Describe the purpose and function of each of the seven OSI layers.

Technical Assignment Brief

Subject: Information Technology

Subject Area: Computer Networks

Topic: Understanding the OSI Model and Its Practical Applications in Networking

Brief:

This assignment is designed to help students understand the basic structure and function of the OSI (Open Systems Interconnection) model, which is fundamental to computer networking. Students will explain each of the seven layers of the OSI model and provide simple examples of how data travels through these layers in everyday network communication.

Your task is to:

• Describe the purpose and function of each of the seven OSI layers.
• Provide one practical example for each layer (e.g., HTTP for Application Layer, IP for Network Layer).
• Create a simple diagram showing how data moves through the OSI model.
• Explain why understanding the OSI model is important for IT professionals.

The final submission should be a clear and concise report of approximately 1000 words.

Sample Answer

Introduction

The OSI (Open Systems Interconnection) model is a fundamental concept in computer networking. Developed by the International Organization for Standardization (ISO), the OSI model helps standardise how communication occurs between different computer systems, regardless of their underlying architecture. It breaks down the complex process of networking into seven distinct layers, each with its own purpose and responsibilities. Understanding this model is essential for IT professionals to troubleshoot network problems, design systems, and ensure smooth communication across devices and networks.

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The Seven Layers of the OSI Model

1. Application Layer (Layer 7)

Purpose and Function:
This is the topmost layer of the OSI model. It interacts directly with the end-user and provides services such as email, file transfers, and web browsing. The Application layer doesn’t perform any data processing itself; instead, it supplies network services to user applications.

Practical Example:
HTTP (Hypertext Transfer Protocol) – used by web browsers to request and display websites.

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2. Presentation Layer (Layer 6)

Purpose and Function:
The Presentation layer ensures that the data sent from the application layer of one system is readable by the application layer of another. It is responsible for data translation, encryption, compression, and formatting.

Practical Example:
SSL (Secure Sockets Layer) – used to encrypt data for secure communication over the internet (like HTTPS websites).

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3. Session Layer (Layer 5)

Purpose and Function:
This layer is responsible for establishing, managing, and terminating communication sessions between two computers. It ensures that the session is maintained until all data is successfully exchanged.

Practical Example:
NetBIOS – used in Windows networks to allow applications to communicate over a LAN.

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4. Transport Layer (Layer 4)

Purpose and Function:
The Transport layer ensures that data is delivered error-free, in sequence, and without duplication. It handles flow control and error checking. It can either use connection-oriented transmission (TCP) or connectionless (UDP).

Practical Example:
TCP (Transmission Control Protocol) – used for reliable communication, such as in email (SMTP) and file transfers (FTP).

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