7 layers of OSI Reference Model | Functions of OSI Layer in Computer Network

Do you want to know the functions of 7 layers of OSI reference model in a computer network? So in this post, the 7 layers of OSI reference model has been explained in detail. After reading this article, you can get complete information about the OSI model.

When the development of computer networks started increasing, then creating and managing the network also became very complicated. At that time, new companies were creating their own operating systems and were also making new network devices, connecting all of them to the network and communicating with each other had become a very difficult task.

In 1978, ISO (international organization for standardization) introduced a network architect to connect different devices into a network by looking at this problem. Finally, in 1984, ISO created a reference model of the same network architecture and made it public under the name of the 7 layers in computer network of OSI reference model (Open System Interconnection).

What is the OSI layers in computer network?

The full form of the OSI model is Open System Interconnection Model. This model connects networks all over the world with each other and makes communication between them. According to the data transmission, this OSI model is divided into 7 layers in computer network.

7 layers of OSI reference model

This model is not some kind of software or protocol, here is a reference model. In which data is transferred from one system to another. Each layer has a different function. In this model all the layers are not dependent on each other, so the data transfer is done properly.

7 layers of OSI reference model

The OSI model is composed of seven ordered layers.

  • Application Layer
  • Presentation Layer
  • Session Layer
  • Transport Layer
  • Network Layer
  • Data link Layer
  • Physical Layer

This OSI model is divided into 7 layers and 3 sub-groups. The first 3 layers are the physical layer, data link layer, and network layer for network support. They deal with the physical aspects of moving data from one device to another

The transport layer belongs to the second subgroup. This ensures that the data transmitted by the lower 3 layers is in a form that the upper layers can access.

Layers 5, 6, and 7 which are the session layer, application layer, and presentation layer are all used for user support. Let’s know about the 7 layers of OSI reference model.

Physical layer

It converts the incoming data from the upper layers into 1s and 0s for transmission over the media. then physically transfers data from one computer to another. It is actually responsible for the physical connection.

A physical connection can be made using such twisted pair cable, fiber-optic, coaxial cable, or wireless communication media. This layer receives the frames sent by the data link layer and soon converts them into signals that are compatible with other transmission media.

Functions of the physical layer

  • It transmits the bits to electrical or optical signals which are appropriate for the physical medium.
  • The physical layer manages the way devices are connected to network media.
  • The physical layer defines the transmission rate. Which means how many bits are sent in a second. This is called the duration of the bit.
  • It defines the manner in which the equipment will be connected through the medium.
  • The physical layer also defines the direction of transmission between two devices.

For Example simplex, half-duplex, or full-duplex.

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Data link layer

The data link layer is the 2 layer of the OSI reference model in computer network. This layer is responsible for the delivery of data from one node to another. Here the network fills the data received from the layer into a frame and after that this layer sends that frame to the physical layer.

The data link layer provides error-free transfer of data frames from one node to another and allows the above layers to error-free transmission over the link. It defines the format of the data in the network.

A network packet contains the checksum, source and destination address, and data in a single frame. The data link layer handles the physical and logical connections to the destination of the packet using the network interface. This layer consists of 2 sub-layer.

  • Logical link layer- Here it provides addressing information for communication to the data pocket in the entire network.
  • Media access control: Here it is helpful to make communication links between two physical devices.

Functions of Data link layer

  • The data link layer combines the physical raw bits to form a packet called a frame.
  • In this layer, a header is used in front of the frame to identify the destination. Therefore, the header is added to the frame, and it is sent to its destination address.
  • This layer prevents data flow control and error control.
  • The layer has a feature that if a frame is damaged or lost, then it detects that data and retransmits them.
  • When two or more devices are connected to the same link, the data Link-layer protocols determine which device has control over the link at a given point in time.

Network layer

In all networks, the network layer is responsible for carrying the data packets from the source to the destination. So, the network layer ensures that each packet reaches its final destination properly from its origin.

If two systems are connected to different networks with devices such as routers, the network layer is used. If two systems are connected by the same link, there is no need for a network layer.

The network layer also provides routing and switching technology. In addition, error handling, packet sequencing, internetworking, addressing, and congestion control are all core functions. The function of this layer is to provide an IP address.

Functions of Network layer

  • The main function of the network layer is to determine the right path from the source to the destination at the time of sending data packets.
  • A header is used in network layer packets, which contain the source and destination address of that packet.
  • This layer receives the data packet from the upper layer i.e. the transport layer and after converting that packet according to it and sends it to the next layer. This process is called packetizing.

Transport layer

The transport layer provides end-to-end message delivery across a network as well as error checking. The main function of the transport layer is to transfer the data from one computer to another computer without any error and in a proper sequence.

The size and complexity of the Transport Protocol depend on the type of service it is receiving from the network layer. This layer provides communication between two computers. It communicates in two ways, Connectionless and Connection-Oriented.

Connectionless:

In this type of transmission, the receiver does not send any acknowledgement of receiving the data to the source. it allows much faster communication between devices. Its demerit is that connectionless transmission is less reliable compared to connection-oriented.

Connection-Oriented

In this type of transmission, the receiver after receiving the data sends an acknowledgement of the data being received to the sender. This is a slow transmission method. Connection-oriented transmission is a reliable transmission method because it requires more data packets to send across the network.

If there is some problem with the data being sent from the source then the receiver requests the sender to resend that data and sends an acknowledgement of that data that is correct.

Functions of transport layer

The main function of the transport layer is to transmit the data in a process. The responsibility of the network layer is to send the data from one computer to another.

When the transport layer receives data from the upper layer, it divides that data into several segments. When it is time to send that data, the layer sends it to another layer based on the sequence.

The transport layer is responsible for flow control and error control. Error control is performed end-to-end rather than single-link. The transport layer ensures that all the messages reach their destination without any errors.

Session Layer

Basically, the primary responsibility of the session layer is to initiate, maintain and end communication between two devices. which are called sessions. It also provides orderly communication to regulate the flow of data between devices.          

The session layer ensures that whatever data is being transferred, the session remains open until the data transfer details and that the session is closed when the data transfer is over.

Functions of Session layer

The session layer allows two systems to enter into a dialogue. This allows communication between two processes to occur in either half-duplex (one way at a time) or full-duplex (two ways at a time) mode.

In case of data transfer in a sequence, the session layer adds some checkpoints to that path because if some error occurs at the time of data transmission, it re-transmits that data through that checkpoint. This process is known as synchronization and recovery.

Presentation Layer

The presentation layer is called the 6th layer. This layer is also called the translation layer. Because the Presentation Layer presents different formats of data between two different types of systems by converting them into a uniform format. It deals with the syntax and semantics of the information exchanged between two devices.

Functions of Presentation Layer

  • The 3 main functions of this layer are Translation, Compression, and Encryption.
  • It is used for data privacy and security.

Application Layer

It is the seventh layer of the OSI Model. This layer is user-friendly, which allows it to communicate between the computer application and other layers of the OSI model. Due to this layer being close to the end-user, it has many protocols in it.

For example:

HTTP– HyperText Transfer Protocol (used on the internet).

DNS– Domain Name System (It is used to resolve the domain name into an IP address).

Telnet– Terminal Emulation Program (It is used to access and utilize the memory and processing power of the host).

Boot P– Boot stamp protocol (Used for client-server application).

FTP– File Transfer Protocol (Uploading and downloading files from the internet).

SMTP– Simple Mail Transfer Protocol (used to send mail from system to ISP).

POP3– Post Office Protocol 3 (Accessing mail).

Functions of Application Layer

  • The application layer allows a user to access, retrieve and upload files from a remote computer.
  • This layer gives the facility to various e-mail services and store data.
  • It provides Inter-process communication, Network management, Directory services, and Electronic messaging services.

Conclusion

The 7 layers of OSI reference model in the computer network are considered a conceptual model that helps in transmitting data from one network to another network. Apart from this, data transmission can be done in a good way, so it has been divided into 7 layers in computer network.

In this article, We have provided complete information about the functions of 7 layers of OSI Reference Model in Computer Network. I hope you all must have understood this article. If you feel any kind of deficiency in this article or have any kind of doubt, then you can write in the comment box.

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