Types and Methods of Data Transmission
Data Transmission · 4 question types
Exam Frequency Analysis
Past paper frequency (2018 to 2024)
This topic accounts for approximately 4% of your exam marks.
Serial vs parallel and simplex/half-duplex/full-duplex appear as definition or comparison questions.
Two completely different measures describe how "fast" a connection is. Exam questions often try to catch students mixing them up.
Bandwidth
Bandwidth is the maximum amount of data that can be transmitted per second across a connection, measured in bits per second (bps).
Bandwidth is a capacity: how wide the pipe is. A 100 Mbps connection can carry 100 million bits in every second. Higher bandwidth means more data per second.
Latency
Latency is the time delay between data being sent and being received, measured in milliseconds (ms).
Latency is a delay: how long it takes a single bit (or packet) to make the trip. A 30 ms ping means a packet takes 30 ms to travel from your computer to the server.
Why high bandwidth does not mean low latency
The two measures are independent. A satellite internet link can have:
- High (lots of data per second, because the satellite link is wide)
- High (each packet takes hundreds of milliseconds to travel up to the satellite and back down)
This is why satellite internet feels fine for downloading a film (high bandwidth lets the film stream in real time) but laggy for online gaming (high latency makes every button press feel delayed).
A fibre-to-home connection often has high bandwidth and low latency. A dial-up modem (if you could still find one) has low bandwidth and high latency. Different combinations exist for every kind of link.
Factors that affect transmission speed
When an exam question asks about "transmission speed", several things matter:
| Factor | Effect |
|---|---|
| Bandwidth of the link | A wider pipe carries more data per second |
| Distance / cable length | Longer cables introduce more signal loss; very long links may also have higher latency |
| Cable type | Fibre optic is much faster than copper twisted pair, which is faster than wireless radio |
| Interference and noise | Electromagnetic interference from nearby cables, motors, microwaves; physical obstacles for Wi-Fi |
| Number of users (contention) | A shared link slows down as more users compete for it |
| The quality of routers, switches and intermediate equipment | Old or overloaded routers add latency |
| Whether data is being compressed | Compressed data uses less bandwidth (covered in topic 3) |
Bandwidth, latency and packet switching
In packet switching:
- Bandwidth sets the maximum total amount of data the link can carry per second.
- Latency sets how long each individual packet takes to arrive.
- Network congestion affects both: contention reduces effective bandwidth and increases latency as packets sit in router queues.
For applications like video streaming, bandwidth is the headline number (you need enough capacity for the bitrate of the video). For online gaming or video calls, latency matters more, since even a fast link feels broken if every action arrives 500 ms late.