Introduction to OSI Models and Its Layers in Computer

Open System Interconnection (OSI) is a reference model that specifies how information through one computer’s software system passes through a physical medium to another computer’s software application. The International Organization for Standardization (ISO)introduced the OSI model in 1984, and it today is used as an architectural prototype for inter-computer communications. The OSI model breaks down the process into seven smaller, more achievable steps, with each layer given a certain task. Every layer is self-contained, allowing each layer’s job to be completed individually. 

The Seven Layers of OSI Model

Let’s discuss each layer in detail:

1. Physical Layer

• The physical layer’s primary duty is to transport binary sequences from one node to another.

• It is the OSI model’s lowest layer.

Functions

• It specifies the physical connection between two or more devices.

• It specifies the simplex, half-duplex, or full-duplex mode for the network’s two devices. 

• It determines the arrangement of network devices.

• It regulates the sort of signal that is used to transfer data.

2. Data-Link Layer

• This layer oversees ensuring that data frames are transferred without errors.

• It decides what the data format of the network should be.

• Ensures effective and safe communication among devices.

• It is divided into two layers:

• A layer of Logical Link Control

• A layer of Media Access Control

Functions

• This layer’s job is to turn the binary information provided by the physical layer into packets, called frames.

• This layer adds a header to the frame with a destination address.

• The Data-link layer’s primary role is flow control. It is a technique for maintaining a consistent transmission rate on both sides to prevent data corruption. 

• Error control.

3. Network Layer

It handles device addressing and keeps a record of where devices are on the network. Based on network conditions, service priority, and other considerations, it calculates the optimum path to move data from source to destination. 

Functions:

• The network layer’s primary task is internetworking. It establishes a logical link between many devices.

• Adds the destination address and the source to the header of the frame.

• Routing is a major component of the network layer that identifies the best optimal path from the source to the destination among many paths.

• The sent packets by the higher layer are received here and then again turn them into packets.

4. Transport Layer

The Transport layer is Layer 4, which ensures that messages are sent in the order they are generated, and that data is not copied. This layer’s main responsibility is to complete the transmission of data. It gets data from the higher layer and turns it into segments, which are smaller units.

Two Protocol followed are:

• Transmission Control Protocol

• User Datagram Protocol

Function

Responsible for adding the header, which has the service point address. 

When the transport layer gets a message from the higher layer, it separates it into numerous segments and assigns a sequence number to each segment, which uniquely identifies it.

When the transport layer receives a message from the higher layer, it divides it into many segments and assigns each one a sequence number that uniquely identifies it.

5. Session Layer

The Session layer is responsible for establishing, maintaining, and synchronising communication between devices.

Functions of session layer

• Dialogue control: The session layer works as a dialogue controller, allowing communication between two processes that can be either half-duplex or full-duplex.

• Synchronisation: When transmitting data in a sequence, the session layer inserts certain checkpoints. Synchronisation and recuperation are the terms for this procedure.

6. Presentation Layer

This layer’s main concern is regarding the information that is shared between the two systems. It serves as a data paraphraser of the network. 

Functions of Presentation Layer:

• Translation: It translates data from a sender-dependent format to a common format, which it then converts back to a sender-dependent format at the receiving end.

• Encryption: Encryption is the process of changing information sent by the sender into a different format and sending the resulting message through the network.

• This layer also works in data compaction by reducing the number of bits in order to avail a smooth transfer of data.

7. Application Layer

This layer acts as a window for the users to help them access the network service.

It deals with issues like network transparency, resource allocation, and so on. This layer offers network services to the consumer.

Functions of Application layer

• FTAM stands for File transfer, access, and management in which a user can easily reach files on a remote computer, retrieve files from a computer, as well as manage files on it.

• It is responsible for the email services as well as saving these services.

Conclusion

The OSI model is an important model to learn about as they explain the process of interaction of different computers with one another. I hope this was a good takeaway for all the viewers.