IGCSE Computer Science: Data Transmission (Cambridge 0478)

This guide covers Topic 2 Data transmission, for Cambridge IGCSE Computer Science 0478, 2026–2028 series (Version 5, published December 2025). 0478 is not tiered, and this is the plain A*-G qualification, distinct from the numeric-grade Cambridge IGCSE (9-1) Computer Science 0984 sibling syllabus.

Where this fits in 0478

Data transmission is the second of six topics grouped under “Computer systems,” sitting between Data representation and Hardware. Where Topic 1 established that everything a computer handles is ultimately binary, Topic 2 asks what happens to that binary data once it needs to move from one device to another — how it is packaged, what can go wrong in transit, how errors are caught, and how the data is kept private along the way. The packet structure and network concepts introduced here are picked up again later in Topic 3.4 (Network hardware) and Topic 5 (The internet and its uses), which both assume candidates already understand how data physically moves across a network before discussing the hardware and protocols built on top of that movement.

Syllabus coverage

CAMBRIDGE IGCSE COMPUTER SCIENCE 0478 — TOPIC 2 DATA TRANSMISSION

• 2.1 Types and methods of data transmission — understanding that data is broken down into packets for transmission and describing a packet’s structure (a packet header containing the destination address, packet number and originator’s address, a payload, and a trailer); describing the process of packet switching, including that a router controls the route each packet takes, that different packets from the same transmission may travel by different routes, that packets can arrive out of order, and that they are reordered once the last one arrives; describing how data is transmitted using serial, parallel, simplex, half-duplex and full-duplex methods and explaining which is suitable for a given scenario, including the advantages and disadvantages of each; understanding the universal serial bus (USB) interface and explaining how it is used to transmit data, including its benefits and drawbacks.
• 2.2 Methods of error detection — understanding the need to check for errors after data transmission and how transmission errors occur (for example through interference causing data loss, data gain or data change); describing the parity check (odd and even, including parity byte and parity block check), the checksum, and the echo check as methods of detecting errors in transmitted data; describing how a check digit is used to detect data-entry errors, with examples including international standard book numbers (ISBN) and bar codes; describing how an automatic repeat query (ARQ) — using positive and negative acknowledgements plus a timeout — is used to confirm that data has been received without error.
• 2.3 Encryption — understanding the need for, and purpose of, encryption when transmitting data; understanding how data is encrypted using symmetric and asymmetric encryption, including that asymmetric encryption uses a public key and a private key.

How to approach it

Packet switching is the concept most often tested with a “describe the process” style question, so practise narrating it as a sequence rather than a list of facts: a message is broken into packets, each packet is given a header containing the destination address, an originator’s address and a packet number, packets can travel independently by different routes as directed by routers along the way, they may therefore arrive out of order, and the receiving device uses the packet numbers to reassemble them correctly once the final packet arrives. For the transmission methods in 2.1, the exam typically gives a scenario — a printer cable, a long-distance network link, a keyboard — and asks which method suits it and why; build a short mental table of serial vs parallel (distance and cost vs speed over short runs) and simplex vs half-duplex vs full-duplex (one-way only, alternating two-way, or simultaneous two-way) so you can match a scenario to a method quickly rather than re-deriving the trade-offs from scratch under time pressure. The three error-detection methods in 2.2 are frequently confused with each other because they all serve the same general purpose; keep them distinct by what each one actually checks — a parity check counts the number of 1-bits and compares it against an expected odd or even total, a checksum is a calculated value sent alongside the data and recalculated on arrival for comparison, and an echo check simply sends the received data back to the sender to be compared with the original. Check digits are a related but separate idea worth not conflating with the other three: they validate a single piece of entered data, such as an ISBN or barcode number, rather than an entire transmitted packet. For encryption in 2.3, the exam distinction that matters most is that symmetric encryption uses one shared key for both encrypting and decrypting, while asymmetric encryption uses a mathematically linked public/private key pair — data encrypted with the public key can only be decrypted with the matching private key — and being able to state that difference precisely, rather than just naming both terms, is usually where the marks sit.

It also pays to connect 2.1 and 2.2 explicitly rather than revising them as two unrelated sections: packets are switched and routed independently precisely because a network cannot guarantee a clean, uninterrupted path from sender to receiver, and that same unreliability is exactly why error detection in 2.2 exists at all. A well-prepared answer to a “why do we need error detection” question draws on this link — interference, congestion and equipment faults during the packet-switched journey described in 2.1 are the reasons data can arrive corrupted, which is what the parity check, checksum, echo check and ARQ in 2.2 exist to catch and, where possible, correct. When revising the USB interface specifically, resist the temptation to treat it as a footnote: past questions have asked candidates to explain both a benefit (a standardised, widely supported connector that also supplies power) and a drawback (transmission speed limits compared with some dedicated interfaces, and a maximum practical cable length), so prepare at least one of each rather than assuming the topic is too minor to be examined in its own right.

Official syllabus

Cambridge IGCSE Computer Science 0478 syllabus for 2026, 2027 and 2028 (Version 5, December 2025) — cambridgeinternational.org.