In the integrated service digital network (ISDN), a channel designated for out-of-band signaling and control functions. Standard ISDN interfaces include multiple B (Bearer) channels that carry user payload and a D channel for signaling and control. Basic rate interface (BRI) comprises two B channels at 64 kbps and one D channel at 16 kbps, and is often referred to as 2B+D. Primary rate interface (PRI) comprises 23 B channels at 64 kbps, plus a D channel at 64 kbps, is compatible with North American T1 and Japanese J-1 standards, and is often referred to as 23B+D. Primary rate access (PRA) comprises 30 B channels at 64 kbps, plus a D channel at 64 kbps, is compatible with European E-1 standards, and is often referred to as 30B+D. A D channel also can support low-speed end user packet data and telemetry applications. See also D, B channel, BRI, E-1, ISDN, J-1, packet, payload, PRA, PRI, and T1.