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Layers

Computer Science: OCR GCSE, topic 1.3.25

Layering Concepts

Protocol layer models are often used to help conceptualise the many different network protocols.

Protocol layer models

Protocol layer models

  • In a protocol layer model, a protocol layer is simply a group or collection of network protocols that work at a similar level within the networking process.
Layer properties

Layer properties

  • Layers of a protocol layer model should be independent of each other.
  • Layers should only interact with each other by considering the inputs and outputs of that layer, not how it works.
Layers everywhere

Layers everywhere

  • Layers are not only used within networking.
  • Layers are one example of a technique called abstraction, which helps to simplify problems.
  • Layers are commonly used in software development. For example:
  • A user interface layer.
  • A processing layer.
  • A database layer.

TCP and OSI Models

The four-layer Transmission Control Protocol model and the seven-layer Open Systems Interconnection model are two of the best known protocol layer models.

TCP model

TCP model

  • Application layer:
  • Creates and interprets data (e.g. HTTP, IMAP, FTP).
  • Transport layer:
  • Splitting / joining of data (e.g. TCP).
  • Internet layer:
  • Adding addresses to data (e.g. IP).
  • Network Access layer:
  • Converting data into electrical signal (hardware) (e.g. Ethernet, WiFi).
OSI model

OSI model

  • The OSI model is a very similar protocol layer model.
  • The OSI model has seven layers:
  • Application.
  • Presentation.
  • Session.
  • Transport.
  • Network.
  • Data Link.
  • Physical.
Comparing the two models

Comparing the two models

  • The two models describe the exact same network system:
  • The first three layers of the OSI model are grouped into TCP's 'Application' layer.
  • The 'Transport' layers are the same in both models.
  • OSI's 'Network' layer is called 'Internet' in the TCP model.
  • OSI's bottom two layers are combined into TCP's 'Network Access' layer.

Test yourself on Layers

  • Which of these should a layer consider about other layers?

  • Are layers used only in networking?

  • Transmission Control Protocol Model

  • Open Systems Interconnection Model

  • What is the difference between the TCP and OSI models?

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