Learn the OSI Model - [Data Communications, CNT]

Introduction

Data Communications and Computer Networks are two very important subjects in the curriculum of IT and Computer Engineering. The OSI model is very important concept in both of these subjects. The entire subject is layed down on the foundation of the OSI model.

What is  the OSI Model?

The Open Systems Interconnection model (OSI model) was a product of the Open Systems Interconnection effort at the International Organization for Standardization. It is a way of sub-dividing a communications system into smaller parts called layers. Similar communication functions are grouped into logical layers. 

 There are 7 layers in the OSI model :

Description of all Layer 

Application Layer

This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.

Presentation Layer

This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.

Session Layer

This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.

Transport Layer

This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.

Network Layer

This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling,congestion control and packet sequencing.

Data-link Layer

At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers:

·         The Media Access Control (MAC) layer

The MAC sub layer controls how a computer on the network gains access  to the data and permission to  transmit it.

       ·         The Logical Link Control (LLC) layer.

 The LLC layer controls framesynchronization, flow control and error checking.

Physical Layer

This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.

Video Demonstration

 Learn how an message passes through the OSI model using this video:

A complete self-explanatory video on the 7 layers of OSI model and its real-time application. It's an interactive video , so make sure that you click on continue buttons once understand the description at each step.