The signalling problems associated with register-controlled automatic telephone exchanges

Subscriber trunk dialling requires routing to be divorced from numbering. The paper discusses the various signalling problems which arise with register-translators. Basic principles are analysed rather than details of design, and a signalling philosophy is formulated as a basis of design for national and international networks. A main problem is the choice between the same or separate line equipment for the supervisory and number signalling; the paper details the merit of supervisory signalling by per-line equipment and number signalling by common-register equipment. End-to-end and link-by-link signalling, the signalling facilities to be given and the number signalling code all influence the signalling technique, and are analysed. Conclusions are given on the merits of link-by-link line signalling for flexibility of application, of end-to-end register number signalling for fast call set-up time and short post-dialling delays, and of fast coded self-checking multi-frequency signals for number transmission. The transmission features of line networks will have considerable influence on signalling-system design, particularly with end-to-end signalling for number transmission. Satisfactory design solutions are possible with limited end-to-end signalling. Speech-interpolation equipment (t.a.s.i.) applied to intercontinental circuits modifies the conclusions reached for the non-t.a.s.i. condition if account is to be taken of minimum degradation of the t.a.s.i. advantage, and the basic problem is the relative assessment of call set-up time and t.a.s.i.-advantage considerations.