What is the OSI Model? | 7Layers of OSI Model.

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The Open Systems Interconnection Model (OSI Model) is a conceptual framework that explains the functions of a networking system. It is used to transport data across a network as it goes through different tiers.

What is the OSI Model?

The open systems interconnection (OSI) model is a conceptual paradigm developed by the  International Organization for Standardization that allows disparate communication systems to communicate In layman's terms, the OSI establishes a standard for various computer systems to interact with one another.

The OSI Model may be thought of as a universal computer networking language. It is built on the idea of dividing a communication system into seven abstract levels, each one layered on top of the previous.

Each layer of the OSI Model is responsible for a certain function and communicates with the layers above and below it. DDoS attacks target certain network levels; application layer attacks target layer 7, while protocol layer attacks target layers 3 and 4.

Why is the OSI model important?

Although the contemporary Internet does not fully adhere to the OSI Model (rather, it adheres to the simplified Internet protocol suite), the OSI Model is nevertheless extremely useful for debugging network issues. Whether it’s one person who can’t get their laptop on the Internet, or a web site being down for thousands of users, the OSI Model can help to break down the problem and isolate the source of the trouble.A lot of unneeded work may be avoided if the problem can be focused down to one single layer of the model.

What are the OSI Model's seven layers?

From top to bottom, the OSI model's seven abstraction levels are as follows:

7. Application layer

This is the sole layer that directly interacts with user data. Software applications like web browsers and email clients rely on the application layer to initiate communications. However, it should be noted that client software programmes are not part of the application layer; rather, the application layer is in charge of the protocols and data processing on which the software relies to deliver relevant data to the user. HTTP and SMTP are examples of application layer protocols (Simple Mail Transfer Protocol is one of the protocols that enables email communications).

6. The presentation layer

This layer is largely responsible for preparing data for usage by the application layer; in other words, layer 6 makes data presentable for apps to consume. The presentation layer is responsible for translation, encryption, and compression of data.

Two gadgets that communicate Because several encoding methods may be used while communicating, layer 6 is responsible for transforming incoming data into a syntax that

If the devices are interacting via an encrypted connection, layer 6 is in charge of applying encryption on the sender's end and decoding encryption on the receiver's end so that the application layer may receive unencrypted, readable data.

Finally, the presentation layer is in charge of compressing data received from the application layer before passing it on to layer 5. By reducing the quantity of data exchanged, this improves the speed and efficiency of communication.

5. The session layer

This layer is in charge of starting and shutting communication between the two devices. The session is the period of time between when the communication is initiated and concluded. The session layer guarantees that the session remains open long enough to transfer all of the data being transferred, and then swiftly ends the session to prevent.

Data transport is also synchronised with checkpoints by the session layer. If a 100 megabyte file is being transmitted, for example, the session layer may establish a checkpoint every 5 megabytes. In the case of a disconnect or a crash after 52 megabytes have been transmitted, the session might be continued from the last checkpoint, meaning just 50 more megabytes of data need to be transferred. Without the checkpoints, the entire transfer would have to start over.

4. The transport layer

Layer 4 is in charge of the two devices' end-to-end communication. This comprises transferring data from the session layer and segmenting it before sending it to layer 3. The receiving device's transport layer is in charge of reassembling the segments into data that the session layer can ingest.

The transport layer is also in charge of flow control and fault handling. Flow control establishes an ideal transmission speed to guarantee that a sender with a fast connection does not overwhelm a receiver with a sluggish connection. On the receiving end, the transport layer handles error control by checking that the data received is full and requesting retransmission if it isn't.

3. Network layer

The network layer is responsible for facilitating data transfer between two different networks. If the two communicating devices are on the same network, the network layer is unneeded. On the sender's device, the network layer divides segments from the transport layer into smaller pieces called packets, which are then reassembled on the receiving device. Routing is the process by which the network layer determines the optimum physical path for data to take to reach its destination.

2. The second layer is the data link layer.

The data connection layer is similar to the network layer in that it permits data flow between two devices on the SAME network. The data link layer divides packets from the network layer into smaller pieces known as frames. The data link layer, like the network layer, is in charge of flow control and error control in intra-network communication (The transport layer only does flow control and error control for inter-network communications).

1. The first is the physical layer.

This layer comprises the physical data transport equipment, such as cables and switches. This layer also converts the data into a bit stream, which is a string of 1s and 0s. Both devices' physical layers must also agree on a signal protocol so that the 1s and 0s on both devices may be recognised.

The movement of data across the OSI Model

Human-readable data must go down the seven levels of the OSI Model on the sending device and then up the seven layers on the receiving end in order to be exchanged over a network from one device to another.

For example, Mr. Taylor wishes to send an email to Ms. Parker, Mr. Taylor composes his message in an email application on his laptop and then pushes ‘send’. His email application will send his email message to the application layer, which will select a protocol (SMTP) and forward the data to the presentation layer. The presentation layer will then compress the data before passing it on to the session layer, which will begin the communication session.

The data will then be segmented at the sender's transportation layer before being broken down into packets at the network layer, which will be broken down even further into frames at the data link layer.

When Ms. Parker's computer gets the bit stream over a physical channel (such as her wifi), the data flows through the same set of layers, but in the reverse order. The physical layer will first transform the bitstream from 1s and 0s to frames, which will then be transmitted to the data link layer. The frames will then be reassembled by the data link layer into packets for the network layer. The network layer will next separate the packets into segments for the transport layer, which will reassemble the segments into a single piece of data.

The data will next flow onto the receiver's session layer, which will send it on to the presentation layer before terminating the communication session. The presentation layer will then decompress the data and transfer it up to the application layer. Ms. Parker's email programme will then get the human-readable data from the application layer, allowing her to view Mr. Taylor's email on her laptop screen.