Open System Interconnection or OSI model was first developed by international organization for standardization in the year 1984. It is only reference model there is no use of it in real life. In real life we use TCP/IP protocols which are based on this model.

OSI model is created to understood the journey of data. Through OSI model you can understand that how data is transferred from one network to another and what processing has been done with this data during transferring. OSI model consist of seven layers these layers are on both side of receiver and sender.

(1) Physical Layer :-

This is the first and lowest layer of OSI model. In this layer data is converted into bits. This is the only layer of OSI model which establish physical communication.

NIC cards and different types of cables comes in physical layer devices. This layer define how many bits transfer in a second. This layer convert bits into signal and then send.

(2) Data Link Layer :-

This in the second layer of OSI model and this is responsible for transport of data in network. There are two sub layers of this layer. This layer organize the pattern of data bits into frames before transmission.

Work of two sub layers of data link layer is given below

Logical Link Control – This sub layer establish link between physical layer and rest of the OSI layers.

MAC – This sub layer control access of physical medium.

(3) Network Layer :-

Network layer is responsible for network communication. In this layer data is converted into packets. This layer provide IP address to data for travelling in network. This IP address sends the data towards its destination. Network layer also transfer the data from one network to another network.

(4) Transport Layer :-

This layer is responsible for reliable transferring of data, data reach the destination in order and error free due to this layer. Transport layer communicate through two ways.

(i) Connection less (UDP) – UDP is used for connection less communication, this type of communication is fast but this is not reliable it does not guaranteed that data reach error free and in order.

(ii) Connection oriented (TCP) – Connection oriented communication take guarantee to reach the destination error free.

(5) Session Layer :-

This layer establish session between sender and receiver and maintain that session till the whole data is transferred. If any session breaks in mid this layer has ability to recover. This layer also terminate the session after data transfer.

(6) Presentation Layer :-

This layer is responsible for presentation of data. This layer verify that amount of data sender is sending is understood by receiver side. Sender and receiver follows same data standards. Some standard are-

txt – ASCII

image – JPG, GIF

audio – MP3, WAV

video – MPEG

these are common data standard on which both side agrees. For example if sender is sending any image then it must be in JPG format so that it is visible to receiver.

If sender and receiver does not agrees same format. Then presentation layer also provide service of conversion and translation.

(7) Application Layer :-

This is the first layer of OSI model. This layer provides interface between user’s application and network. For example – web browsers

Application layer uses some protocols like http, FTP, POP3, SMTP and telnet. These protocols are used to interact with network. Application layer identifies the partner which is communicating and starts the file transferring also.

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