Common Channel Interoffice Signaling: An Overview

An Overview By A. E. Ritchie and J. Z. Menard (Manuscript received May 7, 1977) In May of 1976, a new Common Channel Interoffice Signaling (CCIS) system linked together the last new No. 4A toll crossbar office in Madison, Wisconsin and the first No. 4 ESS toll office in Chicago, Illinois. This was a major milestone in a long-range program to achieve a nationwide Stored-Program Controlled (SPC) network of stored-program controlled switching offices interconnected by a new high-speed, high-capacity interoffice signaling system, CCIS. The SPC network will provide faster, more reliable communications and will make possible a myriad of new communication services. An evolutionary transition to the SPC network is in progress. CCIS is now being implemented in the toll or long-distance network. It will subsequently be extended to Traffic Service Position System (TSPS) units and to Electronic Switching System (ESS) local switching offices to provide customer-to-customer CCIS service. This issue of the Bell System Technical Journal is devoted to CCIS. This overview and the following articles cover the inception and goals of the program and the implementation of CCIS in the toll network. In telephony, interoffice signaling has two functionally different components: supervisory signaling, used to initiate and terminate connections, and to indicate call status; and address or control signaling, used to communicate the destination of a call. Supervisory signaling 221 requires two-way communication, and address signaling is usually restricted to one-way forward operation.