D channel

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D channel (delta channel) is a telecommunications term which refers to the ISDN channel in which the control and signalling information is carried.{{Cite web |last=Team |first=Editorial |date=2019-09-03 |title=D Channel: The Backbone of ISDN Signaling |url=https://networkencyclopedia.com/d-channel/ |access-date=2024-10-10 |website=NETWORK ENCYCLOPEDIA |language=en-US}}

The bit rate of the D channel of a basic rate interface is 16 kbit/s, whereas it amounts to 64 kbit/s on a primary rate interface.

For DSS1 signalling, the D channel layer 2 protocol is Q.921 also called LAPD and it carries Layer 3 messages according to Q.931 protocol.