The GR-303 CRV Table. The GR-303-CORE interface uses the Call Reference Value (CRV) in its Timeslot Management Channel (TMC) to dynamically assign DS0s to access circuits on a call-by-call basis; i.e., if an access circuit is not assigned a CRV, it will never be assigned a DS0 between the IDT and IG. The maximum number of entries is specified by the maximum number of subscribers or CRVs for the Interface Group, which is 2048. Each Interface Group is associated with an igCrvTable indexed by (shelf, slot, IG name, CRV). GR-303-CORE R12-508 [1377] The RDT is limited to a maximum of 28 DS1s per IG and each IG can support up to a maximum of 2048 two-wire terminations toward the customer's premises.