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 decided in this layer.This is the hardware layer of 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 picture if two machines are connected on the different network. It acts as a network controller to route 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 the destination. Transport layer makes sure that the entire message reaches 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 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.