The Signaling System 7 (SS7) is an international telecommunications protocol standard that specifies how network elements in a public switched telephone network (PSTN) exchange data and control signals.

It is the software that manages how phone calls are routed and invoiced, as well as sophisticated calling capabilities and SMS text messaging (SMS).

It is also known as Signalling System No. 7, Common Channel Signaling System 7, or CCSS7 in the United States.

The following are some of the services provided by SS7:

– Call setup, routing, and teardown
– Call forwarding
– Automated voicemail
– Call waiting
– Conference calling
– Caller ID
– Subscriber authentication, and extended billing
– Toll-free (800 and 888) and toll (900) calls toll-free (800 and 888) and toll (900) calls
– Roaming and monitoring of mobile phones