ITU-T SERIES G SUPP 29-1993 混合模拟规划设计.数字电路(链、连接件).传输系统和介质.国际电话连接件和国际电话电路的一般特征.补充件29
Planning of Mixed Ananlogue - Digital Circuits (Chains, Connections) - Transmission Systems and Media - General Characteristics of International Telephone Connections and International Telephone Circuits Supplement 29
In the period of transition from a fully analogue to a fully digital network, mixed analogue-digital circuits, chains and
connections will take place on international and national networks for a fairly prolonged time.
The definition of notions of “mixed circuits, chains and connections” and examples of their possible structures are given
in Annex A.
Structure of mixed circuits and moreover that of connections and chains, may be highly complex in comparison with
circuits, chains and connections composed of transmission systems of one type (analogue or digital), that is, of
homogeneous structure. The most favourable from the point of view of minimization of analogue-digital conversions is
“overlay” strategy. Distortions and noise in mixed circuits to a great extent differ from those in circuits of the
homogeneous structure, because in the case of mixed circuits distortions and noise typical for both analogue and digital
transmission systems are combined taking into account the influence made on them by analogue-digital conversions.
Measuring methods for distortions and noise in mixed circuits are of specific character as well. Factors mentioned above
make the maintenance and operation of mixed circuits more complicated. Thus the task of developing planning rules for
mixed circuits (chains, connections) becomes actual as well as studying the addition laws for distortions and noise.