OSI stands for open system interconnection. It is a conceptual model that characterizes and standardizes the communication functions of a telecommunication/computing system. This model contains seven models, a layer serves the layer above it and is served by a layer below it.

Two instances at the same layer are visualized as connected by a horizontal connection in that layer

1 . Application layer

2 . Presentation layer

3 . Session layer

4 . Transport layer

5 . Network layer

6 . Data link layer

7 . Physical layer

Physical layer

1 . Lowest layer

2 . initiates, maintains and terminates connection

3 . Data rates are defined in this layer

4 . digital/analog bits are converted to electrical or optical signals

5 . data are received and sent at this layer.

6 . data encoding is done in this layer.

Data Link Layer

1 . Manages sequential transmition and receiving of data.

2 . Ensures data transmitted is error free.

3 . It also manages the re-transmition of data

Network Layer 

 

1 . It routes the data to be sent i.e. what route the data should take.

2. It breaks data and reassembled at receiving end for higher 
      layers

Transport Layer

1 . It decides data should take parallel or single path

2 . multiplexing, segmentation take place in this layer.

3 . It converts data into smaller size received from Session layer 

      and passed them to network layer. 

Session Layer

This layer resynchronize data , so that data is not lost prematurely

Presentation Layer

1 . While receiving the data it makes data ready for Application

       layer.

2 . It works as a translator actually.

3 . It decrypts, encrypts, compresses the data

Application Layer

1 . This is the top most layer

2 . It holds program to act upon data.