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OSI Model – Systems Interconnection

The Open System Interconnection-OSI model is very crucial standard for sending and receiving data through a network. It breaks down the entire process into many layers to sent and get data over the computer network system. We shall discuss in the article about the definition of OSI model, how it works, how it plays role to transmit data across its seven layers. Lets us concentrate now about our discussion………


We know that always data travels over networking system from source to destination computers or devices. Many software, hardware, protocols are used to travel data. ISO model has been designed to narrate the whole process of data transmission. We can tell shortly that OSI reference model is a logical layout for network communication that describes how data is sent and received from source to destination medium across the network. This model has been developed by International Organization for  Standardization (ISO) in 1978. Different protocol devices can communicate with each other staying same network through OSI technology. In this model, controls are passed to next layers for further processing.


The OSI model has divided the entire communication process into seven unique layers. The top four layers such as application, presentation, session and transport are defined as hot layers and the other bottom three layers like network, data link and physical are referred to as media layers. Each layer is responsible to perform a particular task until the total communication process is complete between two end-points. The seven layers are-

  1. Application
  2. Presentation
  3. Session
  4. Transport
  5. Network
  6. Data Link
  7. Physical


Now we begin discussion with the lowest layer (physical) and proceeding to the highest layer (application). Let’s focus now…..

Physical Layer: This is the lowest layer of OSI standard. It is responsible for receiving and transmitting unstructured raw bit stream through the physical medium. It works to activate and deactivate physical connections. It encodes data and also converts analog and digital bits into optical or electrical signals. The physical devices used in the layer are Ethernet, cables, token ring, hub, repeaters and connectors. In the physical layer, data are transmitting using electric voltage, radio frequencies, infrared, ordinary lights.

Data Link Layer: The main function of this layer is to synchronize data and also it checks whether data are transferring from one node to another over the physical layer without any errors. It makes a logical link between two nodes and controls frame traffics. In the data link layer, data are encoded and decoded into bits.

Network Layer: In the network layer, source and destination addresses are checked which is defined inside each frame. And then it also see that data has been reached it’s final destination. If data is reached, then this forms data into packets and deliver to transport layer.

Transport Layer: This layer ensures that whether data or messages has delivered with error free, sequence wise and no data losses and without duplication. The transport layer provides message segmentation, acknowledgement, traffic control and session multiplexing. It uses TCP protocol.

Session Layer: This layer controls many communications and also sends data to logical ports. It sets up, coordinates and terminates conversations between two nodes.It uses TCP and UDP protocols to provide service.

Presentation Layer: This layer acts as a translator. This works with operating system. It converts incoming and outgoing data from one format to another. It processes message data such as format conversions, encryption and decryption which will be needed in the application layer. The formats can be ASCII, JPEG, MPEG, MIDI, TIFF.

Application Layer: The top most layer is application layer which is responsible for packaging data received from presentation layer in the data format which is needed by application. That means, it provides network services to end-user applications. The example of applications used in this layer are browsers, SMTP, HTTP and FTP.

This is how; data travels from source to destination node over the network following OSI communication standard.

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