The open system interconnection (OSI) is the layer model for the network system designed by ISO(International organization for standardization).OSI enables devices in the network to communicate with each other .
There are seven layers related to each other for their functionality.Each layer calls for the service of the layer below it.
At the physical layer ,the communication is direct.the communication flows from the highest layer of the sending computer to its lowest layer.this communication then flows to the lowest layer of the receiving computer till it reaches to the highest layer.
The layer at the sending computer add some information to the original message received from a layer above it.This information is in the form of header & trailers.The header & trailer information represents the control data appended at the beginning and end respectively. The control data enables the message to be transmitted at the appropriate destination.
Headers are added to the information at the data link layer, network layer,transport layer , session layer and presentation layer, whereas trailer is generally added at data link layer only.The sender node adds these headers & trailers the receiving node checks & interprets the headers & trailer.
At layer 1 of the sending computer the message is converted in a form,which can be transferred to the layer receiving computer.This message is converted back to the original form through each layer on the receiving machine.
The Seven Layer of OSI Model is :-
Application Layer
Presentation Layer
Session Layer
Transport Layer
Network Layer
Data Link Layer
Physical Layer
