2. Data Transmission
How data travels — serial/parallel, simplex/duplex, USB, packets, error checking and encryption.
In the 2029–31 syllabus packets and transmission methods become 3.1–3.2; error detection and encryption move into Topic 4 (Data integrity and cybersecurity). USB is removed. What changes in 2029 → · Study the new topics: 3. Data transmission and networking, 4. Data integrity and cybersecurity
Statometer84BankerNext Paper 194%Everything for this topic — study hub
O Level / IGCSE · 2210 · 0478 · Paper 1
This topic is rows 5–7 of the study route.Open it on your study route
Statometer — what 25 real papers say about this topic and each of its 3 syllabus bullets
Banker · #5 of 10 in O Level / IGCSE · recomputed with every new session
Set in nearly every paper and worth a big slice of it — revise first, expect it.
- Next Paper 1
- 94%
- 9 in 10 chance it is set
- Marks a paper
- 15.3 / 75
- 20% of Paper 1 · fair share 17%
- Appeared in
- 25 / 25
- Paper 1 sittings 2023–2026
- Last set
- May/Jun 2026
- 0478/13 · Q2 · 15 marks · 11-series streak
What the papers say
- Set in 25 of 25 Paper 1 sittings on the current syllabus — treat it as certain.
- Worth about 15.3 marks a paper (20% of Paper 1).
- Last set May/Jun 2026 · 0478/13 · Q2 for 15 marks — in the most recent series.
- Set in each of the last 11 series without a miss.
- Rising: about 14.3 marks a paper in the earlier years, 16 in the latest.
- Lives on “Explain” and “Describe” — 69% of its questions: full sentences with a reason, not one-word answers.
- 40% of its questions are set out as code, pseudocode or a table to complete.
- Most of its marks (86%) come in extended questions of 6+ marks — plan the answer before writing.
- Its biggest question so far: 24 marks (Oct/Nov 2024 · 2210/13 · Q2).
- Inside the topic, §2.1 Types and methods of data transmission carries the most marks (44%) and §2.3 Encryption the least (14%).
- It is examined mostly as AO1 (Knowledge & understanding, 63%) — definitions and descriptions in syllabus words score.
- The examiner has commented on 89 of its questions — read “What the examiner said” before you practise.
Command words
Share of questions using the word (a question can use several). What each wants →
Question shapes
- 1–2 mk1
- 3–4 mk21
- 5–6 mk21
- 7–9 mk26
- 10+ mk41
Average 8.9 marks a question · 14% with a figure or table · 40% with code · biggest 24 marks
Assessment objectives — how it is examined
Every part of every current-syllabus question filed under Cambridge's AO1 / AO2 / AO3 (from its command word and what it asks you to do), so you know whether this topic pays for definitions, for applying, or for judging and building.
- AO1 Knowledge & understanding
- AO2 Apply to a context
- AO3 Evaluate & judge
Paper 1 as a whole
| Paper 1 | Syllabus | Measured |
|---|---|---|
| AO1 Knowledge & understanding | 60% | 64% |
| AO2 Apply to a context | 20% | 24% |
| AO3 Evaluate & judge | 20% | 12% |
Syllabus = Cambridge's grid; measured = the bank's current-syllabus papers.
Inside the topic — every syllabus bullet, measured
Each part of each question is filed under the bullet it examines; the numbers are per Paper 1 sitting, exactly like the topic's. Open a bullet for its own Statometer.
2.1Types and methods of data transmission#2 of 20 on Paper 1Banker · 9089% next paper6.1 marks24/25 sittings↗ May/Jun 2026Banker · 9089%
6.1 · 44% of topic24/25May/Jun 2026latest series · ↗Asked in nearly every paper — the bullet to know cold.Syllabus: packet structure (header, payload, trailer) and packet switching; serial vs parallel; simplex, half-duplex and full-duplex; the USB interface
- Next Paper 1
- 89%
- 9 in 10
- Marks a paper
- 6.1
- 8% of the paper · 44% of the topic
- Asked in
- 24 / 25
- Paper 1 sittings · 63 questions
- Last asked
- May/Jun 2026
- 0478/13 · Q2 · 7 marks · 11-series streak
- Asked in 24 of 25 Paper 1 sittings — nearly every paper.
- About 6.1 marks a paper (8% of Paper 1; 44% of the topic's marks across its 3 bullets).
- Last asked May/Jun 2026 · 0478/13 · Q2 (7 marks) — in the most recent series.
- Asked in each of the last 11 series.
- Rising: 5.9 → 6.2 marks a paper.
- Usually “Give” or “Explain”: short, precise answers in syllabus words.
- Biggest chunk of marks so far: 14 in Oct/Nov 2025 · 2210/13 · Q3.
- It is examined as a mix: AO1 47%, AO3 29%, AO2 24% — definitions and descriptions in syllabus words score.
Last 12 sittings↗ RisingAssessment objectives
AO1 47%AO2 24%AO3 29%- AO1 Knowledge & understanding
- AO2 Apply to a context
- AO3 Evaluate & judge
- Give52%
- Explain49%
- Describe49%
- State44%
2.2Methods of error detection#13 of 20 on Paper 1Core · 5761% next paper3.6 marks15/25 sittings→ May/Jun 2026Core · 5761%
3.6 · 43% of topic15/25May/Jun 2026latest series · →A regular earner inside the topic — most papers touch it.Syllabus: why errors occur; parity check (odd/even, parity byte and block), checksum, echo check; check digits (ISBN, barcodes); automatic repeat query (ARQ)
- Next Paper 1
- 61%
- 6 in 10
- Marks a paper
- 3.6
- 5% of the paper · 43% of the topic
- Asked in
- 15 / 25
- Paper 1 sittings · 61 questions
- Last asked
- May/Jun 2026
- 0478/13 · Q2 · 3 marks · 4-series streak
- Asked in 15 of 25 Paper 1 sittings — about 6 papers in 10.
- About 3.6 marks a paper (5% of Paper 1; 43% of the topic's marks across its 3 bullets).
- Last asked May/Jun 2026 · 0478/13 · Q2 (3 marks) — in the most recent series.
- Asked in each of the last 4 series.
- Usually “Explain” or “Describe”: full sentences with a reason, not one-word answers.
- Biggest chunk of marks so far: 10 in May/Jun 2024 · 2210/11 · Q9.
- It is examined mostly as AO1 (Knowledge & understanding, 69%), the rest AO2 (21%) — definitions and descriptions in syllabus words score.
Last 12 sittings→ SteadyAssessment objectives
AO1 69%AO2 21%- AO1 Knowledge & understanding
- AO2 Apply to a context
- AO3 Evaluate & judge
- Explain57%
- Describe46%
- Identify39%
- Give31%
2.3Encryption#18 of 20 on Paper 1Occasional · 2937% next paper1.6 marks8/25 sittings↗ May/Jun 2026Occasional · 2937%
1.6 · 14% of topic8/25May/Jun 2026latest series · ↗Rotated in occasionally — the bullet students skip and then meet.Syllabus: the need for encryption when transmitting data; symmetric vs asymmetric encryption with public and private keys
- Next Paper 1
- 37%
- 1 in 4
- Marks a paper
- 1.6
- 2% of the paper · 14% of the topic
- Asked in
- 8 / 25
- Paper 1 sittings · 22 questions
- Last asked
- May/Jun 2026
- 0478/13 · Q2 · 4 marks
- Asked in 8 of 25 Paper 1 sittings — roughly one paper in 3.
- About 1.6 marks a paper (2% of Paper 1; 14% of the topic's marks across its 3 bullets).
- Last asked May/Jun 2026 · 0478/13 · Q2 (4 marks) — in the most recent series.
- Rising: 1.3 → 1.7 marks a paper.
- Usually “State” or “Describe”: short, precise answers in syllabus words.
- Biggest chunk of marks so far: 9 in May/Jun 2025 · 2210/11 · Q6.
- It is examined almost entirely as AO1 (Knowledge & understanding, 94%) — definitions and descriptions in syllabus words score.
Last 12 sittings↗ RisingAssessment objectives
AO1 94%- AO1 Knowledge & understanding
- AO2 Apply to a context
- AO3 Evaluate & judge
- State50%
- Describe46%
- Explain41%
- Give41%
23% of the topic's marks sit in question parts that belong to another topic (scenario questions cross sections) or that no bullet claims; they count for the topic, not for a bullet.
Marks a paper, year by year
Grey years are the previous syllabus (2015–2022, 76 questions) — history, not counted in the rates.
By exam series
- Feb/Mar4/4 · 23.8 mk
- May/Jun12/12 · 14.4 mk
- Oct/Nov9/9 · 11.7 mk
What you need to know3syllabus §2.1, §2.2, §2.3
- 2.1Types and methods of data transmission — packet structure (header, payload, trailer) and packet switching; serial vs parallel; simplex, half-duplex and full-duplex; the USB interface
- 2.2Methods of error detection — why errors occur; parity check (odd/even, parity byte and block), checksum, echo check; check digits (ISBN, barcodes); automatic repeat query (ARQ)
- 2.3Encryption — the need for encryption when transmitting data; symmetric vs asymmetric encryption with public and private keys
Video lectures20ZAK's YouTube channel · play here
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Infographics3draw these the way the examiner expects · download as PNG
Data packets & transmission modes
Error detection methods
Circuit vs packet switching
Key terms10use these exact words in the exam
Dotted terms are defined in the glossary.
Code help2referenced to the Cambridge pseudocode guide
DECLARE Byte : STRINGDECLARE i, Ones : INTEGERByte ← "10110010"Ones ← 0FOR i ← 1 TO 8IF SUBSTRING(Byte, i, 1) = "1" THENOnes ← Ones + 1ENDIFNEXT iIF Ones MOD 2 = 0 THENOUTPUT "Valid (even parity)"ELSEOUTPUT "Error detected"ENDIF
DECLARE Data : ARRAY[1:4] OF INTEGERDECLARE i, Sum : INTEGERData[1] ← 200Data[2] ← 150Data[3] ← 75Data[4] ← 33Sum ← 0FOR i ← 1 TO 4Sum ← Sum + Data[i]NEXT iOUTPUT "Checksum = ", Sum MOD 256
Playground examples6runnable programs for this topic
- Run
Check digit — ISBN-13
Weights 1 and 3 alternate, total MOD 10, subtract from 10. The classic check-digit algorithm.
- Run
Even parity check
Count the 1s in a byte; even parity means the count must be even.
- Run
Checksum of a block
Add the bytes and keep the remainder MOD 256; the receiver recalculates and compares.
- Run
Caesar cipher with ord() and chr()
Shift each letter by a key, wrapping round the alphabet with %. Non-letters are left alone.
- Run
ISBN-13 check digit
Weights 1 and 3 alternate; the check digit makes the total a multiple of 10.
- Run
Parity bit and checksum
Even parity on a 7-bit code, and a checksum as the sum of bytes mod 256.
Also for this topic: 3 Java programs · 3 VB.NET programs in the browser compilers.
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