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Overview of HDLC Protocol Features
Sep 25, 2024
HDLC Protocol Overview
Introduction
HDLC (High-Level Data Link Control) protocols are essential for efficient and secure data exchange across network channels.
This lecture by SimpliLan covers key aspects of HDLC.
Agenda
What is HDLC?
Different HDLC Stations
HDLC Transfer Models
HDLC Frame Model and Types
What is HDLC?
HDLC is a bit-oriented network protocol designed for connecting multiple network systems.
It uses the ARQ protocol for applications and establishes full duplex communication between devices.
Types of HDLC Stations
Primary Station
Manages the establishment and de-establishment of data channels.
Shares frames in the network (commands) and performs data management.
Secondary Station
Operates under the command of the primary station.
Frames issued are known as responses.
Combined Station
Functions for both commands and responses.
HDLC Transfer Models
HDLC supports two transfer models based on communication needs:
Normal Response Model (NRM)
Combines primary and secondary stations in point-to-point or multipoint configurations for command-response exchange.
Asynchronous Balanced Model
Utilizes combined stations in point-to-point configurations for command and response exchange from either node.
HDLC Frame Model and Types
HDLC frames are essential for information sharing and consist of five fields:
Flag Field
Starts each frame with an 8-bit octet sequence:
01111110
.
Address Field
Contains the receiver's address (e.g., secondary station's address if sent from the primary station).
Control Field
Contains flow and error control information.
Payload/Information Field
Carries actual information from the upper OSI layer.
FCS Field (Frame Check Sequence)
Acts as an error detection field, includes a 6-bit CRC check.
Frame Format
Frame format: Flag Field -> Address Field -> Control Field -> Information Field -> FCS Field.
Quiz Question
The HDLC protocol functions under which OSI layer?
Options:
Application Layer
Data Link Layer
Physical Layer
Network Layer
Types of Frame Models in HDLC
Frame models classified based on the control field value:
I-frame (Information Frame)
Encapsulates user information from the upper layer.
Control field's first bit is always 0.
S-frame (Supervisory Frame)
Used for error and data flow control.
Does not contain information field.
Control field's first two bits are 1 and 0.
U-frame (Unnumbered Frame)
Used for system management and exchanging information between network devices.
Conclusion
Covered essential information regarding the HDLC protocol.
Questions can be asked in the comment section.
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Full transcript