ITU-T Q.45 BIS PDF

General

The concern of this Recommendation is the transmission performance of an analogue international exchange in terms of design objectives [1]. Related commissioning objectives [1] may be based on this Recommendation.

For the purposes of this Recommendation an analogue international exchange is a collection of equipment regarded as an entity by the Administration concerned. In the case of an analogue international transit exchange, it extends from the end of the incoming international line (point A of Figure 1/Q.45 bis) to the beginning of the outgoing international line (point D of Figure 1/Q.45 bis).

Exchange testing uses measuring points at boundaries of the same exchange individually agreed upon.

In contrast to exchange testing, circuit testing [2] is recommended between circuit access points expected to be located at or near by the actual analogue switching points (points B or C of Figure 1/Q.45 bis). For the purpose of circuit line-up and maintenance procedures, automatic international exchanges should be provided with circuit test access points.

Applying this Recommendation due account should be taken to the different constitution of the section of transmission under test compared to circuit testing [2].

The essential transmission requirements for an international exchange are:

a) The transmission loss through the exchange should be substantially constant with time and independent of the routing through the exchange.

b) Crosstalk and noise contribution should be negligible compared with other transmission sections in a world-wide connection [3].

c) The distortion introduced should be small. These include attenuation distortion, non-linear distortion and intermodulation products.

d) Impedance and balance with respect to earth at the points in the international exchange to which the lines are connected should be closely controlled.

This Recommendation applies to analogue automatic 4-wire international exchanges. It is desirable that it should also apply to analogue national 4-wire exchanges.

The following requirements are intended to be used only for type tests, acceptance tests, or for special investigations. They do not constitute a complete specification. Generally the recommended tests should be conducted on a sampling basis.