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Networking Fundamentals · Foundational

Open Systems Interconnection Model (OSI model)

A seven-layer ISO reference model that describes how data moves from an application on one host to an application on another.

Definition

The OSI model, published as ISO/IEC 7498-1, divides network communication into seven layers: Physical, Data Link, Network, Transport, Session, Presentation and Application. Each layer provides services to the layer above and relies on the layer below. It is a conceptual reference used for teaching, design and troubleshooting rather than a protocol suite that is implemented directly.

Example

A mnemonic from Layer 1 up is "Please Do Not Throw Sausage Pizza Away."

Exam tip

Expect questions that give a device, protocol or PDU and ask for its layer, so memorize both the layer numbers and names in each direction.

Don't confuse it with

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