IGCSE Computer Science Paper 1 Definitions Worksheet: 2.1 Data Transmission Types and Methods (Modules 110–120)
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Key terms
Write what each term means, in your own words.
1
header, payload, trailer
2
packet header
3
destination address
4
originator's address
5
packet number
6
payload
7
packet trailer
8
packet switching
9
routing
Answer Key
IGCSE Computer Science Paper 1 · Modules 110–120 · Student wording will vary for definitions
1header, payload, trailer — The three parts of a packet, in order: the header (start) holds addresses and packet number, the payload (middle) holds the data, the trailer (end) marks the packet's end.
2packet header — The first part of a packet. It holds control information: the destination address, the originator's address and the packet number, used to deliver and reassemble the packet.
3destination address — The address in a packet header of the device the packet must be delivered to. Routers read it to choose where to send the packet. It is usually an IP address.
4originator's address — The IP address of the device that sent the packet, held in the header so the receiver knows who sent it and can reply or ask for a resend. It differs from the destination address.
5packet number — A number in the packet header showing the packet's position in the whole message (e.g. packet 3 of 10), so packets that arrive out of order can be put back in the right order.
6payload — The part of a packet that carries the actual data being sent, such as a piece of a file or message. The header and trailer are not payload.
7packet trailer — The last part of a packet. It marks where the packet ends and can hold error checking information, so the receiving device can check the data arrived correctly.
8packet switching — Data is split into packets that are sent separately, each routed on its own from router to router, then joined back together in the right order at the destination.
9routing — A router reads each packet's destination address in its header and picks the next router to send it to, so every packet's route is decided one step at a time.