OSI Reference Model

OSI Model

In this blog, we will read about what is OSI model and 7 layers (what is the OSI model and its 7 layers) in very easy language and will read in detail about its benefits, disadvantages, what is a layer. So let's start: -

What is OSI Reference Model
The full name of the OSI model is Open Systems Interconnection. It was developed by ISO (International Organization for Standardization) in 1978 and the model consists of 7 layers.

The OSI model is a reference model for communication between two users in a network. Each layer of this model does not depend on the other layer but data is transmitted from one layer to another.

The OSI model describes how to send and receive data or information in a network. All layers of the OSI model have their own different functions so that data can be easily accessed from one system to another.

The OSI model also describes how network hardware and software function as layers with each other.

OSI Model has 7 Layers

OSI Layers

In the OSI model there are 7 Layers, Now let's know about each of them:

1. Physical Layer

Physical Layer

The physical layer is the lowest layer in the OSI model. This layer is responsible for physical and electrical connections such as - voltage, data rates, etc.

The digital signal in this layer is converted into an electrical signal.

In this layer, the topology of the network i.e. layout of a network (size of the network) is also in this layer.

The physical layer also describes whether the communication will be wireless or wired.

This layer is also called a bit unit.

Its functions:

The physical layer defines how two or more devices connect physically together.

It defines which transmission mode will be between two devices in the network. Which one will be simplex, half-duplex, and full-duplex.

It determines the signal transmitting the information.

2.Datalink Layer

Data-Link Layer

In OSI MODEL the data link layer is the second number layer from the bottom. This layer has two sub-layers: -

* MAC (Media Access Control), and

* LLC (Logic Link Control)

In this layer, packets of data sent by the network layer are decode and encode and this layer also ensures that these packets of data are error-free.

This layer is also called a frame unit. In this layer, two protocols are used for data transmission.

1) high-level data link control (HDLC)

2) PPP (Point-to-Point Protocol)

Its functions:

This layer translates the physical raw bitstream into packets. We call these packets frames. And this layer adds a header and trailer to these frames.

Its main function is to control flow.

In this, a fixed data rate is maintained from both the receiver and the sender. So that no data is corrupted.

It also controls the error. CRC (cyclic redundancy check) is added with a trailer in it so that there is no error in the data.

When two or more devices are connected to a communication channel, then this layer determines which device is given access.

3.Network layer

Network Layer

The network layer is the third layer of the OSI model, in this layer the switching and routing techniques, are used. Its function is logical address ie I.P. Address is also to be provided.

The data in the network layer is in the form of a packet (a group of data) and it is the network layer to transport these packets from source to destination.

This layer is also called a packet unit.

Its functions:

Inter-networking is the main responsibility of the network layer. It provides a logical connection across different devices.

It adds source and destination address to the header of the frame. The address is used to identify devices on the Internet.

The work of this layer is also routing. It determines the best path (s).

4.Transport layer

Transport Layer

The transport layer is the fourth layer of the OSI model. This layer is used to transfer data from the middle of the network correctly. The function of this layer is also to provide communication between two computers.

It is also called a segment unit.

Its functions:

The main function of the transport layer is to transmit data from one computer to another.

When this layer receives the message from the upper layers, it divides the message into very abstract segments. And each segment has a sequence number so that each segment can be easily identified.

It provides two types of service: - connection-oriented and connectionless.

It performs both flow control and error control functions.

5.Session layer

Session Layer

The session layer is the fifth layer of the OSI model that controls connections between many computers.

The session layer provides sessions for communication between two devices, that is, whenever a user opens any website, the session is created between the user's computer system and the website's server.

Simply put, the main function of the session layer is to see how the connections are established, maintained and terminated.

Its function:

The session layer is the same as the dialog controller. This creates a dialog between the two processes.

It also fulfills the task of synchronization. That is, whenever an error occurs in the transmission, the transmission is repeated again.

6.Presentation layer

Presentation Layer

The presentation layer is the sixth layer of the OSI model. This layer is used for encryption and decryption of data. It is also used for data compression. This layer is related to the operating system.

Functions:

The function of this layer is encryption. It is used for privacy.

Its main function is also compression. Compression is very important because we can reduce its size by compressing the data.

7.Application layer

Application Layer

The application layer is the seventh (highest) layer of the OSI model. The main function of the application layer is to interface between our actual application and other layers.

The application layer is closest to the end-user. Protocols like HTTP, FTP, SMTP, and NFS, etc. come under this layer.

This layer controls how an application accesses the network.

functions:

Through the application layer, the user can access the files from the remote computer and retrieve the files.

It also provides the facility to forward and store emails. Through this, we can access the directory from the database.

Advantage of OSI model - benefits of the OSI modelIts benefits are as follows: -

1: - This is a generic model and is considered a standard model.

2: - The OSI model's layers are very specific for services, interfaces, and protocols.

3: - It is a very flexible model because any protocol can be implemented in it.

4: - It supports both connection-oriented and connectionless services.

5: - It uses a divide and conquer technique whereby all services work in different layers. This makes it easy to administrate and maintain the OSI model.

6: - Even if it is changed in one layer, it does not have any effect in the second layer.

7: - It is very secure and adaptable.

Disadvantages of the OSI model

Its disadvantages are as follows: -

1; - It does not define any particular protocol.

2: - It is sometimes difficult to implement new protocols because this model was made before the invention of these protocols.

3: - In this, there is a duplication of services such that both transport and data link layer has an error control method.

4: - All these layers are interdependent on each other.

TCP/IP is the most important after the OSI Model Lets know about it as well

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