Common Data Link (CDL) is a secure U.S. military communications protocol. It was established by the U.S. Department of Defense in 1991 as the military's primary protocol for imagery and signals intelligence. CDL operates within the Ku band at data rates up to 274 Mbit/s. CDL allows for full duplex data exchange. CDL signals are transmitted, received, synchronized, routed, and simulated by Common data link (CDL) Interface Boxes (CIBs).