GCSE Computer Science: Networks and the Internet

Networking answers go wrong in two ways at GCSE: a term is defined by the wrong property, or a measurement is read in the wrong units. Both are built into the wrong options here.

A firm has computers in one building and a link between two cities, and the answer has to turn on geographic scope and who owns the cable in between — not on how many machines there are, which is the definition students most often reach for. A school with central accounts and managed backups is set against a club sharing files laptop to laptop, and the answer names what the second arrangement gives up rather than simply labelling both.

The star topology is given through its behaviour: one cable fails and one machine goes quiet, the central switch fails and everything stops. Those two facts together are the point, and "a star has no single point of failure" is standing there for anyone who has learned only half of it. Packets get the same treatment — the reason is routing around congestion and resending only the part that was lost, not that packets are somehow faster.

Two questions are about addresses and names. A laptop moves from a home network to a coffee shop, keeps one address and is given another, which is the whole of the MAC-against-IP distinction stated as something that happens. And typing a name into a browser leads to a numbered address, because the network routes on numbers and the lookup is what supplies them.

Then the measurements. A file of sixty megabits over a connection of twenty megabits a second takes three seconds, and among the wrong answers is twenty-four — which is the correct answer to a different question, the one where the file is read as megabytes. That is the most common way this mark is lost, so the explanation derives it rather than just warning about it. Bandwidth and latency are separated by a connection that carries a great deal and still lags on a live call.

The set closes on a secure address, where the answer has to do two things at once: say that the traffic between browser and site is encrypted so an interceptor cannot read it, and say that this is not a statement about whether the site is honest or its content accurate.

Everything here is defensive. No attack, interception method or technique is described anywhere. Every firm and school is invented, and no real company, product or website is named. Nothing is reproduced from any exam board specification, past paper or mark scheme.

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• Tell a LAN from a WAN by scope and infrastructure rather than by size
• Say what client-server offers and what peer-to-peer gives up
• State both halves of the star topology's failure behaviour
• Explain why data is sent in packets
• Distinguish a MAC address from an IP address and say what each is for
• Say what a domain name lookup does and why it is needed
• Choose wired or wireless against a stated requirement
• Calculate a transfer time, checking the units before dividing
• Separate bandwidth from latency
• State what a secure protocol protects and what it does not vouch for

Ten invented networks and situations: an office and a two-city link, a school server and a club sharing files, one cable down and then the switch, data sent in pieces, a laptop in a coffee shop, a name typed into a browser, a warehouse full of moving devices, sixty megabits over a twenty megabit connection, a fast line with a stuttering video call, and an address beginning with a secure protocol. Twelve flashcards carry the vocabulary — LAN, WAN, client-server, peer-to-peer, star and mesh topology, packet, protocol, MAC address, IP address, bandwidth, latency.