Advantages of OSI Model | disadvantages of OSI Model

This page covers advantages and disadvantages of OSI Model. It mentions OSI Model advantages or benefits and OSI Model disadvantages or drawbacks. OSI stands for Open System Interconnection.

What is OSI Model?

Introduction:
• OSI model was intended to be a blueprint for a set of worldwide communication standards. This enables computers across the world to be interconnected easily.
• OSI model has 7 layers viz. physical, datalink, network, transport, session, presentation and application.
• The purpose of classification of layers in OSI model is to define specific protocol, function, independent design and testing of components for a particular class of a problem.

Physical:
It mainly takes care of bit stream transmission over physical medium (cable, air etc.). It provides the hardware means of sending and receiving data through cable or wireless medium.

Data Link:
It packages raw bits into frames and incorporates CRC in the frames. It takes care of errors in the physical layer. It provides flow control and also does frame synchronization. ARQ is implemented to take care of retransmission in case of erroneous packets. MAC takes care of resource assignment to the end devices wanted to seek connection to the network for various applications (voice, data, etc.)

Network:
The main function is switching and routing of the packet. It adds logical addressing to do this. It also takes care of error handling, congestion control and packet sequencing.

Transport:
It assures reliable data communication between two hosts. It is responsible for error recovery and flow control between two hosts. It also does multiplexing and de multiplexing functionalities for transmitting and receiving host respectively.

Session:
It Provides control mechanism to connect two applications running on different machines. It covers basic function to establish, to maintain and to release connections.

Presentation:
It formats and encrypts data to be sent across a network. Its basic task is to make application layer and network layer talk to each other by processing the data. It provides independence to the application processes from differences in data representation by way of syntax conversion.

Application:
All the applications for user reside at this layer. It includes FTP, Telnet, e-mail etc.
Refer basics of OSI and TCP-IP layers for more information.

Benefits or advantages of OSI Model

Following are the benefits or advantages of OSI Model:
➨It distinguishes very clearly between services, interfaces and protocols. Hence devices or equipments from different vendors can work together in the single network unlike proprietary systems.
➨As mentioned above, each layer defines a set of functions in data communication. As a result troubleshooting is easier.
➨The protocols in OSI model are hidden and hence they are easily replaced by new protocols and changes in the protocols.
➨OSI model is truly general model which is very easy to adopt by equipment/device manufacturers.
➨This model supports connection oriented and connectionless services.

Drawbacks or disadvantages of OSI Model

Following are the drawbacks or disadvantages of OSI Model:
➨Many of the applications do not require data integrity provided by OSI model.
➨OSI model is too complex compare to TCP/IP which is more optimized and effective. Session and presentation layers are hardly used. Data link layer and network layer funtionalities are split into several layers.
➨Connection mode transfer in OSI model requires agreement between three parties viz. users and service provider. Hence it is slow.
➨OSI model is not adopted for all the telecommunication applications used on the computer.
➨Due to complexity of model, initial implementations were time consuming and slow.

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