High-Level Data-Link Ascendancy (HDLC)
Protocol
HDLC is a accepted ISO-standard, bit-oriented, Abstracts Link band protocol. It specifies an encapsulation
method for abstracts on ancillary consecutive abstracts links application anatomy characters and checksums.
HDLC is a point-to-point agreement acclimated on busy lines. No affidavit can be used
with HDLC.
In
byte-oriented protocols
, ascendancy advice is encoded application absolute bytes. On the other
hand,
bit-oriented protocols
use distinct $.25 to represent the ascendancy information. Some common
bit-oriented protocols accommodate SDLC, LLC, HDLC, TCP, and IP.
HDLC is the absence encapsulation acclimated by Cisco routers over ancillary consecutive links.
And Cisco’s HDLC is proprietary—it won’t acquaint with any added vendor’s HDLC
implementation. But don’t accord Cisco affliction for it—
everyone’s
HDLC accomplishing is proprietary.
Figure 11.1 shows the Cisco HDLC format.
As apparent in the figure, the acumen that every bell-ringer has a proprietary HDLC encapsulation
method is that anniversary bell-ringer has a altered way for the HDLC agreement to abbreviate multiple
Network band protocols. If the vendors didn’t accept a way for HDLC to acquaint the different
layer-3 protocols, again HDLC would be able to backpack alone one protocol. This proprietary
header is placed in the abstracts acreage of the HDLC encapsulation.