OSI was first defined by ISO in 1983 by DAY and ZIMMERMANN and later revised in
1995 by DAY.
1. The Physical Layer
2. The Data Link Layer
3. The Network Layer
4. The Transport Layer
5. The Session Layer
7. The Application Layer
Explanation:
OSI Reference Model has seven layers as described below.
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.
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.
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.
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.
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.
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.
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