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

  1. What is HDLC?
  2. Different HDLC Stations
  3. HDLC Transfer Models
  4. 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

  1. Primary Station

    • Manages the establishment and de-establishment of data channels.
    • Shares frames in the network (commands) and performs data management.
  2. Secondary Station

    • Operates under the command of the primary station.
    • Frames issued are known as responses.
  3. Combined Station

    • Functions for both commands and responses.

HDLC Transfer Models

  • HDLC supports two transfer models based on communication needs:
    1. Normal Response Model (NRM)
      • Combines primary and secondary stations in point-to-point or multipoint configurations for command-response exchange.
    2. 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:
    1. Flag Field
      • Starts each frame with an 8-bit octet sequence: 01111110.
    2. Address Field
      • Contains the receiver's address (e.g., secondary station's address if sent from the primary station).
    3. Control Field
      • Contains flow and error control information.
    4. Payload/Information Field
      • Carries actual information from the upper OSI layer.
    5. 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:
    1. I-frame (Information Frame)
      • Encapsulates user information from the upper layer.
      • Control field's first bit is always 0.
    2. 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.
    3. 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.