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Collaboration, Voice & AV · Intermediate

Common Channel Signaling (CCS)

Signaling sent on a separate dedicated channel shared by all bearer channels, such as the ISDN D channel or SS7.

Definition

CCS separates call control from voice by placing signaling messages for many calls in a single channel. ISDN PRI and BRI use a D channel running Q.931, and carriers use SS7 between switches. CCS enables faster setup and richer features such as calling name, redirecting number and message-oriented signaling.

Example

A PRI D channel on timeslot 24 carries Q.931 SETUP and CONNECT messages for all 23 bearer channels.

Exam tip

Exam distractors often swap CAS and CCS; CCS is out-of-band in a separate channel.

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