← ACARA Digital Technologies Years 9–10

User Datagram Protocol (UDP)

User Datagram Protocol: sends packets with no connection and no resending. It is faster than TCP but data may be lost, so it suits live video, voice calls and online games.

Part of: ACARA Digital Technologies Years 9–10 — Networked Systems and Access Control — Module 53, QCE Digital Solutions Unit 4 — Digital Methods for Exchanging Data — Module 92, WA Computer Science ATAR Year 11 — Network Communications — Module 53, WA Computer Science ATAR Year 11 — Cyber Security — Module 22

Understanding User Datagram Protocol (UDP) in ACARA Digital Technologies Years 9–10

What it does: Games and live video or voice care more about speed than perfect delivery, so UDP is the better choice. UDP just sends the packets. TCP sets up a connection first. UDP has no resending, so lost packets stay lost. Asking for a resend is what TCP does. UDP never waits for the receiver to say a packet arrived, which is part of why it is fast. Less work means less delay. The cost is that some data may be lost. UDP favours speed. TCP favours reliability. A game needs fast updates, and a missed update is soon replaced by a newer one. A file download needs every packet, so TCP is better.

Common mistakes: UDP does not resend lost packets. The line should be resend_lost ← false. UDP suits live video, voice and games, where speed matters most. Email needs every part to arrive, so it uses TCP. The condition should be task = "live video".

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This module's key terms are also in a printable crossword (Modules 41–55) and word search (Modules 12–55).

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Learning
Duo
Which protocol sends packets without first setting up a connection?
UDPTCP
Matches
UDP resends any lost packet
↓
UDP does not resend lost packets. It has no acknowledgements, so lost data is simply gone. Resending is what TCP does.
Applying
Meanings
Term
UDP
Meaning
User Datagram Protocol: sends packets with no connection and no resending. It is faster than TCP but data may be lost, so it suits live video, voice calls and online games.
Practice
task ← "online game"
Testing
Gaps
SET protocol TO
Check Answer
Spots
2connection ← false
3resend_lost ← true

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Quick Questions

1. Which protocol sends packets without first setting up a connection?
A. TCP
B. UDP ✓
UDP just sends the packets. TCP sets up a connection first.
2. A packet is lost while using UDP. What happens?
A. It is not resent, so the data is missing ✓
B. UDP asks for it to be sent again
UDP has no resending, so lost packets stay lost. Asking for a resend is what TCP does.
3. Which statement about UDP is true?
A. The receiver sends an acknowledgement for every packet
B. It does not use acknowledgements ✓
UDP never waits for the receiver to say a packet arrived, which is part of why it is fast.
4. Why is UDP usually faster than TCP?
A. It skips connection setup and resending ✓
B. It checks and resends every lost packet
Less work means less delay. The cost is that some data may be lost.
5. What is the trade-off of choosing UDP over TCP?
A. More speed but less reliability ✓
B. More reliability but less speed
UDP favours speed. TCP favours reliability.

Match the Pairs

UDP → User Datagram Protocol: sends packets with no connection and no resending, so it is fast but some data may be lost
TCP → The reliable protocol that sets up a connection and resends lost packets, but is slower than UDP
A live online game needs fast updates and can ignore a lost packet, so it should use the fast, no-resend protocol → protocol = UDP
Downloading a file needs every packet to arrive, so it should use the protocol that acknowledges and resends → protocol = TCP
UDP resends any lost packet → UDP does not resend lost packets. It has no acknowledgements, so lost data is simply gone. Resending is what TCP does.
Use UDP to send a bank transfer because it is faster → A bank transfer cannot afford lost data, so it needs reliable TCP. UDP is only suited to live video, voice and games where speed matters more.

Key Term

UDP
User Datagram Protocol: sends packets with no connection and no resending. It is faster than TCP but data may be lost, so it suits live video, voice calls and online games.

Fill in the Blanks

1. SET protocol TO UDP
Hint: Type the short name of the protocol that sends packets with no connection.
2. IF task = "file download" THEN use TCP
Hint: Type the protocol that checks packets arrived and resends lost ones, so no data is lost.
3. resendLost ← FALSE
Hint: Type the Boolean value that shows UDP never resends lost packets.
4. UDP sends no acknowledgements to the sender
Hint: Type the word for the replies that confirm packets arrived, which UDP does not send.
5. Speed: UDP is faster, TCP is more reliable
Hint: Type the quality TCP offers because it resends lost data, which UDP does not.

Spot the Error

Question 1
A protocol ← "UDP"
B connection ← false
C resend_lost ← true
Line C — UDP does not resend lost packets. The line should be resend_lost ← false.
Question 2
A IF task = "email" THEN
B protocol ← "UDP"
C ELSE
D protocol ← "TCP"
E ENDIF
Line A — UDP suits live video, voice and games, where speed matters most. Email needs every part to arrive, so it uses TCP. The condition should be task = "live video".
Question 3
A FOR each frame IN video
B SEND frame by UDP
C WAIT for ACK
D NEXT
Line C — UDP has no acknowledgements, so the sender does not wait for a reply. The line should say not to wait for an ACK.
Question 4
A speed_UDP ← "fast"
B speed_TCP ← "slower"
C reliability_UDP ← "high"
D reliability_TCP ← "high"
Line C — UDP is faster but less reliable than TCP because it never resends lost data. The reliability of UDP should be "low".
Question 5
A IF packet is lost THEN
B ask sender to resend it
C ELSE
D play the packet
E ENDIF
Line B — UDP never asks for lost packets to be sent again. It skips them and carries on, so the line should be skip it and carry on.

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