OSI model

The OSI model is a layered approach to networking. OSI stands for Open Systems Interconnection. It was developed by ISO – ‘International Organization of Standardization‘, in the year 1974.
 An abstract model of networking, called the Basic Reference Model or seven-layer model it is a 7 layer architecture with each layer having specific functionality to performed. All 7 layers work together to transmit the data.
This image was taken from geeksforgeeks.org
I am describing them to you in descending order because, I personally believe that this model can be easily understood in this order.
( Please note: OSI model is not implemented in Internet because of its late invention. Current model being used is the TCP/IP model. TCP/IP model k baraime phir kabhi batt karege abhi merko alas aa raha hai )

7. Application Layer (Layer 7) :

At the very top of the OSI Reference Model stack of layers, we find Application layer which is implemented by the network applications. Application Layer is also called as Desktop Layer. The application layer is the OSI layer closest to the end user, which means both the OSI application layer and the user interact directly with the software application. This layer interacts with software applications that implement a communicating component. This layer is responsible for communicating directly with the application itself.

6. Presentation Layer (Layer 6) :

This Layer is responsible for anything involved with formatting of a packet like compression, encryption, decoding, and character mapping. if you receive message and text is gobbledygook ( agar meaning nahi pata tho iss par ek barr click kardo bhai), you have a problem related to presentation layer.Presentation layer is also called the Translation layer and  Syntax layer.The data from the application layer is extracted here and manipulated as per the required format to transmit to Session layer. And then again Receive data from Session layer and manipulate as per the required format to transmit over the application layer. I would take it as broker or translator in between Application layer and Session layer.

5. Session Layer (Layer 5) :

This layer is responsible for establishing connection or session  and also ensures security between two endpoints (usually application) It makes sure that both application on other hand has the correct parameters set up to establish bidirectional communication with source application.

4. Transport Layer (Layer 4) :  

This layer provides communication between one application program and another. Depending on the protocol, it may be responsible for error detection and recovery, transport-layer session establishment and termination, multiplexing, fragmentation, and flow control.

3. Network layer (layer 3) :

This layer is primarily responsible for logical addressing and path determination, or routing, between logical address groupings.

2. Datalink layer (layer 2) :

This layer is responsible for physical addressing and network interface card (NIC) control. Depending on the protocol, this layer may perform flow control as well.
This layer also adds the FCS, giving it some ability to detect errors.


1. Physical layer (layer 1) :

The simplest of all layers, this layer merely deals with physical characteristics of a network connection: cabling, connectors, and anything else purely physical. This layer is also responsible for the conversion of bits and bytes
(1's and O's) to a physical representation (electrical impulses, waves, or optical signals) and back to bits on the receiving side.

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