The 81-a exchange trunk carrier system ¿ Signaling

This paper describes the unique time-division-multiplex supervisory and signaling system employed in the 81-A Exchange Trunk Carrier, the general features of which are covered in a companion paper by M. E. Ferguson and M. C. Harp in this issue. In the design of carrier systems, a problem requiring almost as much effort as that of the transmission of conversations is that of the transmission of signaling information. In fact, considering the wealth of options and varieties of signaling encountered in exchange carrier service, one laboratory wag has described exchange carrier equipment as ¿a collection of signaling gear with incidental talking channels.¿ And, indeed, in exchange carrier design, the variety of signaling requirements encountered is almost without end.