OSI Reference Model


Open System Interconnection model has been defined as a conceptual model used in telecommunication and computing system.

The main motive behind the development of this model is to bring about different systems and methods of communication under one standard protocol. In the Seven Layers Model, the networking system is divided into 7 layers with each layer interacting with the layer below and providing the functions to be used by the above layer. o Application - The Seventh layer is of application which the users can see and interact with directly, apps and browser are the prime examples of this.


The more simplified way to understand is to know that this layer enables human and software to interact. o Presentation - The sixth layer is for translating or formatting the data based either on the syntax or semantics based on what the application is programmed to accept and respond to. o Session - The fifth layer which is called the session layer is for starting and ending conversations between applications. You must have noticed how authentication is needed before you’re connected to a Wi-Fi network.


That’s the work assigned to this layer. o Transport - fourth layer is responsible for data transfer between the applications and across the network and also determining the amount of data that is to be sent and where it gets sent. o Network - The function of the third layer is to pack data along with the network address and hand it over to the transport layer which is the 4th layer. o Data Link - Transmission errors are handled by the second layer and to stop the overwhelming of the data transfer from harming the receiver and sender. Physical - The first layer is called the physical layer as it establishes the physical connection to the network using either electrical or mechanical interfaces.


The OSI model has been in work for over 30 years and that tells us that it is truly a reliable model. To understand this we need to learn more of its advantages. Here are some of the advantages that have not been discussed above:

1. This model transfers network in small units or as we say small components which ensures easy flow and fast functions.

2. Protocols are hidden in this model, that enables it to adapt to the other protocols that can be added later from the outside source.

3. Layers are immune to the damage that may be caused by the other layers.

4. It allows software and Hardware to communicate with each other.


However, any man-made model isn’t fault-free and there are some disadvantages in this model:

1. Being a theoretical model restrict its' implementation

2. The OSI model was launched around the same time of the launch of TCP/IP model and practically the latter model is more practical with easy implementation and has been given preference over the OSI model from the start.

3. Two layers sharing or doing one and the same function makes it a bit confusing.

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