Computer Network

Q.What is the OSI model ?

The open systems interconnection (OSI) model is a conceptual model created by the International Organization for Standardization which enables diverse communication systems to communicate using standard protocols. In plain English, the OSI provides a standard for different computer systems to be able to communicate with each other.

The OSI Model can be seen as a universal language for computer networking. It is based on the concept of splitting up a communication system into seven abstract layers, each one stacked upon the last.

The seven layers of the OSI model are:

7. Application layer: Data generated by and usable by software applications. The main protocol used at this layer is HTTP.

6. Presentation layer: Data is translated into a form the application can accept. Some authorities consider HTTPS encryption and decryption to take place at this layer.

5. Session layer: Controls connections between computers (this can also be handled at layer 4 by the TCP protocol).

4. Transport layer: Provides the means for transmitting data between the two connected parties, as well as controlling the quality of service. The main protocols used here are TCP and UDP.

3. Network layer: Handles the routing and sending of data between different networks. The most important protocols at this layer are IP and ICMP.

2. Data link layer: Handles communications between devices on the same network. If layer 3 is like the address on a piece of mail, then layer 2 is like indicating the office number or apartment number at that address. Ethernet is the protocol most used here.

1. Physical layer: Packets are converted into electrical, radio, or optical pulses and transmitted as bits (the smallest possible units of information) over wires, radio waves, or cables.

It is important to keep in mind that the OSI model is an abstract conceptualization of the processes that make the Internet work, and interpreting and applying the model to the real-world Internet is sometimes a subjective exercise.

The OSI model is useful for helping people talk about networking equipment and protocols, determining which protocols are used by which software and hardware, and showing roughly how the Internet works. But it is not a rigid step-by-step definition of how Internet connections always function.

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