What is OSI Model and its Layers

What is OSI Model?

An OSI model is an “Open System Interconnection”, It is developed by the International Organization for Standardization (ISO) in 1984. It is a reference model that deals with connecting the system via the network.

Basically, the OSI model tells how applications can able to communicate with each other via the network. It is used for transferring the data to other systems via the network which moves through different layers. In an OSI model, there are seven layers are there let see:

Layers of OSI Model

  1. Physical Layer
  2. Data Link Layer
  3. Network Layer
  4. Transport Layer
  5. Session Layer
  6. Presentation Layer
  7. Application Layer 
OSI Model

Now let’s see all these layers one by one:

1) Physical Layer

As you can see in the given diagram of the OSI model the physical layer are at the bottom, this is because the physical layer is responsible for physical connectivity between the physical devices via the network. It helps to transfer the data from one node to another node to the physical devices like cables, modems, adapters, etc. It is known as the “Physical Layer”

2) Data Link Layer

It is the second lowest layer of the OSI model, The main task of this layer is to provide error-free transmission from one node to another. It takes data packets from the networks and converts them into smaller pieces which are known as “Frames”. When a data packet arrives over the network then the Data Link Layer is responsible for transmitting those packets to the Host using its MAC address. It is a “Data Link Layer”.

The data link layer has two sub-layers are:

  1. Media Acess Control (MAC)
  2. Logical Link Control (LLC)

3) Network layer

The network layer ensures that each packet of data travels successfully and efficiently from its sources to its destination across various networks. In this layer, “routers” are used to transfer packets for transmission. It uses the IP address to find out the destination address where to send it. This is known as the “Network Layer”.

4) Transport Layer

The transport layer is the heart of the OSI model, this is because it has an important responsibility of end-to-end communication between the devices. This layer ensures that the transmission of data is done successfully or not, if there is some error when transferring the data then it is responsible for retransferring those data. It is known as the “Transport Layer”

5) Session Layer

The main task of this layer is to provide the session establishment, session release, synchronization, data exchange, expedited data exchange, etc. It allows users on different machines to establish the session between them. It is known as “Session Layer”

In simple words, we can say that when a computer wants to communicate with other devices then the session is needed to be created that’s why this layer helps to provide the session for communicating with the devices.

6) Presentation Layer

Unlike all the lower layers, which are just interested in moving bit reliably from here to there, the presentation layer is concerned with the syntax and semantics of the information transmitted. It is a “Presentation Layer”

In simple word, the presentation layer takes the data from the application layer and translates them into EBCDIC code (extended binary code decimal interchange code), and transfers it to the networks. By default, the data of the application layer is in ASCII code (American standard code for information interchange) then in the presentation layer it translates it into EBCDIC Code.

7) Application Layer

Well, this layer is the top layer of the OSI model, this layer(application layer) is also known as the “Desktop Layer” because it allows users to interact with applications so that user can read and writes messages, transfers files, and much more. Applications like: Chrome, Skype, Outlook, etc.

The application layer produces the data which has to be transferred over the network. This layer also serves as a window so that the users can use their favorite applications. This is known as the“Application Layer”

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