Data communication and transmission media
Data communication moves data from a sender to a receiver over a medium, which may be wired (guided) or wireless (unguided).
The data communication model
A protocol, an agreed set of rules such as TCP/IP, controls every step so both ends understand each other.
Guided (wired) media
| Medium | How it carries data | Typical use | Points to note |
|---|---|---|---|
| Twisted pair cable | Electrical signals on twisted copper wire pairs | Telephone lines, office LANs (Ethernet) | Cheap and easy to fit; limited distance; affected by interference |
| Coaxial cable | Electrical signals on a copper core inside a metal shield | Cable TV, older networks | Better shielded than twisted pair; thicker and costlier |
| Fibre optic cable | Pulses of light inside thin glass fibres | Backbone links, fibre-to-the-home broadband, undersea cables | Very fast, long distance, no electrical interference; costly to lay |
Unguided (wireless) media
| Medium | Typical use | Points to note |
|---|---|---|
| Radio waves | Wi-Fi, Bluetooth, mobile networks (4G, 5G) | Easy, mobile access; can be overheard, so needs encryption |
| Microwave | Links between towers in line of sight | Fast over long distances; blocked by hills and buildings |
| Satellite | Satellite TV, remote areas, ships | Covers a huge area; signal delay; costly |
| Infrared | TV remotes, some short-range links | Very short range; needs a clear line of sight |
Transmission modes
| Mode | Direction | Example |
|---|---|---|
| Simplex | One way only | Radio or TV broadcast |
| Half duplex | Both ways, but one at a time | Walkie-talkie |
| Full duplex | Both ways at the same time | Telephone call |
How long will a file take to send?
A firm's broadband line runs at 100 Mbps. How long does a 50 MB file take to send, ignoring overheads? (1 byte = 8 bits, so take 1 MB = 8 megabits.)
- Change the file size to bits: 50 MB × 8 = 400 megabits
- Time = size ÷ speed = 400 megabits ÷ 100 megabits per second
- = 4 seconds
About 4 seconds; in practice a little longer because of overheads. Note: Mbps means megabits per second, while MB means megabytes.
In Sri Lanka, SLT-Mobitel sells fibre (FTTH) broadband to homes and offices, Dialog and other operators sell 4G wireless broadband over radio waves, and international internet traffic reaches the island through undersea fibre-optic cables.
Short answer: “What is a protocol?” An agreed set of rules for sending and receiving data, so that different devices understand each other, e.g. TCP/IP.
Structured question: “Compare twisted pair, coaxial and fibre optic cable.” Compare how each carries data, speed, distance, interference, cost and typical use. A table works well.
Essay: “Explain data communication and the transmission media used in computer networks.” Draw the communication model, explain its elements and protocol, then guided and unguided media, and factors for choosing a medium.
Guided = T-C-F (Twisted pair, Coaxial, Fibre). Unguided = R-M-S-I (Radio, Microwave, Satellite, Infrared). Mbps = megabits, not megabytes.