Data Transmission

What this lesson covers

Data Transmission is a 7-part O Level Computer Science lesson. Each part makes one point and then hands over to the next, so it can be read in a sitting or picked up again at the part you stopped on. It defines the idea in plain words before using it, works through an example step by step, breaks the topic into its parts and compares them, shows where it is used outside the textbook, names the mistakes that cost marks in an exam, ends with a recap of what to remember.

How it begins

Data is split into packets. Each has a header (sender and receiver addresses, packet number, how many packets in total), a payload (the data itself, typically about 64 KiB) and a trailer (an error-checking value and a marker for the end). In packet switching, routers send each packet by whichever route is least congested, so packets may arrive out of order, or not at all.

The 7 parts

1. Packets and packet switching
2. Serial, parallel and the three directions
3. Error detection: what each method catches
4. Encryption
5. Where marks go
6. What to remember
7. Watch one worked through