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Working of OSI Model Layer

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There are are a large number of users who use the computer network which is located over the world. In order to ensure the national and worldwide data communication, a robust system has to be developed which is compatible to communication.

ISO, International Organization of Standardization has developed a standard for data transmission. It is OSI model which refers to Open system Interconnection which is a reference model for data transmission over the Internet (Day & Zimmermann, 1983). The OSI model architecture includes seven layers architecture which is mentioned below.

  1. Application Layer
  2. Presentation Layer
  3. Session Layer
  4. Transport Layer
  5. Network Layer
  6. Datalink Layer
  7. Physical Layer

In the below table, we can see different protocols which are working on each Layer of OSI are discussed below:


Name of Protocol

Name of Unit exchanged


Application Protocol

APDU (Application Protocol Data Unit)


Presentation Protocol

PPDU (Presentation Protocol Data Unit)


Session Protocol

SPDU (Session Protocol Data Unit)


Transport Protocol

TPDU (Transport Protocol Data Unit)


Network Layer host-router protocol


Data Link

Data link layer host-router protocol



Physical Layer Host-router Protocol


Features of OSI Model

  1. With the use of sperate network layer, troubleshooting is simple and easy.
  2. Working of software and hardware can be seen efficiently.
  3. Big Picture of communication over the network is understandable in this model.
  4. In this, we can understand new technologies as they are developed.
  5. It is used for comparing the basic functional relationship between different networks.

The Principle of OSI Reference Model

  1. Every Layer will perform a well-defined function.
  2. The layer boundaries should be chosen for minimizing the data flow across the interfaces.
  3. The function of every layer is selected with an eye towards defining internationally standardized protocol.
  4. There are multiple layers which be large enough having different

Functions and components of OSI Layer

Following are some of the functions which is performed in OSI model (Beal, 2018).

  1. Physical Layer
  • Encoding of data is done in this layer.
  • It is the lowest layer of the OSI
  • This layer is responsible for the transmission and reception of unstructured raw data over the entire network architecture.
  • Data rates and voltages are required for transmission of data in this layer.
  1. Data Link Layer
  • In this layer information is synchronize which is transmitted over the physical layer.
  • Transmission of data and receiving data frames sequentially managed in this layer.
  • This layer is responsible for establishing a logical layer between two nodes which manages the Free Traffic control over the entire network. When the Frame buffer is full, it sends signals to transmitting node to stop the transmission of data.
  • This layer is responsible for sending and receiving acknowledgments for frames which are received and sent.
  1. Network Layer
  • The main function of this layer is to decide from which path data should be sent.
  • It routes the signal via different channels from one node to another node.
  • It manages the subnet traffic and acts as a network controller.
  • This layer divides the outgoing data into packets and then assembles the incoming packets into messages for higher levels.
  1. Transport Layer
  • The transport layer is responsible for transmission of data from the parallel path from a single
  • Functions of Multiplexing, splitting and segmentation on data are done by this layer.
  • It receives data from the session layer and then converts the message into smaller units.
  • This layer is very complex depending upon requirements of the network.
  1. Session Layer
  • It manages and synchronizes conversation between two different applications.
  • It transfers data from source to destination session layer streams of data.
  1. Presentation Layer
  • This layer is responsible to take care of the successful data sending to the client.
  • Language (syntax) is different for two communication systems.
  • It performs data compression, data conversion and data encryption etc.
  1. Application Layer
  • It is the topmost layer.
  • The main function of this layer is to hold the application programs.

Merits of OSI Reference Model

  • Protocols in the OSI model are well hidden.
  • It distinguishes between the interfaces, protocols and services.
  • It supports connection-oriented services as well as connectionless services.

De-Merits of OSI Reference Model

  • It is a Reference model only.
  • This model is created before the invention of the protocol.
  • In this model, fitting of the protocol is a tedious
  • This model is not used in the real world.


Beal, V. (2018). The 7 Layers of the OSI Model - Webopedia Study Guide. Retrieved from

Day, J., & Zimmermann, H. (1983). The OSI reference model. Proceedings Of The IEEE71(12), 1334-1340. Retrieved from

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