A data link connection identifier (DLCI) is a Frame Relay 10-bit-wide link-local virtual circuit identifier used to assign frames to a specific PVC or SVC. Frame Relay networks use DLCIs to statistically multiplex frames. DLCIs are preloaded into each switch and act as road signs to the traveling frames.[1]
The standard allows the existence of 1024 DLCIs. DLCI 0 is reserved for the ANSI/q993a LMI standard—only numbers 16 to 976 are usable for end-user equipment. DLCI 1023 is reserved for Cisco LMI, however, numbers 16 to 1007 are usable.[2]
In summary, if using Cisco LMI, numbers from 16 to 1007 are available for end-user equipment. The rest are reserved for various management purposes.[3] DLCI are Layer 2 Addresses that are locally significant. No two devices have the same DLCI mapped to its interface in one frame relay cloud.