High-Level Data Link Control (HDLC)

High-Level Data Link Control (HDLC) is the encapsulation method used by serial links and is
the default on Cisco serial interfaces. The protocol provides for a 32-bit checksum and three
transfer modes: normal, asynchronous response, and asynchronous balanced. Many point-topoint
connections using Cisco routers continue to make use of the HDLC protocol.