Summary

             Signalling System No. 6 could be used to control the switching of all types of international circuits, including TASI-derived circuits and satellite circuits. It is designed for both-way operation of the speech circuits. The system can also be used for regional and national applications, and a large part of the signal code capacity is reserved for this purpose.

             The system features are obtained by entirely removing the signalling from the speech paths and introducing the concept of a separate common signalling link over which all signals for a number of speech circuits are transferred. A number of these common signalling links interconnected by a number of transit centres and signal transfer points will form a coherent signalling network which can transfer all signals for all speech circuit groups within that network area.

             The separate common signalling link is capable of operation over both analogue and digital circuits. Signalling information is transmitted in the serial data mode on a link-by-link basis – i.e. the signals are transferred from one link to the next only after processing.