What is OSI Model

The OSI Model is a logical and conceptual model that describes network communication that is used by systems that are open to interconnection and other systems. The Open System Interconnection (OSI Model) also describes a logical network and uses different layers of protocols to efficiently explain computer packet transfer.

Characteristics of OSI Model

  • A layer can only be generated where the abstraction levels are definite.
  • Each layer’s role should be chosen according to the protocols that are internationally standardized.
  • The number of layers should be high so that there is no need to insert different functions into the same layer. It should be small enough at the same time, so that design doesn't get too complicated.
  • In the OSI model, for performing basic functions each layer relies on the next lower layer. Each level should be able to provide the next higher layer of services
  • Changes in one layer do not necessitate adjustments in other layers.

7 Layers of the OSI Model

OSI model is a layered server architecture system in which each layer is defined according to a specific function to perform. All these seven layers work collaboratively to transmit the data from one layer to anoth

  • The Upper Layers: It deals with application issues and mostly implemented only in software. The highest is closest to the end system user. In this layer, communication from one end-user to another begins by using the interaction between the application layer. It will process all the way to end-user.
  • The Lower Layers: These layers handle activities related to data transport. The physical layer and data link layers also implemented in software and hardware.

Upper and Lower layers further divide network architecture into seven different layers as below.

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

Differences between OSI & TCP/IP

OSI Model

  1. OSI model provides a clear distinction between interfaces, services, and protocols.
  2. OSI uses the network layer to define routing standards and protocols.
  3. OSI model use two separate layers physical and data link to define the functionality of the bottom layers.
  4. OSI model, the transport layer is only connection-oriented.
  5. In OSI model, data link layer and physical are separate layers.
  6. The minimum size of the OSI header is 5 bytes.

TCP/IP Model

  1. TCP/IP doesn't offer any clear distinguishing points between services, interfaces, and protocols.
  2. TCP/IP uses only the Internet layer.
  3. TCP/IP uses only one layer (link).
  4. A layer of the TCP/IP model is both connection-oriented and connectionless.
  5. In TCP data link layer and physical layer are combined as a single host-to-network layer.
  6. Minimum header size is 20 bytes.

Advantages of the OSI Model

  • It helps you to standardize router, switch, motherboard, and other hardware.
  • Reduces complexity and standardizes interfaces.
  • Facilitates Modular Engineering.
  • Helps you to ensure interoperable technology.
  • Helps you to accelerate the evolution.
  • Protocols can be replaced by new protocols when technology changes.
  • Provide support for connection-oriented services as well as connectionless service.
  • It is a standard model in computer networking.
  • Supports connectionless and connection-oriented services.
  • Offers flexibility to adapt to various types of protocols.

Disadvantages of the OSI Model

  • Fitting of protocols is a tedious task.
  • You can only use it as a reference model.
  • In the OSI network layer model, some services are duplicated in many layers such as the transport and data link layers
  • Layers can't work in parallel as each layer need to wait to obtain data from the previous layer.