The OSI model explained: How to understand (and remember) the 7 layer network model


When most non-technical people hear the term “seven layers”, they either think of the popular Super Bowl bean dip or they mistakenly think about the seven layers of Hell, courtesy of Dante’s Inferno (there are nine). For IT professionals, the seven layers refer to the Open Systems Interconnection (OSI) model, a conceptual framework that describes the functions of a networking or telecommunication system.

The model uses layers to help give a visual description of what is going on with a particular networking system. This can help network managers narrow down problems (Is it a physical issue or something with the application?), as well as computer programmers (when developing an application, which other layers does it need to work with?). Tech vendors selling new products will often refer to the OSI model to help customers understand which layer their products work with or whether it works “across the stack”.

Conceived in the 1970s when computer networking was taking off, two separate models were merged in 1983 and published in 1984 to create the OSI model that most people are familiar with today. Most descriptions of the OSI model go from top to bottom, with the numbers going from Layer 7 down to Layer 1. The layers, and what they represent, are as follows:

Layer 7 – Application

To further our bean dip analogy, the Application Layer is the one at the top – it’s what most users see. In the OSI model, this is the layer that is the “closest to the end user”. Applications that work at Layer 7 are the ones that users interact with directly. A web browser (Google Chrome, Firefox, Safari, etc.) or other app – Skype, Outlook, Office – are examples of Layer 7 applications.

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