANSMISSION SYSTEMS

(amended at Geneva, 1972 and 1980)

I Characteristics of complete circuits

The characteristics of complete circuits, measured between audio-frequency terminals (overall loss in terminal service and in transit service, frequency hands effectively transmitted and attenuation distortion, variation of overall loss with time, phase distortion, stability, crosstalk, etc.) should meet the general conditions for 4-wire telephone circuits indicated in Section 1 of the Scries G Recommendations.

• Linear crosstalk
  • Overall requirements

The requirements as regards crosstalk ratio between circuits in the case of telephony are the subjects of Recommendation G. 134 |l| and the Recommendation cited in |2|; for go-to-return crosstalk the Recommendation cited in [3] applies.

As carrier transmission systems are also used for setting up sound-programme circuits, the relevant requirements given in the Scries J Recommendations should be taken into consideration. Recommendation J. 18 |4| gives general guidance on how the higher crosstalk ratios appropriate to sound-programme transmissions are achieved in a telephone network.

In any case the near-end crosstalk ratio between the two directions of transmission at all frequencies used for the regulating and measuring pilots on earner systems should be not less than 40 dB.

• intelligible crosstalk caused by intermodulation with a signal which is a multiple of 4 kHz

Intelligible crosstalk may arise between circuits by way of intermodulation with a signal which is a multiple of 4 kHz, e.g. a line-regulating pilot. A design objective is that the intelligible crosstalk ratio in a single homogeneous section of the appropriate hypothetical reference circuit should be not less than 74 dB.