Signaling Protocols

When you need to connect to a telephone outside of your switch, and certainly when you need to connect to one outside of your region, the public switched telephone network (PSTN) uses the Signaling System 7 (SS7) switching standard that was developed in 1981 by the ITU-T, formerly known as the CCITT. SS7 is an out-of-band signaling architecture. This architecture means that the signals are sent in a different frequency range than the voice data. It can also mean that the signals are sent on a different wire than the voice data. In-band signaling, like local loop signaling, is actually sent using the limited available bandwidth in the channel. In the case of the SS7 system, a separate line is used or an entirely separate network is used.