OSI Model (Open System Interconnection Model) was developed in 1983 by the representatives of major telecommunication and computer companies. OSI architecture was officially adopted as an International standard by the International Standardization Organisation (ISO). The main concept of OSI is that the process of communication between two endpoints in a network can be divided into seven distinct groups of related functions or layers. Each communicating user or program is on a device that can provide those seven layers of function.

In this architecture, each layer serves the layer above it and it is served by the layer below it, i.e. layer 2 will serve the layer 3 and layer 2 is served by layer 1. So, in a given message between users, there will be a flow of data down through the layers in the source computer, across the network, and then finally moves to the destination computer.

The seven layers of the OSI model are described as:

Application layer

In this layer, the capacity of the communication network is identified and the communication partners are identified. Is there someone to talk? Will the network allows connecting right now? These types of decisions are part of application layer functioning.

Presentation layer

This layer is usually part of an operating system and converts incoming and outgoing data from one presentation format to another, e.g. from clear text to encrypted text at one end and back to clear text at the other end.

Session layer

This layer sets up, coordinates and terminates conversations. Its services include authentication and reconnection after an interruption. On the internet, Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) provide these services for most applications.

Transport layer

This layer manages the task to convert data into packets and checks error if any in the data when it is received.

Network layer

This layer handles addressing and routing the data — sending it in the right direction to the right destination and receiving incoming transmissions at the packet level. IP is the network layer for the internet. IPv6 is the latest version of Internet Protocol.

Data link layer

This layer sets up links across the physical network and puts packets into network frames.

Physical layer

This layer conveys the stream of bits across the network either electrically, mechanically or through radio waves. The physical layer covers a variety of devices and mediums, e.g. optical fibres, coaxial cables, connectors, receivers, transceivers and repeaters etc.

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