Routing & Switching
OSI Model
The OSI reference model is the seven-layer framework every networking conversation is built on. This guide walks the layers from physical signalling to application data, and shows how encapsulation actually moves a packet across a network.
- read in order, or dip in
- 2 chapters
- updated 31 Aug 2026
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read in order, or dip in
updated 31 Aug 2026
Contents
- 01The 7 Layers of the OSI Model ExplainedThe OSI model divides network communication into seven layers — Physical, Data Link, Network, Transport, Session, Presentation and Application — each with a defined job and a defined interface to the layer above and below. Engineers use it as a shared troubleshooting language: a cable fault is a layer-1 problem, a MAC issue is layer 2, a routing issue is layer 3.
- 02Encapsulation and PDUs: OSI vs TCP/IPEncapsulation is the process of wrapping data with a header at each layer as it moves down the stack: application data becomes a segment at layer 4, a packet at layer 3, a frame at layer 2 and bits at layer 1. The TCP/IP model condenses OSI's seven layers into four, and it is the model real networks actually run.
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