Integrated Digital Loop Carrier (IDLC) is required when a Digital Loop Carrier (DLC) system is integrated into a local digital link. The link access procedure on the D Channel for ISDN LAPD is the basis for the call processing and operations data-link layer protocol of the IDLC interface. The IDLC is above the LAPD protocol. DLC carries traffic for regular phone lines and integrated services digital network (ISDN) services.