The Common Channel Signaling System 7 is a set of application protocols for the transmission of service information over telephone networks.

SS7 is used for routing connections in digital or analogue voice-to-voice communication, and also facilitates the exchange of service data. It is also used for billing calls and for other purposes. The SS7 infrastructure forms the basis for services such as automatic number identification (ANI), call forwarding, and incoming call holding.

Developed in 1975, it falls short of today’s security requirements: various studies have highlighted SS7’s vulnerabilities, which can be exploited to eavesdrop conversations and determine caller location.