OSI Model Explained | Real World Example

The OSI Model Explained

What Is this OSI Model?

The OSI model (Open System Interconnect) is a theoretical stack of 7 layers that can be used as a reference to understand how a network operates. The model was introduced to standardize networks in a way that allowed multi-vendor systems, prior to this you would only be able to have a one vendor network as the devices could not communicate with other vendor devices.

The Layers

Application (layer 7)

This layer is where the application and user communicates. Application specific protocols are used here such as SMTP (simple mail transfer protocol) for sending emails from Outlook.

Presentation (layer 6)

This layer formats the data in a way that the receiving application can understand it. This layer is also able to encrypt and decrypt date if needed.

Session (layer 5)

This layer is responsible for establishing and terminating of connections between devices.

Transport (layer 4)

The transport layer of OSI Model is used for error handling and sequencing to unsure no data is lost. This layer also adds source and destination port numbers

Network (layer 3)

The network layer handles IP address routing. At this stage of the OSI model the source and destination IP address is added to the data.

Data Link (layer 2)

At this layer the physical address (MAC Address) is added to the data, this includes the source and destination MAC address.

Physical (layer 1)

The physical layer is the lowest layer of the OSI model. Its key responsibility is to carry the data across the physical hardware such as an Ethernet cable to the destination.


This video is designed to give a basic and general overview of the OSI model. Its aim is to simplify the concept to make it easier to understand.

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