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1CP2-P-7.3 Packet switching and packet structure

Part 3 of 6 · 1CP2-P-7 · Embedded systems, IoT and TCP/IP

The packet worksheet, reading the structure of a single packet and then following many of them across a network.

Students will:

  • identify the header fields that decide where a packet goes
  • describe how a file is transmitted by packet switching
  • explain why packets from one message can arrive out of order
  • explain how a checksum is used and what happens when it fails
  • explain how the receiver reconstructs the original data

Inside: 5 explanation cells, 3 multiple-choice questions, 1 fill-in-the-blanks cell and 5 written answers. 20 marks, about 45 minutes.

Series: 1CP2-P-7 · Embedded systems, IoT and TCP/IP, part 3 of 6.

Shared by Coding PathwayVerified teacher

  • 14 cells
  • About 45 minutes
  • CC BY-SA 4.0
  • Shared 17 Aug 2026

Preview

The whole resource, exactly as a class sees it. Answers and marking are held back.

Packet switching and packet structure

Large network messages are divided into smaller packets. Packet switching lets routers forward each packet across available links towards its destination. Packets may take different routes or arrive out of order, so control information is carried alongside the payload.

1. Read a packet

Packet structure and useheadersource + destinationsequence + checking datapayloadpart of original datafooterend/checkwhy fields matter• address and route• restore correct order• detect transmission errorDifferent packets can take different routes and are reconstructed at the destination.

The payload is part of the original data. Control fields support delivery and reconstruction. Examination questions may ask for header fields such as source address, destination address and packet/sequence number; error-checking information such as a checksum helps detect corruption.

Fill in the blanks3 marks
The original data carried by a packet is its gap 1. The gap 2 contains control information. A gap 3 number helps reconstruct the original order.
  • header
  • payload
  • route
  • sequence
Multiple choice1 mark

Which field is most directly used to decide where the packet must ultimately go?

  • Adestination IP address
  • Bfont size
  • Cfile extension only
  • Dscreen resolution
Written answer3 marks

State two pieces of information that may appear in a packet header and explain the purpose of one.

Use addressing, ordering or checking information.

Students type their answer here.

2. Follow packet switching

Packet switching across alternative routessourcepackets 1 · 2 · 3router Arouter Brouter Cdestinationreorders packetsrouters use destination IP address; routes can differ

A router reads addressing information and chooses a next link towards the destination. It does not need to reserve one complete end-to-end circuit. If traffic or failure changes conditions, later packets can follow another route. The destination uses ordering information to reconstruct the message.

Written answer4 marks

Describe how a file is transmitted using packet switching from source to destination.

Give the stages from splitting to reconstruction.

Students type their answer here.

Multiple choice1 mark

Why can two packets from one message arrive in a different order?

  • AEvery packet contains a different alphabet.
  • BRouters may forward them along different routes with different delays.
  • CThe payload erases the header.
  • DIP addresses change into passwords.

3. Detect and recover

Error-checking information can show that a received packet was corrupted in transmission. Transport mechanisms can request or arrange retransmission when required. A checksum detects a likely error; it does not repair the changed bits by itself.

Written answer3 marks

Explain how a checksum can be used when a packet is received and what happens if an error is detected.

Separate detection from recovery.

Students type their answer here.

Written answer2 marks

Explain one advantage of packet switching when a network link becomes unavailable.

Link independent routing to continued delivery.

Students type their answer here.

Multiple choice1 mark

Which statement is accurate?

  • AEvery packet from one message must follow the same route.
  • BA router uses addressing information to forward packets between networks.
  • CThe payload stores only the destination address.
  • DA sequence number encrypts the packet.
Written answer2 marks

Packet 3 arrives before packet 2. Explain how the receiving system can still reconstruct the original data correctly.

Use sequence information and delayed arrival.

Students type their answer here.

Route forward

You can explain packet anatomy, routing, ordering and error checking. Next you will place these responsibilities within the four-layer TCP/IP model.