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A2 · Practice questions · The TCP/IP protocol suite

Down the stack and up.

Six original Cambridge-style questions on protocols and the TCP/IP suite, with mark-scheme style solutions.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

One job per layer.

01
Explain
[2 marks]

Explain why a protocol is essential for communication between two computers.

  • A protocol is a set of rules for transmitting data (format, addressing, error checking, timing). ✓
  • Both devices must follow the same rules so they interpret the data in the same way, even if they are from different manufacturers or use different operating systems. ✓
02
Recall
[4 marks]

Name the four layers of the TCP/IP protocol suite, in order from the top.

  • Application ✓
  • Transport ✓
  • Internet ✓
  • Link ✓
03
Explain
[3 marks]

Explain why the implementation of a protocol suite can be viewed as a stack.

  • The protocols are arranged in layers, each with its own function. ✓
  • Each layer only communicates with the layer directly above and below it / receives data from the layer above and passes it to the layer below. ✓
  • So a layer can be changed or replaced without affecting the others. ✓
04
Explain
[4 marks]

Describe the function of the Transport layer when data is sent and received using TCP.

  • Splits the data from the Application layer into segments. ✓
  • Adds a header with source and destination port numbers and a sequence number. ✓
  • At the receiver, uses the sequence numbers to reassemble the segments in order. ✓
  • Sends acknowledgements / requests retransmission of lost segments (reliable delivery). ✓
05
Calculate
[2 marks]

A file of 10 000 bytes is sent using TCP. Each segment can carry a maximum of 1460 bytes of data. Calculate how many segments are needed and the number of data bytes in the final segment.

  • 10 000 / 1460 = 6.85, so 7 segments are needed. ✓
  • 6 x 1460 = 8760; 10 000 - 8760 = 1240 bytes in the final segment. ✓
06
Apply
[5 marks]

A user clicks a link in a web browser. Describe how the request is passed through the TCP/IP layers on the user's computer before it is sent.

  • Application layer: the browser creates an HTTP request (GET) for the page. ✓
  • Transport layer: TCP sets up a connection with the server and splits the request into segments. ✓
  • Transport layer: adds port numbers and a sequence number to each segment. ✓
  • Internet layer: IP adds the source and destination IP addresses to form packets. ✓
  • Link layer: adds MAC addresses to form frames and transmits them as signals on the medium. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.