Computer Busses

I

HDLC

I.1 Introduction

The data link layer is the second layer in the OSI seven-layer model and its protocols define rules for the orderly exchange of data information between two adjacent nodes connected by a data link. Final framing, flow control between nodes, and error detection and correction are added at this layer. In previous chapters the data link layer was discussed in a practical manner. It is a use protocol as it provides a model for interfacing to a serial bus.

The two types of protocol are:

• Asynchronous protocol.

• Synchronous protocol.

Asynchronous communications uses start-stop method of communication where characters are sent between nodes, as illustrated in Figure I.1. Special characters are used to control the data flow. Typical ...