OSI MODEL -


The full name of the OSI model is OPEN SYSTEM INTERCONNECTION . It was developed by ISO in 1978. ISO ie International Standard Organization (INTERNATIONAL STANDARD ORGANISATION).



This model acts as a reference model for communication between 2 users in any network. There are 7 layers in this model i.e. there are seven layers in the OSI model. Each layer has its own separate function. They do not depend on each other, but data transmission takes place from one layer to another. Each layer of the OSI model has its own separate function. So that data can easily reach from one system to another. The OSI model defines how information is received or sent across a network.

The OSI model is just a model, it is not a software, etc., nor is there any protocol that can be installed or run in the system.


7 LAYERS OF OSI MODEL -


First of all friends let me tell you that with the correct model OSI model the layer is divided into 3 classes-

Layer 1,2,3 is called a lower layer or hardware layer.

Layer 4 is called the heart of OSI.

Layer 5,6,7 are called upper layer or software layer.

1 – Physical Layer

2 – Data Link Layer

3 – Network Layer

4 – Transport Layer

5 – Session Layer

6 – Presentation Layer

7 – Application Layer


1. Physical layer


The physical layer is the bottom layer in the OSI model. It is responsible for the physical and electrical connections. In the physical layer, the digital signal is converted into an electric signal. This layer receives signals while receiving data, after which it converts 0 and 1 and then sends them to the data link layer. The physical layer is that the communication will be wired or wireless.

The voltage and data rate required for data transmission is decided in this layer itself. The work of data encoding is also done in this layer. It activates the physical connection, maintains that connection and then also deactivates it.


2. Data link layer


In the data link layer, the data is represented as a frame. The data link layer converts the bit data into frames and gives each frame an address. The data link layer checks that all the data that has come from the physical layer is error free, that is, there is no mistake in it.

The main function of the data link layer is to check that the data that is being sent to the receiver is error free.


3. Network layer


In this layer, data is represented in the form of packets. When the data arrives at the network layer, the source and destination address of the data are checked. So that the data reaches only at its designated place.

To explain in a simple way, the packet which is in the network layer, that is, a group of frames, which is a group of many data, the network layer does the work of transporting those groups to their exact places. The network layer decides which way to send the packet so that it reaches its destination quickly and reaches the exact place.


4. Transport layer


The transport layer is called the heart of the OSI model. The data in this layer is represented in the form of a datagram. The transport layer ensures that the data reaches the receiver in the same order as the sender sent it. And the data should not be repeated again. The transport layer also ensures that how much data can be sent to the sender simultaneously in a time period. The transport layer also checks whether the data that is delivered is complete and error free.


5. Session Layer


The session layer is responsible for opening and closing the communication between 2 devices. The time between the opening and closing of the communication is called the session. The session layer ensures that the session remains open for a long period of time for all the data that is being transferred. And to avoid wasting that data, closes the session immediately.

Let us understand this by giving an example, suppose you are sending data files and if that data stops going in the middle, then session layer sends that data from where the data has stopped and not it will send the data from the beginning.

To explain in simple language, the main function of the session layer is to see how to establish and terminate the connection.


6. Presentation layer


The presentation layer is called the translation layer. Here the data is extracted from the application layer and manipulated according to the required format to be translated over the network. That is, changes are made to the data.

The presentation layer takes care that the data is sent in such a way that the receiver can understand that data and use that data in the right way and at the right time. The language of the two communication systems can be different, under this situation the role of translator plays the role of presentation layer. 


7. Application layer


The application layer is at the top of the OSI model. Which is implemented in the network application. These applications produce the data which is transferred over the network. This network acts as the window for the application service for SS (access). and shows the information received by him. Web browsers such as google chrome, firefox, other applications like skype, office etc are examples of applications.

The application layer supports apps and end users processes. This layer is responsible for file transfer, email and other network services.

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