IGCSE Computer Science (0478) · Paper 1 — Computer Systems
Data Transmission
Packet structure, transmission methods, USB and error-detection questions reward precise terminology — "checksum" and "parity check" are marked as distinct answers, not synonyms.
2.1 Types and methods of data transmission
- Understand that data is broken down into packets to be transmitted.
- Describe the structure of a packet, including the packet header (destination address, packet number, originator's address), payload and trailer.
- Describe the process of packet switching, including the role of a router and reordering of out-of-order packets.
- Describe how data is transmitted from one device to another using different methods of data transmission: serial, parallel, simplex, half-duplex, full-duplex.
- Explain the suitability of each method of data transmission for a given scenario, including advantages and disadvantages.
- Understand the universal serial bus (USB) interface and explain how it is used to transmit data, including its benefits and drawbacks.
2.2 Methods of error detection
- Understand the need to check for errors after data transmission and how these errors can occur (e.g. interference causing data loss, gain or change).
- Describe the processes involved in parity check (odd and even, including parity byte and parity block check), checksum and echo check for detecting errors after transmission.
- Describe how a check digit is used to detect errors in data entry and identify examples of when a check digit is used, including ISBN and bar codes.
- Describe how an automatic repeat query (ARQ) can be used to establish that data is received without error, including positive/negative acknowledgements and timeout.
2.3 Encryption
- Understand the need for and purpose of encryption when transmitting data.
- Understand how data is encrypted using symmetric and asymmetric encryption, including the use of public and private keys.
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