The Open System Interconnection (OSI) Reference Model was created as the first step towards the standardization of protocols by the International Standards Organization (ISO) in 1984. It is also called as the OSI Seven Layer Model as it divides the network architecture into seven distinct layers.
- The OSI model has layered architecture wherein each layer offers certain services to the layer below it and there is abstraction present between layers.
- Each layer passes data and information to the layer below it till the lowest layer where actual communication takes place.
- The function of each layer varies which helps in reducing the complexity.
- Protocols, services and interfaces form the basis of the model. Where protocols are the rules that layers have to follow while exchanging information, services are the set of actions provided by the layers and interfaces are the medium that layers use to communicate with other layers.
Advantages of OSI Model :
- OSI model supports layered architecture and modular engineering.
- Both connection-oriented and connectionless services are supported by OSI model.
- It implements abstraction between the layers such that, the changes made by the above layer does not affect the layer below it.
- It provides flexibility to adapt to new protocols with technological advancements.
- It reduces complexity as the services are divided into the 7 layers.
Disadvantages of OSI Model :
- OSI is a reference model. Thus, its practical application is restricted.
- Duplication of some services in layers is observed such as both the transport layer and data link layer have error control mechanism.
- The layers cannot work in parallel as each layer has to wait in order to receive data from the layer above it.
- The protocols in some of the layers were never fully defined such as the presentation and session layer.
- When OSI model was introduced, TCP/IP was already in place and thus changing it would require a lot of time and money and mainly because a lot of time and money had been spent on developing TCP/IP.
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