Computer Networking › Section A · Computer networks and the internet › Topic A.5

Protocol layers and encapsulation

The internet runs hundreds of protocols on billions of different devices. Layering is the idea that keeps this manageable: each layer does one job for the layer above it, and encapsulation is how the layers cooperate on every single packet.

In this topic

  • Why build a network in layers
  • Service models and peer protocols
  • The top two layers
  • The bottom three layers
  • The OSI model and layer numbers
  • Encapsulation
  • Worked example: the cost of headers
  • Which devices run which layers
  • Worked example: one frame's journey
  • The costs of layering
  • Common mistakes to avoid
  • Key takeaways

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