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.
The standard allows the existence of 1024 DLCIs. DLCI 0 reserved for ANSI/q993a LMI standard - only numbers 16 to 976 are usable for end-user equipment. DLCI 1023 is reserved for Cisco LMI - however, the numbers usable are from 16 to 1007.
In summary, only numbers from 16 to 1007 are available for end users' equipment (If using Cisco LMI). The rest are reserved for various management purposes. 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.