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IGCSE · Practice questions · Packets and packet switching

Many routes, one message.

Six original Cambridge-style questions on packets and packet switching, with mark-point solutions.

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

Header, payload, trailer.

01
Recall
[3 marks]

Identify the three items of data stored in a packet header.

  • Destination address. ✓
  • Originator's (sender's) address. ✓
  • Packet number. ✓
02
Recall
[2 marks]

State what is stored in the payload and in the trailer of a packet.

  • Payload: the actual data being transmitted. ✓
  • Trailer: an end of packet marker and/or an error check such as a checksum. ✓
03
Explain
[5 marks]

Describe the process of packet switching when a file is sent from one computer to another across the internet.

  • The file is broken down into packets. ✓
  • Each packet is given a header including a packet number and the destination address. ✓
  • Each packet could take a different route. ✓
  • Routers control the route each packet takes. ✓
  • Packets may arrive out of order; once the last packet arrives they are reordered using the packet numbers. ✓
04
Explain
[2 marks]

Explain why the packets of one file may arrive at the destination in a different order from the order they were sent.

  • Each packet can take a different route. ✓
  • Some routes are longer or busier (more traffic), so a packet sent later can arrive earlier. ✓
05
Apply
[2 marks]

A video file is sent as 500 packets. Packet 237 is corrupted on the way. Explain one advantage of packet switching in this situation.

  • Only packet 237 needs to be resent. ✓
  • The other 499 packets do not need to be sent again, saving time and bandwidth. ✓
06
Analysis
[2 marks]

A student says: "The receiving computer uses the originator's address to reorder the packets." Explain why this is wrong.

  • Every packet from the file has the same originator's address, so it cannot show the order. ✓
  • The packet number in the header is used to reorder the packets. ✓

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.