Stored Program Controlled Network: CCIS and SPC Network Performance

Common-channel interoffice signaling (ccis) was introduced to provide the advantages of greater economy, faster call setup, improved security from fraud, and improved flexibility. The initial ccis implementation was limited to class 1 to class 4 toll offices, but was extended to class 5 end offices during 1981. Several companion articles provide detailed accounts of ccis implementation and describe its characteristics. At year-end 1981, over 160 toll switching offices were interconnected through the ccis network, which then comprised 24 signal transfer points (STPS) and signaling links serving over 400,000 trunks. The signaling link consists of an analog voice bandwidth channel with a ccis terminal at each end. These links currently operate at a data rate of 2400 b/second. Because of the increasing traffic in the network, higher-speed links (4800 b/s) are being introduced. 1637 Supervisory and address signaling information for a conventional call is usually transmitted directly from one switching system to the next over the same communication channel used for talking. A ccis call, on the other hand, uses the separate, duplicated, signaling network to carry its supervisory and address signaling information. Since ccisequipped switching offices access the signaling network through a pair of STPS, signaling for a trunk between two ccis switching offices will typically be routed through one or two STPS and two or three signaling links, depending on whether the two switching offices are served by the same or different STP pairs.