CIE IGCSE | TOPIC 2 ASSESSMENT
DATA TRANSMISSION: END OF TOPIC REVIEW
Check your understanding of packets, transmission methods, USB, error detection and encryption. Work independently before checking your answers.
BEFORE YOU BEGIN
Suggested time: 20–30 minutes. Complete sections A and B without notes. Write section C answers in your exercise book before revealing the marking guidance.
Sections A and B provide an automatic score out of 11, one point for each fully correct item. Section C has 10 suggested written marks, assessed separately. These are original practice questions, not an official Cambridge paper or grade boundary.
For calculations, show working in your book and enter the answer in the unit requested. Calculator use can follow your teacher’s instructions. Your answers remain only while this page is open.
C | EXAM-STYLE WRITING
Write in your exercise book before revealing the guidance. Section C assesses subject knowledge and gives you practice expressing it clearly. The first table reproduces the command-word meanings supplied from the Cambridge syllabus. The second gives practical writing guidance for this review.
| CIE command word | Meaning from the specification |
|---|---|
| Calculate | work out from given facts, figures or information |
| Compare | identify/comment on similarities and/or differences |
| Define | give precise meaning |
| Demonstrate | show how or give an example |
| Describe | state the points of a topic / give characteristics and main features |
| Evaluate | judge or calculate the quality, importance, amount, or value of something |
| Explain | set out purposes or reasons / make the relationships between things clear / say why and/or how and support with relevant evidence |
| Give | produce an answer from a given source or recall/memory |
| Identify | name/select/recognise |
| Outline | set out the main points |
| Show (that) | provide structured evidence that leads to a given result |
| State | express in clear terms |
| Suggest | apply knowledge and understanding to situations where there are a range of valid responses in order to make proposals / put forward considerations |
The command applies to the subject context. A brief identification does not need an essay; an explanation needs accurate links. Use the guidance below for the four commands in this written review.
| Command word | What your answer should do | Useful writing pattern |
|---|---|---|
| Describe | State the main features or relevant points; for a process, make the sequence clear. | First… Next… Finally… |
| Explain | Give reasons, purposes or clear relationships, supported by relevant subject knowledge. | …because…; therefore…; resulting in…; leading to… |
| Compare | Identify similarities and/or differences, addressing both things on the same basis. | Both…; whereas…; unlike… |
| Evaluate | Make a reasoned judgement about suitability or value in the given context. | A benefit is…; however…; therefore, for this purpose… |
BUILD A CLEAR EXPLANATION
Point → reason or mechanism → consequence. Connectives help show the relationship, but the technical link must be accurate. Adding “because” to an unsupported claim does not make it a good explanation.
Thin answer: “The sender sends it again.”
Developed answer: “Because the sender receives no expected acknowledgement, its timer reaches the timeout, therefore it retransmits the data.”
Use because or because of to introduce a cause; therefore, resulting in or leading to to show a consequence. For comparison, use both and whereas. For evaluation, use however and finish with a justified judgement.
Write enough relevant detail for the marks available. Clear, concise sentences are better than padding. These are writing supports, not compulsory phrases or separate official language marks.
12 | PACKET SWITCHING
[3 suggested marks]
Describe how packet switching transmits a message and reconstructs it at the destination.
Sample answer: First, the sender divides the message into packets with control information. Routers forward each packet towards its destination, and packets may follow different routes. Once all required packets arrive, the receiver uses packet numbers to reorder them and joins their payloads to reconstruct the message.
- Data divided into packets with control information: one mark.
- Routers forward packets; different routes are possible: one mark.
- Receiver reorders using packet numbers and reassembles: one mark.
Writing focus: describe the sequence accurately. Do not say every packet must take a different route or that a router reconstructs the message.
13 | LOST ACKNOWLEDGEMENT
[3 suggested marks]
A packet passes the receiver’s error check, but its acknowledgement is lost. Explain why the sender may transmit the packet again and how duplicate delivery can be avoided.
Sample answer: Because the sender receives no expected acknowledgement, it cannot confirm acceptance. Its timer therefore reaches the timeout and triggers retransmission. The receiver can use the packet’s sequence identifier to recognise the repeat, avoiding duplicate delivery while sending an acknowledgement again.
- Missing acknowledgement means acceptance is not confirmed to the sender: one mark.
- Timeout linked to retransmission: one mark.
- Sequence identification linked to recognising duplicates / avoiding duplicate delivery: one mark.
Writing focus: connect the missing response, timeout and consequence. Do not claim timeout proves the original packet was corrupted.
14 | ENCRYPTION KEYS
[2 suggested marks]
Compare symmetric and asymmetric encryption in terms of the keys used for encryption and decryption, and which keys must remain secret.
Sample answer: Symmetric encryption uses the same shared secret key for encryption and decryption, whereas asymmetric encryption uses a related public/private pair. For confidential delivery, the receiver’s public key encrypts and their private key decrypts. The symmetric shared key must remain secret, while the asymmetric public key can be shared and the private key must remain secret.
- Linked comparison of the shared-key approach and public/private roles: one mark.
- Linked comparison of which keys are secret: one mark.
Writing focus: address both methods on the same points, using “whereas” or “while” where useful. Do not reverse the public/private roles.
15 | USB IN A CLASSROOM
[2 suggested marks]
A teacher wants four students to copy large video files simultaneously to external drives through one USB hub. Evaluate this arrangement, considering convenience and transfer performance. Give a justified judgement.
Sample answer: A hub conveniently adds connections so several drives can be attached. However, they share its upstream connection, so simultaneous transfers may compete for bandwidth and take longer. Therefore the arrangement may suit occasional copying when time is flexible, but separate suitable host connections or staggered transfers may be preferable if fast completion is important. Actual performance also depends on the drives, cables and ports.
- A relevant convenience benefit weighed against shared-bandwidth limits: one mark.
- A contextual judgement justified by the trade-off: one mark.
Writing focus: weigh both factors and conclude for the stated purpose. Do not claim a hub guarantees four times the speed or that separate ports always have independent controllers.
CHECK YOUR WRITTEN COMMUNICATION
- Did I answer the command word, rather than just name facts?
- For explain, did I show an accurate reason or cause-and-effect link?
- For compare, did I address both things on the same point?
- For evaluate, did I weigh relevant factors and justify my judgement?
- Did I use precise terms and connectives naturally, without repeating or padding?
Self-assess using the suggested content marks, keeping the written total separate from your automatic score. Use the writing checklist to improve an answer rather than adding unofficial language marks.
YOUR NEXT REVISION STEP
Submit sections A and B to see suggested lessons to revisit.
For written work, revisit packets, error detection and ARQ, encryption and USB where needed.
This review samples the topic; it is not a complete syllabus assessment. Also check simplex/full-duplex, parity blocks, echo checks and checksum limitations using the full Topic 2 revision page.
Choose two weak areas, revisit their explanations and attempt a fresh example. Repeating the same questions after feedback shows learning, rather than an independent assessment.