← IGCSE Computer Science Paper 1

Why compression is needed: less bandwidth

A compressed file has fewer bits to send, so it uses less of the shared network bandwidth. This eases congestion and helps video and audio stream smoothly.

Part of: IGCSE Computer Science 0478 — 1.3 Data Storage and Compression — Module 31, ACARA Digital Technologies Years 9–10 — Data Compression — Module 13, QCE Digital Solutions Unit 4 — Digital Methods for Exchanging Data — Module 53

Understanding Why compression is needed: less bandwidth in IGCSE Computer Science Paper 1

What it does: Compressing the video first reduces the bits sent per second, so the stream needs less bandwidth and buffers less. Smaller compressed files take up less of the shared bandwidth, which eases network congestion for everyone.

Common mistakes: An IF statement needs THEN after the condition. The line should be IF compressed = TRUE THEN. Compression should make the file smaller, so the bits to send must be divided, not multiplied. It should be size_bits ← size_bits / 2.

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This module's key terms are also in a printable crossword (Modules 86–109) and word search (Modules 86–120).

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Learning
Duo
Why does compressing a file use less bandwidth when it is sent over a network?
Fewer bits have to be sentThe bits travel faster along the cable
Matches
Compression makes a file bigger, so it needs more bandwidth to send
↓
Compression reduces the number of bits in a file. Fewer bits use less bandwidth, not more.
Applying
Meanings
Term
compression saves bandwidth
Meaning
A compressed file has fewer bits to send, so it uses less of the shared network bandwidth. This eases congestion and helps video and audio stream smoothly.
Practice
videoBits ← 80000000
Testing
Gaps
A compressed file has fewer to send
Check Answer
Spots
1IF compressed = TRUE
2 bits_sent ← 4000000

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Quick Questions

1. Why does compressing a file use less bandwidth when it is sent over a network?
A. Fewer bits have to be sent ✓
B. The bits travel faster along the cable
Compression reduces the number of bits in the file. Fewer bits to send means less bandwidth is used. It does not change the speed of the cable.
2. Ten students in a school share one internet connection. Which statement is true?
A. Each student gets their own separate bandwidth that others cannot use
B. Bandwidth is shared, so smaller files leave more for everyone ✓
Bandwidth is shared between users. If one user sends compressed files, more of it is left for the other users.
3. A video is compressed before it is streamed. What is the benefit?
A. It uses less bandwidth, so it is less likely to buffer ✓
B. It uses more bandwidth, so the picture is sharper
Compressed video has fewer bits to send, so it can stream more smoothly with less buffering.
4. Which is the best description of network congestion?
A. A file being compressed to a smaller size
B. Too much data trying to use the network at once ✓
Congestion happens when too much data is sent at the same time. Compressing files reduces the data sent and helps ease it.
5. What effect does compressing many files have on network congestion?
A. It reduces congestion ✓
B. It increases congestion
Smaller files mean fewer bits on the network, so there is less congestion.

Match the Pairs

compression saves bandwidth → A compressed file has fewer bits to send, so it uses less of the shared network bandwidth.
bandwidth → The amount of data that can be sent over a network connection in a given time, shared between all the users.
A video is compressed before streaming, so fewer bits are sent and it plays smoothly without buffering → stream(compress(video))
Compressing files before sending them means less congestion because many users share the same network → send(compress(file))
Compression makes a file bigger, so it needs more bandwidth to send → Compression reduces the number of bits in a file. Fewer bits use less bandwidth, not more.
Only one user can use the bandwidth, so compression has no effect on other users → Bandwidth is shared between users. A compressed file uses less of it and leaves more for others, reducing congestion.

Key Term

compression saves bandwidth
A compressed file has fewer bits to send, so it uses less of the shared network bandwidth. This eases congestion and helps video and audio stream smoothly.

Fill in the Blanks

1. A compressed file has fewer bits to send
Hint: Type the smallest unit of data that is sent over a network
2. Bandwidth is shared between network users
Hint: Type the word that describes how users divide the bandwidth between them
3. Less data sent means less congestion
Hint: Type the network problem that happens when too much data is sent at once
4. Streaming video and audio use compression so they play without buffering
Hint: Type the technique that makes files smaller so they stream smoothly
5. A compressed file uses less bandwidth
Hint: Type the word that compares the bandwidth used with an uncompressed file

Spot the Error

Question 1
A IF compressed = TRUE
B bits_sent ← 4000000
C ELSE
D bits_sent ← 8000000
E ENDIF
Line A — An IF statement needs THEN after the condition. The line should be IF compressed = TRUE THEN.
Question 2
A bandwidth ← 2000000
B size_bits ← 8000000
C IF compressed THEN
D size_bits ← size_bits * 2
E ENDIF
F OUTPUT size_bits / bandwidth
Line D — Compression should make the file smaller, so the bits to send must be divided, not multiplied. It should be size_bits ← size_bits / 2.
Question 3
A video_bits ← 5000000
B bandwidth ← 2000000
C IF video_bits > bandwidth THEN
D OUTPUT "Video plays"
E ELSE
F OUTPUT "Video plays"
Line D — If the video needs more bits than the bandwidth can carry, it will buffer. The output should be "Video buffers".
Question 4
A bandwidth ← 100 // Mbps, 4 users
B share ← bandwidth * 4
C OUTPUT share
Line B — Bandwidth is shared between users, so each user gets the total divided by the number of users. It should be share ← bandwidth / 4.
Question 5
A WHILE streaming = FALSE
B chunk ← compress(chunk)
C SEND chunk
D ENDWHILE
Line A — The loop must keep compressing and sending while the video is streaming. The condition should be streaming = TRUE.

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