Signaling System Number 7

Abstract

In a public switched telephone network (PSTN), the control information is exchanged among the network elements by signaling. The early telephone system used circuit associated signaling or inband signaling where the same transmission channel was shared by both signaling and user information (voice or data). Another signaling method is common channel signaling (CCS). Unlike the circuit associated signaling, CCS uses a separate out-of-band signaling network to carry signaling messages. CCS consists of supervisory functions, addressing, and providing call information. A CCS channel conveys messages to initiate and terminate calls, check on the status of some part of the network, and control the amount of traffic allowed. Signaling System No. 7 (SS7) is a CCS system developed to satisfy the telephone operating companies' requirements for an improvement to the earlier inband signaling systems. The advantages of CCS are listed.