OSI (Open System Interconnection ) Model in Computer Networks

Introduction

The Open Systems Interconnection (OSI) model is a reference tool for understanding data communications between any two networked systems. It divides the
communications processes into seven layers. Each layer performs specific functions to support the layers above it and offers services to the layers below it.

The three lowest layers focus on passing traffic through the network to an end system. The top four layers come into play in the end system to complete the process.

A networking model offers a generic means to separate computer networking functions into multiple layers. Each of these layers relies on the layers below it to provide supporting capabilities and performs support to the layers above it. Such a model of layered functionality is also called a “protocol stack” or “protocol suite”.

Protocols, or rules, can do their work in either hardware or software or, as with most protocol stacks, in a combination of the two. The nature of these stacks is that the lower layers do their work in hardware or firmware (software that runs on specific hardware chips) while the higher layers work in software.

The main characteristics of the OSI model include the following:

• Helps users understand the big picture of networking

• Helps users understand how hardware and software elements function together

• Makes troubleshooting easier by separating networks into manageable pieces

• Defines terms that networking professionals can use to compare basic functional
relationships on different networks

• Helps users understand new technologies as they are developed

• Aids in interpreting vendor explanations of product functionality

Name of seven OSI model layers are following: -

1. Application Layer

2. Presentation Layer

3. Session Layer

4. Transport Layer