The OSI (Open System Interconnection) Reference Model

OSI was first defined by ISO in 1983 by DAY and ZIMMERMANN and later revised in 1995 by DAY.

Explanation:

OSI Reference Model has seven layers as described below.

1. The Physical Layer

The physical layer takes care of transmission of raw bits over a communication channel. It deals with the basic question like how much voltage should be used to represent a 0 and 1 bit. It make sure that 1 bit should be received as 1 bit and not 0. It decides how communication will be done and how much time it should remain active.

2.   The Data Link Layer

The data link layer breaks the input data into data frames and transmit the frames sequentially. Acknowledge frame is used by receiver to confirm correct receipt of each frame. It deals with the rate of transmission, buffer space to handle multiple speed issues over a network.

3.   The Network Layer

Network layer controls the operation of subnet. Network layer determine how packets are routed from source to destination. Routes can be determined dynamically for each packet based on current network load and status.

4.   The Transport Layer

The transport layer takes make sure data accepted from above layer and split into smaller units ad pass it to network layer. Transport layer determine what type of service to provide to the session layer and ultimately to users of the network. Transport layer is true end-to-end layer, all the way from source to destination.

5.   The Session Layer
 

The session layer allows users on different machine to establish sessions. Session management includes dialog control, token management and synchronization.

  

6.  The Presentation Layer

 

The presentation layer is concerned with the syntax and the semantics of the information transmitted. The presentation layer manages abstract data structures.

7.  The Application Layer
 

The application layer contains a variety of protocols used by users. Common application protocols are used for file transfer, electronic mail etc. One such protocol is HTTP protocol which is basis for World Wide Web.