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The TCP/IP Model and Network Layers

FoundationHigherAQA

Practise The TCP/IP Model and Network Layers for GCSE Computer Science with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers. Network communication is organised into four layers, each handling part of the process.

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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA specification. Every worksheet comes with a full mark scheme.

Foundation

WorksheetFoundation · PDFMark SchemeFoundation · PDF

Higher

WorksheetHigher · PDFMark SchemeHigher · PDF

Topic overview

The TCP/IP model organises network protocols into four layers, each with its own responsibility.

The application layer handles the protocols the user's software uses, such as HTTP and SMTP. The transport layer, using TCP, breaks data into packets and reassembles them in order at the destination. The internet layer, using IP, addresses packets and routes them across the network. The link layer handles the physical transmission over the cable or wireless connection.

Layering matters because each layer can be changed without affecting the others. Switching from wired to wireless changes the link layer only — the application layer is untouched, so the software needs no modification at all.

Revision notes

The four layers

Application: protocols the user's software uses, such as HTTP, SMTP and FTP.

Transport: TCP breaks data into packets and reassembles them in order. Internet: IP addresses and routes packets. Link: physical transmission over cable or wireless.

Why layering helps

Each layer can be changed without affecting the others.

Switching from wired to wireless changes only the link layer; the application layer is untouched, so software needs no modification. This is the key benefit and is examined directly.

Packets

Data is broken into packets before transmission and reassembled at the destination.

Each packet carries the destination address and a sequence number, so packets arriving out of order can be put back in the right sequence.

Key points

  • The TCP/IP model has four layers.
  • The application layer handles user protocols.
  • The transport layer breaks data into packets.
  • The internet layer addresses and routes packets.
  • The link layer handles physical transmission.
  • Layers can be changed independently.

Worked examples

Example 1

Name the four layers of the TCP/IP model in order. [2 marks]

Working

Application layer, then transport layername the first two
then internet layer, then link layername the remaining two

Example 2

Explain one benefit of organising protocols into layers. [2 marks]

Working

Each layer can be changed without affecting the othersstate the benefit
so switching from a wired to a wireless connection changes only the link layer, leaving the software unaffectedgive an example

Example 3

State which layer breaks data into packets and what else it does. [2 marks]

Working

The transport layername the layer
It also reassembles the packets in the correct order at the destinationstate its other function

Common mistakes

  • Getting the layer order wrong.

    Application, transport, internet, link.

  • Confusing the transport and internet layers.

    Transport handles packets; internet handles addressing and routing.

  • Not explaining the benefit of layering.

    Independent change is the point.

  • Saying packets always arrive in order.

    They may not, which is why sequence numbers exist.

Exam tips

  • Learn the four layers in order.
  • Match each layer to its protocols.
  • Explain layering through independent change.
  • Mention sequence numbers when discussing packets.

Key terms

TCP/IP model
A four-layer organisation of network protocols.
Application layer
The layer handling user software protocols.
Transport layer
The layer breaking data into packets.
Packet
A small unit of data with an address and sequence number.

Related topics

Written and reviewed against the current AQA specification. Spotted an error? Let us know.