Open System Interconnection Model is commonly known as the OSI/ISO Model. It was developed by the ISO (International Organization for Standardization). It is a standard model for networking protocols and distributed applications


OSI model is a standard for communication that basically defines a networking framework; it’s a set of protocols that identify and regulates all the data communication practices. Most of the network communications used these days are structured on the basis of the OSI model.


Information from an application in a computer is transmitted which is then received on to an application in another computer through a network medium, the OSI model segregates this communication process or tasks into seven different layers, by passing the control from one layer to the other. At the senders station the control of the data flow starts from the application layer and then working down through the model where as at the receivers station control is then back up to the top layer.


Each layer of the OSI model functions on the principle of providing services to the top layer and obtaining services from the bottom layer.

Seven layers of the OSI model are divided into two basic groups or sets: The Upper Layers or The Application set and The Lowers Layers or The Transport set.

The Application Set:

This set includes layer 7, 6 and 5; these layers handles all the application based functions (data encryption, formatting etc).

The Transport Set:

This set includes layer 4, 3, 2 and 1; these layers handles all the data transport functions (Data routing, addressing and flow control etc).

The seven distinct layers of the OSI model are as follows:

1. Physical-

This layer carries the raw bit stream through the network it corresponds to basic network hardware.

2. Data Link-

This layer organizes data into frames and then delivers these frames between the sending and the receiving party.

3. Network-

This layer routes the packets (information) through out the network and determines that how the data will be transmitted between the network devices.

4. Transport-

This layer provides data transfer between the communicating parties; it’s responsible for flow of control and error free data recovery, in short handles all the end to end connection details.

5. Session-

This layer establishes, manages and then terminates a communication session.

6. Presentation-

This layer encrypts decrypts compresses and formats the data and ensures that the data is readable.

7. Application-

This layer specifies how one particular application uses a network.


There are many advantages of using the OSI model but the two most important benefits are:

OSI model does not depend on the operating system; that is why different operating systems using the OSI model can easily communicate with one another.
If errors occur in any layer then they can be detected and handled; as error checking schemes are implemented at each layer of the OSI model.


Joe Spoto is a senior lecturer at Commsupport networks CCNA training
in the United Kingdom. Joe teaches Cisco CCNA, CCNP, CCVP courses when he is not out on the road fixing and building networks, if you want to find out more about what we do at Commsupport please visit us at CCNA Course

Commsupport run free one day training sessions and free on-line webinars, CCNA training

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