Common Channel Signalling (CCS) is a signalling system in which the signalling information is transmitted separately from the user data. This out-of-band sign alling is used in many telephone networks
. For example, in ISDN, the signaling for the basic access and the primary multiplex access
iscarried over the separate D channel. In addition, central channel signaling is used in SS7 signaling
.Digital Private Network Signaling System (DPNSS) are also signaling systems that transmit signaling information separately. In contrast, Channel Associated Signalling (CAS) transmits the signalling information together with the user data. This signalling is also known as inner-band
Common Channel Signalling provides a relatively fast connection setup, it has short redial times, efficient routing and supports a wide variety of signalling.