The Open System Interconnection (OSI) reference model is a framework that is divided into seven layers. These seven layers communicate with each other’s. The OSI model describes the conceptual framework for how computers communicate within a network. The OSI model is the first standard model for network communication. It was invented in 1984 by the International Organization for Standardization (ISO). Earlier in 1908, it had been unofficially used by all major telecommunications companies.
The OSI Reference Model is open systems, which have a seven-layer architecture, and all layers have specific functions. All seven layers work to transmit data from one source to another across global.
What is the OSI Reference Model?
The OSI reference model is a reference model, which stands for Open System Interconnection.
- The OSI reference model describes how to move information from a software application on one computer to another software application through a physical medium.
- There are seven layers of OSI models, and each models has performed their own works
- The OSI reference model was developed by the International Organization of Standardization (ISO) in 1984.
- OSI reference model layers have their own tasks, and each layer can be performed independently.
Characteristics of OSI Reference Model
OSI reference layers are divided into two parts, which are called the upper layer and the lower layer.
Upper layer
In the OSI reference model, the upper layer handles the application issue, and it is only for software applications. Upper layers interact with end users and software applications.
Lower layer
In the OSI reference model, the lower layer is responsible for data transport. In the lower layer, the data link layer and transport layer are useful for hardware and software issues. Lower is work on network interface.
7 Layers of OSI Reference Model
In the OSI reference model, there are seven layers. And each layers has their own function. Here I described each layers and its functions.
- Physical Layer
- Data-Link Layer
- Network Layer
- Transport Layer
- Session Layer
- Presentation Layer
- Application Layer
1. Physical Layer
This is the first layer of the OSI reference model. The physical layer transmits the data into bits from one node to another node. physical layer is the lowest layer of the OSI Model. It manages the physical connection, like establish, maintain, and deactivate. The components of physical layer are: Ethernet, ATM, Protocol, RJ45,
Function of Physical Layer
The physical layer defines how to establish the connection between one or more devices. It defines the data transmission like simplex, half-duplex, and full duplex between two nodes. It arrange the topology of the network.
2. Data-Link Layer
This is the second layer of the OSI reference model. It is responsible for error-free transfer of data. It provides efficient communication between two or more devices. It is responsible for unique identification of each devices on a network. Examples: PPD, FDDI, ATM, IEEE, Frame Relay
There are two sub-layers of data-link layer:
Logical Link layer
The logical link layer is responsible for transferring the packet from the receiver end through the network layer. It identified the network layer address for transferring the data. It control the frames synchronizing, flow control and error checking.
Media Access Control Layer
It controls how to access the data and permission to transmit.
Functions of Data Link Layer
It is translate the data in packets, which are called frames. It provides the flow control of data link layer. Flow control, to maintain data speed in a constant rate on both side.
3. Network Layer
The network layer manage the data routing. It manages the packet forwarding of data from IP addresses and mapping the addresses. It manage the addresses of devices and device locations. It provide the path where data moves from source to destination on network. It is responsible for routing and forwarding the data.
Layer 3 devices are the routers that are best example. Routers is provide the specific path to routing on internet. Network layer protocol is used on network layer. Example : IPV4 and IPV6.
Functions of Network Layer
- Networking: It is the main function of the network layer. It provides the logical connection between two devices.
- Addressing: It provides the source and destination addresses of the frame.
- Routing: It provides the best path to the network layer and provides the best path for the routing data from source to destination.
4. Transport Layer
In the OSI layer model, the transport layer manages the data transfer over the network or between hosts. It transfers the data in the session layer and breaks into segments for the transmitted data.
The transport layer manages the flow of the data. Example: TCP, UDP. There are two protocols used in the transport layer:
Transmission Control Protocol (TCP)
This protocol provides the authentication for the system to communicate over the internet. It manages the connection between hosts.
User Datagram Protocol (UDP)
It is also called transport layer protocol. It is an unreliable transport protocol. In this case, when the user received the data, they did not send any acknowledgment that the packet was received.
Functions of Transport Layer
In the transport layer, there are two services provided by the transport layer, that is, connection-oriented and connectionless. In the connectionless services, each segment is treated like individual packets, and these travel from different routes to reach the destination. While connection-oriented services provide the connection for the destination before delivering the packets. All the packets are delivered in a single route for the destination in connection-oriented services. The transport layer manages the data flow from source to destination.
5. Session Layer
The session layer handles the connection between two different devices. It creates the communication channels between devices called sessions. The session layer provides the communication between two devices to open the session, and after the data is transferred, it is responsible to close the session between them. Session layers create a checkpoint during data transfer. Once a session is established, data will be transferred between transport layers.
6. Presentation Layer
The presentation layer works on “syntax processing,” which means that the presentation layer converts the data from one format to another. Example: During a transaction on an e-commerce website, transaction data will exist in the application language. The presentation layer translates this data into network language (101010101), enabling it to transmit and process in the network.
Example: ASCII, EBCDIC, TIFF, GIF, MIDI, JPEG
Function of Presentation Layer
Translation: Presentation layer translate the data into network language (Coding and Encoding)
Data Encryption
For privacy, during the data processing presentation layer, convert the data into encrypted form and transmit the data and result message over the network.
Data Compression
Data is reduced and compressed to a number of bits during transmission. A large amount of data is compressed by the presentation layer.
7. Application Layer
It provides the networking process for the user end. Example: HTTP support for web browsers, emails, and web applications. The network layer follows the transparency of the network and resources.
Function of Application Layer
File Transfer, Access, and Management (FTAM)
The application layer provides access to the file to the end-user and manages the file on a remote computer. Mail Service: It provides the facility of mail forwarding and storage management.
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