osi model layers and its functions with examples.

OSI MODEL – OPEN SYSTEM INTERCONNECTION

In 1970’s the OSI Model was developed by the ISO - International Organization for Standardization.

OSI - model allowing different networks to work with each other.

This model describes how the data and network information are communicated from one node to another over the different networks.

It fallows 7 Layers to communicating in the TCP/IP Network.

Each and every layer has its unique set of functions, roles or responsibilities.

Application Layer (7th layer):

This layer acts as an interface between the N/w applications and the bottom layers of ISO.

Examples:Email, FTP etc.

Presentation Layer (6th layer):

This layer responsible for presenting the date in the required format.

It performs data translation, code formatting and data compression and decompression.

Example: ASCII conversion

Example: Audio and Video compression.

Session Layer (5th layer):

This layer controls network sessions.

It responsible for how to establishing, managing and terminating the sessions of communicating hosts.

It organizes communication through simplex, half-duplex or full-duplex.

Example: SQL, RPC, NetBIOS.

Transport Layer (4th layer):

It establishes logical connection between the sender and the receiver.

It provides end-to-end communication and it gives a choice of connection oriented or connection less data delivery by the help of TCP and UDP protocols.

Example: It passes segments of data through network layer and reassembles data for the session layers.

Network Layer (3rd layer):

Network layer is responsible for the logical addressing

It determines the best path to reach the destination of all available paths.

Example:

IP addressing is done at this layer.

Routers and firewalls work at this layer.

Data Link Layer (2nd layer):

Data Link layer handles physical transmission of data from one node to another.

This layer ensures that the messages are delivered to the proper device on the LAN using H/w (MAC) addresses.

Example: Switches and Bridges works at this layer.

Physical Layer (1st layer):

It manages physical media, here the data representing as electronic signals from source to destination host.

Example: Repeaters, Hubs, NIC-cards, cat5, coaxial, fiber optic cables work at this layer.