Common channel signaling

Common channel signaling protocols, such as Signaling System 7 (SS7) or ISDN, carry all the signaling information for many voice channels over a single, dedicated signaling link. The common channel signaling link can provide:

• Call setup and clearing
• Detection and notification of caller hangup (far-end hangup)
• Provision of call information, such as the caller’s telephone number
• PABX-like functions, such as call transfer and message waiting indication

The signaling link is usually one or more 64Kbps channels on a T1 or E1 trunk. Most common channel signaling protocols are based on the OSI reference model (X.200), and work by exchanging predefined messages.

Common channel signaling is not used in conjunction with exchange data links or channel associated signaling protocols.