Open Systems Interconnection Model(OSI)

OSI (open systems interconnection)MODEL:

For providing communication between two devices international standard organisation(ISO) developed a model known as open systems interconnection(OSI). Osi model isn’t a protocol, it is a model for understanding and designing a specification that’s flexible and robust. It consist of 7 interconnected layers to passes information within the network. Seven layer in osi model are namely.

1.physical

2.data link

3. network

4.transport

5.session

6.presentation

7.application

Physical layer:

Physical layer is responsible for converting frames from datalink layer into bits at the receiving end, and bits from physical layer is given to datalink layer.some of the functions of physical layer is signal coding, representation of bits, physical topology,line configuration, data rate, transmission mode.

Datalink layer:

Datalink layer is responsible for converting packets from network layer into frames at the receiving end, and frames from datalink layer is given to network layer.it makes physical layer error free to the upper layers.some of the fuctions of datalink layer is framing, physical addressing, flow control, error control and access control.

Network layer:

 Network layer is responsible for converting data segements from session layer into packets at the receiving end, and packets from network layer is given to session layer. These layer defines routing for transmitting data from source to destination.some of the funtions of network layer are logical addressing, routing.

Transport layer:

Transport layer is responsible for end-to-end(source to destination) delivery of the entire message the layer converts data into smaller segements for sending and at the receiving end the segements are converted into original data.some of the funtions of transport layer are: service point addressing, segementation and reassembly, connection control, flow control, error control.

Session layer:

Responsibility of session layer is to establish, maintains and disconnects between communicating systems. It provides communication between two devices either in simple or half duplex mode.some of the functions of session layer are dialog control, syncronisation.

Presentation layer:

Presentation layer cares with the syntax and semantics of the knowledge exchanged between two systems. It translates the application into network format and vice versa. some funtions of presentation layer are:Translation, encryption and decryption.

Application layer:

It provides end-users for the processing of data and supports services such as email, file transfer, shared data management, network software services, and other types of distributed information services, this layer acts as an interface between end-users and network. It allows mainly access to network resources.

Fig: OSI model