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OSI Model



The OSI Model (Open System Interconnection) is a framework to define the protocol implementation in computer networking.

OSI Layers:
OSI model constitutes of 7 layers defined below.

Physical Layer :
The form of data at this layer is a bit stream which has to be encoded into signal for further transmission it also decides what encoding type would be applicable on transmission.Transmission rate is also decide in this layer.This is the Hardware layer of the OSI .Devices like repeater, hub, cables, ethernet involved in this layer.
Data Link Layer :
This layer is responsible for encoding and decoding of the electrical signals into bits.It manages data errors from the physical layer and converts electrical signals into frames.
Network Layer :
 This layer is responsible to deliver packets from source to destination across multiple networks. It comes into the picture If two machines are connected on the different network. It acts as a network controller  to routes the signals.It is also responsible to convert the outgoing messages into packets and to convert incoming packets into messages.Routers and gateways operate in this layer. 
Transport Layer :
This layer is responsible to deliver the entire message to destination. Transport layer makes sure that the entire  message reach destination in order. It also decides data transmission mode ( parallel path or single path).Transport layer breaks the packets into small units.
Session Layer :
This layer is responsible for managing connections and sessions between applications.
Presentation Layer:
This layer is responsible for the syntax and semantics of the message exchanged. This layers plays a role of translator in case of both the communications system's syntax are different so that they can understand each other's language.
Application Layer:
This layer is responsible for application services for file transfers, e-mail, and other network software services.
Protocols like FTP, HTTP work on this layer.

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