Protocol layers and service models

The vertical view of the Internet considers a different problem of communication:

  • How is an email is eventually translated into bits and sent to the network media?
  • How can we guarantee that the email is received, even if the communication channel is noisy and prone to errors?
  • Can a huge piece of information (for example, a streaming video) be sent in just a single packet or should it be fragmented to prevent the link from collapsing?

Basically, a communication protocol needs to be defined, analogously to the human language.

A conversation between two people could be: Hello! Hi! What is you name? Alice. This is analogous to network communication protocols, where a computer wants to retrieve some piece of information of some other. In this case, the conversation would be a exchange of message like this: TCP connection request.  TCP connection reply. GET uah.es/file.  Message containing the file requested

However, just a single protocol might be too complex to translate an email into bits. For this reason, the design is divided into protocol layers:

  • Communication functions are divided into a number of modules or layers
  • Network design is simplified:
    • “Big problem” is fragmented in simpler problems
      • → "divide and conquer”
    • Layered design makes things easier
    • The OSI model defines 7 layers
    • The Internet (practical) model reduces it to 5 layers
      • → The TCP/IP stack
Picture showing an example of protocol layers. Each layer is connected vertically to the closest levels (Layer 4 is connected to 5 and 3), and it can communicate horizontally with other instances of the same layer via a specific protocol (for example, Layers 4 in different devices would use the same protocol for communication).
UHI logo

All efforts have been made to ensure materials created by the EDU comply with current accessibility guidelines (JISC: Support for learners with disabilities).

If further assistance is required with accessibility matters please contact the student support section in your academic partner UHI: Accessing learner support.

We welcome any comments on how to improve this unit. Please feel free to pass these on at any time.

If you have any difficulty viewing this resource please contact EDU (edu@uhi.ac.uk) with:

  • the name of the resource;
  • a description of the problem (please give as much detail as possible);
  • the section of the resource where the problem occurred;
  • your internet browser (you can check your browser version at: http://detectmybrowser.com/).

UHI provides links to external sources of information and may refer to specific Web sites, products, processes or services within this resource. Such references are examples and are not endorsements and whilst every effort is taken to ensure the accuracy of information provided UHI is not responsible for any of the content or guidance. You are advised to exercise caution.

Audio

Video

Reading

Download

Information

External link

Activity

Print

Question

Asterisk

Discussion

Collaboration

Reflection/journal/log

History

Pause for thought

Download a copy of this resource in PDF format.

You can also print individual pages by printing directly from the browser.

×