The Picturephone System: Switching Plan

A prime objective of Picturephone service is to make it a natural extension of present telephone service. T h e switching plan gives explicit definition to this objective while permitting extensive use of the portion of the switching plant t h a t performs functions common to both services. Where economies dictate t h a t the Picturephone network depart from the telephone network, the switching plan provides the means. T h e technical aspects of switching and transmitting a video signal are treated in other articles in this issue. This paper deals primarily with the service as seen by the customer, and about those engineering factors which then follow from the sendee definition. I I . OPERATING PROCEDURES The operating procedures for Picturephone service form a set of self-consistent rules which define it as a vertical extension of telephone service. From these procedures, requirements are generated for the switching hardware to provide the customer, local, and toll switching for the service. These procedures are as follows: (i) Picturephone and telephone calls are placed and received on common station equipment. (it) The telephone loop carries Picturephone audio. (iii) The telephone line is busy when a Picturephone call is in progress and vice versa. (iv) Picturephone and telephone numbers are the same. 521