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Difference between CAS and CCS

This page CAS vs CCS describes CAS(Channel Associated Signaling),CCS(Common Channel Signaling) and mentions comparison or difference between CAS and CCS techniques.


In CAS, signaling is sent over the same channel over which voice calls are carried.

PCM signaling is one of the technique used as CAS in which signaling frame samples are transmitted well within the channel dedicated for PCM frame.


PCM T1 frame

In CCS, signaling is sent over the different separate channel other than the channel over which voice calls are carried. CCS is widely employed across the world in all the telephone exchanges and betweeen exchanges(PBXs). CCS usually requires only one signalling channel for upto about 1000 traffic channels.

PCM signaling can also be used as CCS. In 30 channel case, time slot number 16 is used as common signaling channel. The rate for the channel is about 64kbps. In 24 channel case, 193rd bit can be used alternately in the PCM frames to carry signaling information at the rate of about 4kbps.

To understand difference between CAS and CCS, any switching guy must understand concepts of PCM (Pulse code modulation) and its frame structure.

Also refer Difference between T1-frame and E1-frame used in PCM systems➤➤.

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