The HDLC Address Field

The first byte(s) of a frame transmitted using the High Level Link Control (HDLC) Protocol areused to carry an address field. This field is typically a single byte, but extension is possible allowing a number of bytes to be used. The address format is shown in the figure below.

Format of the Address Byte(s) in HDLC

The address consists of three parts:

The address field is mainly used when HDLC is used in a mode which provides reliable data transfer using numbered control frames.