If a network is computers talking to each other, two questions follow: what carries the signal (the transmission media), and how are the devices arranged (the topology)? This chapter answers both — and finishes by sizing networks from a personal Bluetooth link up to the worldwide Internet.
1Transmission media
Transmission media carry the data signal. They split into two families:
Guided media (wired — signal travels along a cable)
| Cable | Notes |
|---|---|
| Twisted pair | Pairs of copper wires twisted to reduce interference. Cheap, common (Ethernet/LAN cables). |
| Coaxial | A central copper core with shielding. Higher bandwidth than twisted pair (older cable TV/networks). |
| Fiber-optic | Carries data as light through glass. Fastest, longest range, immune to electrical interference — but costlier. |
Unguided media (wireless — signal travels through the air)
- Infrared — very short range, line-of-sight (old TV remotes).
- Radio waves — omnidirectional, medium range (Wi-Fi, FM radio).
- Microwaves — line-of-sight, long distance via towers.
- Satellite — very long distance, covers remote areas; higher delay.
Fiber-optic is the gold standard for speed and distance because it sends light, not electricity — so it's immune to electromagnetic interference and loses very little signal over long runs.
Key points
- Guided (wired): twisted pair (cheap, common), coaxial (more bandwidth), fiber-optic (fastest, uses light, immune to interference).
- Unguided (wireless): infrared (short, line-of-sight), radio (Wi-Fi), microwave (towers, line-of-sight), satellite (very long range).
- Fiber-optic is the fastest and longest-range guided medium.
2Network topologies
A topology is the arrangement — the layout — of devices in a network.
| Topology | Layout | Pros / Cons |
|---|---|---|
| Bus | All devices share one backbone cable | Cheap, simple / one cable fault can down the whole network |
| Star | All devices connect to a central hub/switch | Easy to manage, one device failing doesn't affect others / if the hub fails, all fail |
| Ring | Devices form a closed loop, data travels around it | Orderly data flow / a single break can disrupt the ring |
| Mesh | Every device links to every other | Very reliable (many paths) / expensive, lots of cabling |
| Tree | A hierarchy of star networks (branches) | Scalable / depends on the root/backbone |
Key points
- Topology = the physical/logical arrangement of devices.
- Bus = one shared backbone (cheap, single point of failure); Star = central hub (easy, but hub is critical).
- Ring = closed loop; Mesh = every device interconnected (reliable but costly); Tree = hierarchy of stars.
3Types of networks by size
Networks are classified by the area they cover, from smallest to largest:
| Type | Stands for | Range | Example |
|---|---|---|---|
| PAN | Personal Area Network | A few metres (around one person) | Bluetooth phone-to-earbuds |
| LAN | Local Area Network | A building or campus | A school's computer lab |
| MAN | Metropolitan Area Network | A city | A city-wide cable network |
| WAN | Wide Area Network | Countries / the world | The Internet |
Remember them by growing size: PAN → LAN → MAN → WAN (person → local → metro/city → wide/world). The Internet is the biggest WAN of all.
Key points
- By size: PAN (personal, ~metres), LAN (building/campus), MAN (city), WAN (countries/world).
- Bluetooth = PAN; a lab = LAN; a city network = MAN; the Internet = WAN.
- They grow in range: PAN → LAN → MAN → WAN.
★ Practical: design and classify
Answer briefly:
- Which topology would you choose for a computer lab, and why?
- Give one advantage of fiber-optic over twisted-pair cable.
- Classify each as PAN/LAN/MAN/WAN: Bluetooth earbuds, the Internet, a school lab, a city cable network.
- Why is a mesh topology very reliable but rarely used in homes?
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