CCNA Cisco Certified Network Associate Study Guide - FTP Server

High-Level Data-Link Control Protocol (HDLC) 481
LAPB Link Access Procedure, Balanced was created to be used as a connection-oriented
protocol at the Data Link layer for use with X.25. It can
also be used as a simple Data Link transport. LAPB has a tremendous
amount of overhead because of its strict timeout and windowing techniques.
You can use LAPB instead of the lower-overhead HDLC if your
link is very error prone. However, that typically is not a problem any
longer.
HDLC High-Level Data Link Control was derived from Synchronous
Data Link Control (SDLC), which was created by IBM as a Data Link
connection protocol. HDLC is a connection-oriented protocol at the Data
Link layer, but it has very little overhead compared to LAPB. HDLC was
not intended to encapsulate multiple Network layer protocols across the
same link. The HDLC header carries no identification of the type of protocol
being carried inside the HDLC encapsulation. Because of this, each
vendor that uses HDLC has their own way of identifying the Network
layer protocol, which means that each vendor’s HDLC is proprietary for
their equipment.
PPP Point-to-Point Protocol is an industry-standard protocol. Because
many versions of HDLC are proprietary, PPP can be used to create pointto-point
links between different vendors’ equipment. It uses a Network
Control Protocol field in the Data Link header to identify the Network
layer protocol. It allows authentication and multilink connections and
can be run over asynchronous and synchronous links.
High-Level Data-Link Control
Protocol (HDLC)
The High-Level Data-Link Control protocol (HDLC) is a popular ISOstandard,
bit-oriented Data Link layer protocol. It specifies an encapsulation
method for data on synchronous serial data links using frame characters and
checksums. HDLC is a point-to-point protocol used on leased lines. No
authentication can be used with HDLC.