What is the OSI model?

The Open System Interconnection (OSI) model defines a networking framework to implement protocols in seven layers. Use this handy guide to compare the different layers of the OSI model and understand how they interact with each other.

The OSI model is a conceptual framework so we can better understand complex interactions that are happening.

Who Developed the OSI Model?

The International Standards Organization (ISO) developed the Open Systems Interconnection (OSI) model. It divides network communication into seven layers. Layers 1-4 are considered the lower layers, and mostly concern themselves with moving data around. Layers 5-7, the upper layers, contain application-level data. Networks operate on one basic principle: “pass it on.” Each layer takes care of a very specific job and then passes the data onto the next layer.

See diagrams to the right that explains the 7 OSI Levels.

Why you need to know the 7 OSI layers

Most people in the IT space will likely need to know about the different layers when they’re going for their certifications, much like a civics student needs to learn about the three branches of the U.S. government. After that, you hear about the OSI model when vendors are making pitches about which layer(s) their products work with.

“The purpose of the OSI reference model is to guide vendors and developers so the digital communication products and software programs they create will interoperate, and to facilitate clear comparisons among communications tools.”

If you can understand the OSI model and its layers, you can also then understand which protocols and devices can interoperate with each other when new technologies are developed and explained.

Remembering the OSI Model 7 layers – 8 mnemonic tricks

If you need to memorize the layers for a college or certification test, here are a few sentences to help remember them in order. The first letter of each word is the same as a layer of the OSI model.

From Application to Physical (top down):

1. All People Seem To Need Data Processing
2. All Pros Search Top Notch Donut Places
3. A Penguin Said That Nobody Drinks Pepsi
4. A Priest Saw Two Nuns Doing Pushups

 From Physical to Application (bottom up):

1. Please Do Not Throw Sausage Pizza Away
2. Pew! Dead Ninja Turtles Smell Particularly Awful
3. People Don’t Need To See Paula Abdul
4. Pete Doesn’t Need To Sell Pickles Anymore