Description: Communication Channel (C-channel). C-paths (see v52CPathTable) are carried over C-channels (communications channels). In V5, there are two types of C-channels, logical and physical. Information about logical and physical C-channels is included in the provisioning data for V5.2 interfaces. A C-path associated with a logical C-channel is protected. A C-path associated with a physical C-channel is not protected.

In V5.2 only, logical C-channels carry a group of one or more C-paths, excluding the C-paths for the protection protocol. A logical C-channel may consist of the C-paths for the Control, Link Control, and BCC protocols. Another logical C-channel may consist of the C-path for the PSTN protocol. A third logical C-channel may consist of the C-paths for ISDN Ds-type data and ISDN p-type data. A V5.2 interface may contain up to 44 logical C-channels and each logical C-channel on an interface is uniquely identified in V5.2 with a 16-bit logical C-channel identifier.

The goal of the protection protocol is to protect the C-paths for the V5 Signaling protocols (ie, BCC, Control, etc) as well as the C-paths for ISDN D-channel data. However, the protection protocol is designed to protect logical C-channels, not C-paths. Therefore, in order to protect a C-path, it must be associated with a logical C-channel. This association is made as part of the provisioning variant.

A physical C-channel consists of a time slot (64kbit/s) on an E1 that carries a C-channel (C-channels are used to carry signaling traffic). All physical C-channels are restricted to timeslots 16, 15, and 31 in accordance with the ETSI specification.

If logical C-channels are in use, each logical C-channel is mapped to one and only one physical C-channel. This restriction is mandated by the role of the protection protocol. The protection protocol, which protects logical C-channels, can only protect a single logical C-channel per protection switch over. This implies an implicit limitation of one logical C-channel per physical C-channel.

For a V5.2 interface, the physical C-channels are identified by a logical link ID and a timeslot. Each V5.2 interface can support a maximum of 48 physical C-channels (timeslots 16, 15, and 31 on up to 16 E1 links; 3 * 16 = 48).

Physical C-channels are not available for bearer connections. The physical C-channels are identified at provisioning time and when ISDN ports with D-channel signaling are added.