What is OSI Model? Easiest method to understand OSI Layers.

In this article, you will understand the OSI model in the simple and easiest way. In this article, we learn why we need the OSI model? And What is the OSI reference model? What are the Functions of OSI layers? Types of its layers. Let’s discuss its definition, types of Osi model and functions of OSI models layers.

All around the world, there are numbers of users who use the computer network. So to communicate all the user of worldwide, a system is developed which is capable to communicate and share huge data all over the world with a specified standard.

OSI stands for Open System Interconnection is a reference model that describes how information from a software application in one computer moves through a physical medium to the software application in another computer.The Open Systems Interconnection model (OSI model) is a concept based model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology. This is called a model for Open System Interconnection (OSI) and world widely known as OSI model.


OSI consists of seven layers, and each layer performs a particular network function… The seven layers are:

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

Following is the brief information about the OSI model specified the protocols used and the data unit exchanged by each layer.

Image of OSI MODEL
Data unit and Functions of the OSI Model

Feature of the OSI Model

  1. Communication over networks is understandable through this OSI model.
  2. We can observe how hardware and software work together.
  3. We can understand the working technologies.
  4. We can troubleshoot it in a very easier way because of separate networks.
  5. Basic functionality on different networks can be compared with the OSI Model.

Functions of Different Layers

Following are the functions performed by each layer of the OSI model. This is just an introduction, we will cover each layer in details in the coming tutorials.

OSI Model Layer 1: The Physical Layer

  1. Physical Layer is the lowest layer of the OSI Model.
  2. Physical layer technologies are ones that are at the very lowest level and deal with the actual ones and zeroes that are sent over the network.
  3. The physical layer is also considered the domain of many hardware-related network design issues, such as LAN and WAN topology.
  4. Physical Layer is also for Data encoding.

OSI Model Layer 2: Data Link Layer

  1. This layer of synchronizes the information over the physical layer.
  2. The data link layer is the lowest layer in the OSI model that is concerned with addressing: labelling information with a particular destination location.
  3. This layer sends and expects acknowledgements for frames received and sent respectively.
  4. Data Link Layer establishes a logical layer between two nodes and also manages the Frame traffic control over the network. It signals the transmitting node to stop when the frame buffers are full.

OSI Model Layer 3: The Network Layer

  1. Network Layer routes the signal through different channels from one node to other.
  2.  The network layer controls the operation of the subnet.
  3. It divides the outgoing messages into packets and assembles the incoming packets into messages for higher levels.
OSI MOdel Image
OSI MOdel Image

OSI Model Layer 4: Transport Layer

  1. It decides whether data transmission should be on a parallel path or single path.
  2. This Layer does functions such as Multiplexing, Segmenting or Splitting into the data.
  3. It collects data from the Session layer, converts this data into smaller units and dispatches it on to the Network layer.
  4. The complexity of Transport Layer depends upon the network requirements.
  5. Transport layer breaks the message (data) into small units so that they are handled more efficiently by the network layer.

OSI Model Layer 5: The Session Layer

  1. Session Layer manages and synchronize the conversation between two different applications.
  2. The session layer provides the mechanism for opening, closing and managing a session between end-user application processes, i.e. a semi-permanent dialogue.
  3.  It prevents the two users to simultaneously attempt the same critical operation.

OSI Model Layer 6: The Presentation Layer

  1.  The Presentation layer ensures the information that the application layer of one system sends out is readable by the application layer of another system.
  2. While receiving the data, the presentation layer transforms the data to be ready for the application layer.
  3. The presentation layer is the lowest layer at which application programmers consider data structure and presentation, instead of simply sending data in the form of datagrams or packets between hosts.
  4. It performs Data compression, Data encryption, Data conversion etc.

OSI Model Layer 7: Application Layer

  1. It is the topmost layer.
  2. The Application layer identifies the availability of communication partners for an application with data to transmit.
  3. The application layer programs are based on client and servers.
  4. Services like Mailing, directory services, resourcing network etc. are provided by the application layer.
  5. Main work of this layer is to catch application programs to act upon the received data and to be data sent.

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