Exam Frequency Analysis
Past paper frequency (2018 to 2024)
This topic accounts for approximately 4% of your exam marks.
stable
Rare
Stable4%
Serial vs parallel and simplex/half-duplex/full-duplex appear as definition or comparison questions.
When a large piece of data travels across a network, it is rarely sent in one go. Instead, the Transmission Control Protocol (TCP) chops the data into small packets that travel across the network independently and are reassembled at the far end.
Small packets are easier to route, because each one can take the quickest available path through the network rather than waiting for one huge chunk to find an uncongested route.
Inside a packet
Every packet contains three sections:
| Section | What it holds |
|---|---|
| Header | The source IP address (which device sent it), the destination IP address (where it is going), and the packet number (e.g. "packet 3 of 5") so the pieces can be put back in order |
| Payload | The actual data being transported (part of an email, part of a web page, part of a video, etc.) |
| Trailer | An end-of-packet marker and an error-check value (a checksum or parity bit) so the receiver can detect corruption |
If a packet is corrupted in transit, the receiver can ask the sender to resend just that one packet rather than the whole message.
