SS7 (Signaling System 7) is a standard for control signaling in the PSTN (Public Switched Telephone Network.
SS7 signaling is done out-of-band, meaning that SS7 signaling messages are transported over a separate data connection. This represents a significant security improvement over earlier systems which used in-band signaling.
SS7 is referred to by many other names, including CCS7 (Common Channel Signaling System 7), C7, Number 7, and CCIS7 (Common Channel Interoffice Signaling 7).
SS7 Tutorials
To learn more about SS7, explore one of these fine SS7 tutorials: