What is the OSI Model

Open Systems Interconnect (OSI) Model

The International Standards Organization (ISO) developed a theoretical model of how networks should behave and how they are put together. This model is called the Open Standards Interconnect (OSI) Model.

The OSI Model is a theoretical, seven-layered model of how networks work. The OSI Model is a theoretical model of networking that organizes network functions into seven layers,

Physical layer
Datalink layer
Network layer
Transport layer
Session layer
Presentation layer
Application layer

It specifies the communication interfaces between the OSI Model's layers and between network endpoints utilizing an OSI Model-based protocol suite.

The OSI Model is a way of thinking about how networks work.

The OSI Model is a theoretical model

The OSI Model is not a technology.
The OSI Model is not a protocol.
The OSI Model is not a program or software.

The OSI Model sorts network communication functions into seven layers.

Layer functions are not specified and should be transparent to other layers.
Layer Communications (how layers communicate with each other) ARE specified in the model
Layer behavior should be invisible to other layers

The OSI Model was developed as the ISO designed their own suite of networking protocols (the ISO OSI Protocol Suite). The OSI Model is always in the middle of any discussions of networking and network and sometimes computer troubleshooting. The OSI model is used so commonly as a point of reference that you really should learn the OSI Model's seven layers and learn how the OSI Model explains this layered approach to networking.

Engineers working on a network problem will frequently say "Well, it's a data link layer problem", clearly referring to the data link layer of the OSI Model and more specifically, the physical network connection, not the networking software or the applications. The OSI Model's layers are so well known that they are referred to by number: "Well, looks like we have a layer 2 problem here". If you don't know the OSI Model, you will have great difficulties as a network engineer, or even talking to one.

See also,

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