← ACARA Digital Technologies Years 7–8

Latency

The delay between sending data and it arriving, measured in milliseconds (ms). It is not the same as bandwidth, which is how much data can be sent at once. Low latency feels fast.

Part of: ACARA Digital Technologies Years 7–8 — Wired and Wireless Networks — Module 21, QCE Digital Solutions Unit 4 — Digital Methods for Exchanging Data — Module 86, WA Computer Science ATAR Year 11 — Network Communications — Module 15

Understanding Latency in ACARA Digital Technologies Years 7–8

What it does: Bandwidth is how much data can be sent at once, while latency is the delay. A link can be wide but still slow to respond, like a satellite connection. A low latency means a small delay, so button presses reach the server quickly and the game feels smooth. Latency is a time, so it is measured in milliseconds. Megabytes measure an amount of data. Ping time is a latency measurement. The second answer describes bandwidth. Shorter routes mean less delay. Sending bigger files does not make each message arrive sooner.

Common mistakes: Latency is a delay measured in milliseconds (ms), not Mbps. Mbps is a unit for bandwidth. The variable should be named latency_ms. The else line needs a colon at the end. It should be else:.

Class: _____________________  ·  Name: _____________________  ·  Date: _________

Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

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This module's key terms are also in a printable crossword (Modules 54–68) and word search (Modules 13–68).

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Learning
Duo
What does latency measure?
How much data can be sent at onceThe delay between sending data and it arriving
Matches
latency = 40 Mbps
↓
Latency is measured in milliseconds (ms), not Mbps. Mbps is a unit for bandwidth.
Applying
Meanings
Term
latency
Meaning
The delay between sending data and it arriving, measured in milliseconds (ms). It is not the same as bandwidth, which is how much data can be sent at once. Low latency feels fast.
Practice
bandwidth <- 100
Testing
Gaps
example.com
Check Answer
Spots
1latency_ms = 20
2latency_mbps = 20

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Quick Questions

1. What does latency measure?
A. How much data can be sent at once
B. The delay between sending data and it arriving ✓
Latency is delay. How much data can be sent at once is bandwidth.
2. Which unit is latency usually measured in?
A. Milliseconds (ms) ✓
B. Megabytes (MB)
Latency is a time, so it is measured in milliseconds. Megabytes measure an amount of data.
3. A ping test shows 20 ms. What does this number tell you?
A. It took 20 milliseconds for a small message to travel and get a reply ✓
B. The network can carry 20 megabits of data every second
Ping time is a latency measurement. The second answer describes bandwidth.
4. Which connection has the lower latency, and so feels faster to react?
A. Ping of 250 ms
B. Ping of 15 ms ✓
A smaller delay means lower latency. Low latency feels fast.
5. Is this statement true? A connection can have high bandwidth and high latency at the same time.
A. True: lots of data can be sent at once, but each piece still arrives after a long delay ✓
B. False: high bandwidth always means low latency
Bandwidth and latency are different. A satellite link can carry lots of data but still have a long delay.

Match the Pairs

ping 8.8.8.8 -> time=24 ms → A ping test shows the round-trip delay, or latency, to another computer. Here the delay was 24 milliseconds.
latency = 300 ms → A high delay between sending data and it arriving, which makes video calls and online games lag.
Latency is not the same as bandwidth: you can have a high bandwidth link with high latency. → bandwidth = 500 Mbps; latency = 600 ms
Online games need low latency so your moves reach the server quickly. → if latency < 50: game = 'smooth'
latency = 40 Mbps → Latency is measured in milliseconds (ms), not Mbps. Mbps is a unit for bandwidth.
High bandwidth always means low latency, so a video call will never lag. → Bandwidth and latency are different. A connection can have high bandwidth and still have high latency, which causes lag in video calls.

Key Term

latency
The delay between sending data and it arriving, measured in milliseconds (ms). It is not the same as bandwidth, which is how much data can be sent at once. Low latency feels fast.

Fill in the Blanks

1. ping example.com
Hint: Type the network command that measures the round-trip delay to a server.
2. IF latency < 50 THEN OUTPUT "Smooth"
Hint: Type the comparison operator that means lower than, since a low delay is good.
3. latency = arriveTime - sendTime
Hint: Type the variable holding the moment the data left, to work out the delay.
4. IF latency > 150 THEN OUTPUT "Laggy"
Hint: Type the variable that measures the delay, because that is what makes a game feel laggy.
5. lagging = bandwidthHigh AND latencyHigh
Hint: Type the logical keyword that needs both conditions to be true.

Spot the Error

Question 1
A latency_ms = 20
B latency_mbps = 20
C print(latency_ms, "ms")
Line B — Latency is a delay measured in milliseconds (ms), not Mbps. Mbps is a unit for bandwidth. The variable should be named latency_ms.
Question 2
A ping_ms = 120
B if ping_ms > 100:
C print("Game lags")
D else
E print("Smooth")
Line D — The else line needs a colon at the end. It should be else:
Question 3
A latency = 40
B bandwidth = 500
C print("Latency:", latency)
D print("Bandwidth:", latency)
Line D — This line is labelled Bandwidth but prints the latency variable. Latency and bandwidth are different measures. It should print bandwidth.
Question 4
A delay_ms = "300"
B if delay_ms > 150:
C print("Video call lags")
Line A — The quotes make 300 a string, so it cannot be compared with the number 150. The delay should be a number: delay_ms = 300
Question 5
A ping_ms = 30
B if ping_ms < 50:
C print("High latency")
Line C — A ping time of 30 ms is below 50, so it is low latency. The message should say Low latency, not High latency.

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