A set of telephony signaling protocols developed in the 1970s, Signaling System 7 (SS7) is used to setup and teardown telephone calls on most parts of the global public switched telephone network (PSTN). The protocol also performs number translation, local number portability, prepaid billing, Short Message Service (SMS), and other services.
Telephony Applications
SS7 handles various telephony applications including call setup, routing, and teardown. It enables advanced services like caller ID, call forwarding, and conference calling.
- Call setup: Initiates and manages the connection between calling and called parties.
- Call routing: Determines the most efficient path for the call through the network.
- Call teardown: Terminates the connection once the call is completed.
International Standards
The SS7 protocol is defined for international use by the Q.700-series recommendations of 1988 by the ITU-T. It is based on variants standardized by the American National Standards Institute (ANSI) and the European Telecommunications Standards Institute (ETSI).
Historical Context
The protocol was introduced in the Bell System in the United States by the name Common Channel Interoffice Signaling in the 1970s for signaling between No. 4ESS switch and No. 4A crossbar toll offices.