This section describes the VCI usage within an ATM cell. The reserved numbers of VCIs are shown in Figure B-7.
In the 65,536 possible virtual channels in each of the 256 virtual paths on any given UNI interface, there are 32 reserved virtual channel numbers. Those are VCIs 0 to 31. Some of these channels are still undefined and are left for future use. Some of the reserved VCIs are critical to the ATM network.
Here are the key virtual channels that are used for various types of signaling across the UNI or NNI:
Call signaling (frequently called VPI 0/VCI 5)— This is ...