What is OSI (Open System Interconnection) model and how it works


This article is all about what is OSI (Open System Interconnection) model and how it works. In this tutorial, we learn about the internal function of communication. The OSI model (Open System Interconnection model) is a conceptual model that standardizes the communication function of a telecommunication or computing system without regard to their underlying internal structure and technology. Its goal is the interoperability of diverse communication system with standard protocols. This is a theoretical and conceptual model.

In this, we will learn about how a machine and system communicate with another system using different protocols. In other, we can say that in this tutorial we will learn about communication process of systems and electrical machines. The OSI model is consists of seven layers and all the layers are connected with each other. If one of the layers is missing in OSI model then communication does not take place in our systems and machines. So here we will learn about the OSI model and how it works.

Also Read: How to configure DHCP, DNS, HTTP servers along with switches

The different layers of OSI model will be described below in detail.

different layers of OSI model

1.    Physical Layer: –

The physical layer defines the electrical and physical specification of the data connection. In this layer, data is converted into binary language because the computer only knows the binary language. It defines the relationship between a device and a physical transmission medium. This layer allows data to transfer to the next physical layer of the destination host.

2.    Data Link Layer: – 

The data link layer provides point-to-point data transfer through a link between two directly connected nodes. This layer deals with source and destination mac address. It detects and possibly corrects errors that may occur in the physical layer. In other words, it is also known as MAC Access Control Layer. This layer is responsible for controlling how devices in a network gain access to medium and permission to transmit it.

3.    Network Layer: –

This layer deals with source and destinations IP (Internet Protocols) address. A network is a medium through which many hosts are connected, on which every host has an address and which permits hosts connected to it to transfer data to other host connected to it. and the address of the destination host letting the network find the way to deliver the message to the destination host.

4.    Transport Layer: –

The transport layer controls the reliability of a given link through flow control, segmentation/desegmentation, and error control. The transport layer provides the functional and procedural means of transferring variable length data sequences from a source to a destination host via one or more networks with maintaining the quality of service functions. The transport layer also provides the acknowledgment of the successful data transmission and sends the next data if no errors occur.

This includes two protocols: –

1.   TCP (Transmission control protocol): – TCP/IP protocol is slower than UDP but it is more secure and reliable than UDP protocol and it also provides the facility of acknowledgment.

2.   UDP (User datagram protocol): – UDP is faster than TCP but it is not reliable and does not provide the facility of acknowledgment.

5.    Session layer: –

This session layer controls the connection between computers. This layer controls the modes and ways of transmitting data between two computers and hosts.

It is generally of three types they are described below: –

1.  Simplex: – In this type of operation only one direction transmission will take place. In the simplex, transmission sender can send only and receiver can receive only. So this type of transmission is not reliable to us but this type of transmission will be also used at some places like television transmission.

2.  Half-Duplex: – In this type of operation transmission takes place in both the direction but not at a time (simultaneously). In other words, we can say that both sender and receiver cannot send data at the same time. This type of operation will be used in secret conversions like Walkie-Talkie.

3.  Full-Duplex: – In this type of operation transmission takes place in both the directions simultaneously (at the same time). In this type of transmission sender and receiver can send data at the same time. This type of transmission mainly used in cell phone, mobile phone, computers etc.

6.    Presentation layer: – 

In the presentation layer provides the platform on which encryption, decryption, and compression, decompression takes place. In this layer, our main message will be converted into an encrypted form to enhance the security of your message and at the receivers end, it will be allowed the receiver to decrypt that message.

7.    Application layer: –

The Application layer is the main layer of the OSI model in this layer all the applications and Softwares exists that supports HTML, HTTP, FTP and SMTP protocols. This layer generally contains web browsers and web applications by which we can communicate easily with another host through the internet.

To understand these OSI model perfectly we take an example. In this example, we describe that how a mail is transmitted from one host to another host through the internet. Let’s start here 

working of OSI model

Description of these steps in detail will be given below.

         HOST A              HOST B
1. In Application layer, a user creates a mail in the web browser on their system. ⇓ 7.  In Application layer, receiver read senders mail in the browser on their system.
2. In the Presentation layer, our created mail will be converted into encrypted form and compressed its size also. ⇓ 6.  In the Presentation layer, receivers system decrypt data and send it to the last layer that is application layer. ⇑
3. In the Sessional layer, it will check for senders systems specification and choose either simplex, half-duplex or full-duplex. ⇓ 5.  In the Sessional layer, packet check whether your system supports either simplex, half-duplex or full-duplex. ⇑
4. In the Transportation layer, it will check for senders mode of transportation that is either TCP or UDP. ⇓ 4.  In the Transportation layer, packet check whether your system supports TCP and UDP protocol or not. ⇑
5. In the Network layer, it will collect senders (source) and receivers (destination) IP address with the packet. ⇓ 3.  In the Network layer, packet check receivers IP address. If IP address is matched then it will pass data to next layer. ⇑
6. In the Data link layer, it will collect senders (source) and receivers (destination) MAC address to enhance the security of your package. ⇓ 2.  In the Data link layer, packet checks the MAC address of the receiver. If Mac address is matched then it will pass data to next layer. ⇑
7. In the Physical layer, our package converts into the binary language from the normal language. Because our system only supports binary language. ⇓ 1.  This is the first layer for receivers system that is the Physical layer. In this layer, data will be received by the receiver in binary form. In other words, data reaches its destination. ⇑
 After that our mail is transferred through the wires and wireless medium and reaches the physical layer of another user.


This is the process by which we easily understand the working of an OSI model in depth. If you have any queries regarding this solved out through the comment section and also provide feedback to us because your feedback is valuable to us.

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