Common Channel Interoffice Signaling: History and Description of a New Signaling System

Until now signaling systems have to a large extent been provided on a per trunk in-band basis and generally have provided adequate performance for the present-day operating environment. The limitations of the systems have been enumerated in the lead article, and these together with the requirements for higher-speed signaling and vastly expanded signal capacity have led to the introduction of common channel signaling systems for both domestic and international telephone systems. The concept of common channel signaling is not new but only recently have advances in technology made it possible for large-scale imple225 mentation of such systems. As a result, new customer services and sophisticated network controls requiring additional signals become possible, all with complete independence between the transmission channel used by the customer and the channel used for signaling.