HDLC (High-Level Data Link Control)
Cisco’s default encapsulation type for serial interfaces, HDLC is used to encapsulate packets into frames over established, dedicated, point-to-point leased lines. HDLC packets are small and use low overhead, thus making
them quite efficient. HDLC also verifies link integrity and communications by implementing keepalives and sequence numbering. A downside of HDLC is that it provides no means for authentication.
HDLC encapsulation is the default assignment for serial interfaces.HDLC links are set up using two main types of network configurations:
Point-to-point: one to one
Multipoint: one to many
Router(config-if)#clock rate 64000