What is the OSI model?

The Open Systems Interconnection (OSI) model is used to understand how data is transmitted across devices that are connected via a network (regardless of their underlying technology). In other words, the OSI model standardizes data networking protocols to allow all networked devices to communicate.

The OSI model breaks down the data transfer procedure into seven layers. Each layer provides a service to the layer on top of it and uses the services provided by the layer below it. Changes in one layer do not affect the other layers ​provided that the interface remains the same.

The following are the seven layers in the OSI model:

Let’s go over each layer:

Application layer:

The application layer is used by applications to transmit data. It includes protocols like HTTP (hyper-text transfer protocol) and SMTP (simple mail transfer protocol).

Presentation layer:

Data from the application layer is passed on to the presentation layer. It converts this data into binary language, compresses it, and encrypts/decrypts it.

Session layer:

The session layer manages sessions between the communicating devices. Sessions are opened and terminated by the session layer.

Transport layer:

The transport layer determines how much data should be sent at a time, and deals with congestion control and the reliable delivery of data.

Network layer:

Every device on the network has a unique IP address. The network layer delivers data packets across the network using these unique IP addresses. Routers reside on this layer.

Data Link layer:

​ The data link layer sends packets across machines that are residing on the same media. Switches operate at this level.

Physical layer:

Data is converted into signals and transmitted across two devices connected via a physical medium. Upon receiving a signal, the physical layer converts the data ​into bits.