An overview Of The OSI Model.
Tags: beginners, tutorial, programming, computerscience
Published: 2022-08-17 07:26:00

In today's article, I am going to discuss the OSI Model as well as its layers. So before going to make any delay Let’s start.

## What is OSI Model?

OSI (Open System Interconnect) is an open standard for all communication systems. International Standard Organization (ISO) introduced the OSI model in 1984. The OSI model has seven layers:

- Physical Layer
- Data Link Layer
- Network Layer
- Transport Layer
- Session Layer
- Presentation Layer
- Application Layer

## OSI Model Diagram


![OSI Model Diagram](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/wc2f9z0a272yki2ddclc.jpg)

Image source: https://commons.wikimedia.org/wiki/File:OSI_model_and_Universal_Identifier_Network_model.jpg

## Physical Layer

It describes the relationship between a device and a transmission medium, such as a copper cable or fiber optic cable. The physical layer is responsible for maintaining voltage and bits. The physical layer works with cable specifications, hubs, repeaters, network adapters, host bus adapters, and more.

The physical layer performs the following functions and services:

- Established and terminates the connection among communication devices.
- Participates in the process whereby the communication resources are effectively shared among multiple users. For example, content resolution and flow control.
- Responsible for sending and receiving data in the form of bits.

Protocol used at the Physical Layer:
- DSL (Digital Subscriber Line)
- ISDN (Integrated Services Digital Network)
- Firewire

## Data Link Layer

Data Link Layer encodes and decodes data packets into bits. It works between the physical layer and the network layer. It is responsible for handling errors in the physical layer, flow control, and synchronization. Data Link Layer divides data into frames and works on frames.

The Data Link Layer is divided into two sun layers:

- Media Access Control (MAC) layer
- Logical Link Control (LLC) layer

**Media Access Control (MAC) layer**

The Media Access Control (MAC) sub-layer controls how a computer on a network gains access to data and permission to send it to another computer or network.

**Logical Link Control (LLC) layer**

Error checking, flow control, and synchronization are responsibilities of the Logical Link Control (LLC) sublayer.

Protocol used at Data Link Layer:
- ARP (Address Resolution Protocol)
- SLIP (Serial Line Internet Protocol)
- PPP (Point to Point Protocol)

## Network Layer

The Network Layer creates logical paths, known as virtual circuits. The Network Layer uses these logical paths for transferring data from one node to another node.

The main tasks of the network layer are as follows:
- Routing
- Forwarding
- Addressing
- Internet working 
- Error handling 
- Congestion control
- Packet sequencing 

Protocol used at Network Layer:
- IP (Internet Protocol)
- ICMP (Internet Control Message Protocol)

## Transport Layer
The Transport Layer is responsible for transferring data between end systems or hosts. It divides data in the form of segments.

Protocol used at Transport Layer:

- TCP (Transmission Control Protocol)
- UDP (User Datagram Protocol)

## Session Layer

The Session Layer is responsible for managing, establishing, and terminating connections between applications (local and remote connections).

The Session Layer provides the following functionality:
- Full-duplex
- Half-duplex
- Simplex operation
- Establishes check ponting
- Adjournment
- Termination 
- Restart procedures

Protocol used at Session Layer:
- NetBIOS (Network Basic Input/Output System)
- SAP (Session Announcement Protocol)

## Presentation Layer

The Presentation Layer is responsible for converting machine-dependent data to machine-independent data. It sends encrypted data on the network. The Presentation Layer is also known as the syntax layer.

Protocol used at Presentation Layer:
- MIME (Multipurpose Internet Mail Extension)
- SSL (Secure Socket Layer)

## Application Layer
The application layer is responsible for providing the interface to the application user.

Protocol used at Application Layer:

- HTTP (HyperText Transfer Protocol)
- FTP (File Transfer Protocol)
- Telnet (Telecommunication Network)
- SMTP (Simple Mail Transfer Protocol)
- IMAP (Internet Mail Transfer Protocol)
- POP (Post Office Protocol)

## Conclusion

We talked today about the OSI (Open System Interconnect) model and also discussed protocols that are used at these layers. I hope you like this article.

I hope you like this article.
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