OSI MODEL – Layers Explanation

OSI Model stands for Open System Interconnection Model. We will cover all thing about the OSI model in this content.

What is OSI Model?

We know OSI model full form is Open System Interconnection Model. 

Let think, you have a laptop. You using windows as an operating system. Now you want to send data to your friend from your laptop. Both of you have a LAN connection between two laptops. The problem is your friend is using MAC as an operating system. So how you can send the data? Because both of you have using different internal systems.

For this type of problem-solving, OSI was invented by ISO in 1984.

OSI Model Layers Explanation

OSI contains 7 layers. These 7 layers are:

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

Application Layer:

Application layer is used by user end software, like web browser, email, web application, etc. This layer provides a protocol for the software to receive and send data. The common protocol of the application layer is HTTP, HTTPS, FTP, SMTP, DNS, etc.

Presentation Layer:

The presentation layer receives data from the application layer and it’s doing 3 works.  

  1. Translation
  2. Data Compression
  3. Encryption/Decryption

Translation: Presentation layer receives data as characters and numbers from the application layer. Then it converts it as machine-un00000000000.derstandable code like – ASCII. It’s called translation. 

Data Compression: After translation, there are many unnecessary bits. Before transmitting this, the presentation layer also removes the unnecessary bits. This helps to store and transmit it more fastly. It’s called data compression.

Encryption/Decryption: To protect, and keep the data integrity presentation layer also perform the encryption and decryption. Before transmitting, the transmitter encrypts it and, from the receiver end, it’s will decrypt. SSL(Secure Socket Layer) is performing this encrypt and decrypt task.

Session Layer:

The session layer is responsible for authorization and authentication. Authentication or authorization is a process before the connection between server and user. Session layer also helpers of API (Application Programming Interface).

Transport Layer:

Transport layer working for communication through flow control, error control, and segmentation. This layer used TCP(Transport Control Protocol) and UDP(User Datagram Protocol) protocol. UDP is faster than TCP. Because UDP doesn’t provide any feedback during the communication. So UDP can’t restore failed data. Another hand TCP can restore, but slower than UDP. 

Network Layer:

Network layer received data from the transport layer. Here data is sent from one computer to another using data units. Data packets are the units of the network layer.

Also, logical addressing, routing, and path determination is the function of network layer.

Data Link Layer:

Data link layer receives data packets from the network layer. This data pack also contains the address of the sender and receiver. There are two types of addresses are located. 

Logical Addressing
Physical Addressing

The logical address contains the IP address in the data packets. And MAC address is contained by Physical addressing. 

Physical Layer: 

The physical layer is responsible for physical connections like cable, and wireless.  When it’s a cable, the physical layer transmits the electrical signal. When it’s wireless, the physical layer transmits the radio signal. Finally, it’s moving the signal to the application layer, then it’s visible to the user’s computer screen.

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