A network is two or more devices that can exchange data. That is the whole definition — everything else is a question of scale, shape and ownership. Two laptops sharing files over Wi-Fi is a network. So is the internet. The vocabulary in this topic exists so you can describe any given network precisely enough that somebody else could build it.
Classifying by geographic scale
| Type | Scale | Example | Typically owned by |
|---|---|---|---|
| PAN | A few metres | Bluetooth earbuds to a phone | One person |
| LAN | One building or site | A school's wired and wireless network | The organization |
| WLAN | One building, wireless | The Wi-Fi portion of that LAN | The organization |
| MAN | A city | A municipal fibre network | A city or carrier |
| WAN | Countries or worldwide | The internet; a company's inter-office links | Multiple carriers |
Client-server and peer-to-peer
- Dedicated servers provide resources; clients request them
- Central accounts, permissions and backups
- Scales to thousands of users
- Costs more; the server is a single point of failure
- Every device is both client and server
- No central administration — each machine manages its own sharing
- Cheap and quick for a handful of machines
- Becomes unmanageable past about ten devices; no central backup
A school or business runs client-server because it needs one place to create an account, set a permission and take a backup. Home networks are peer-to-peer, and file-sharing protocols like BitTorrent are peer-to-peer by design, because there is no central server to overload or shut down.
Topology: the shape of the wiring
| Topology | How it works | One cable breaks… | Used today? |
|---|---|---|---|
| Star | Every device has its own cable to a central switch | Only that one device drops off | Yes — the standard for wired LANs |
| Bus | All devices share one backbone cable | The whole segment goes down | Obsolete |
| Ring | Each device connects to the next, forming a loop | Breaks the ring unless it is dual-ring | Rare; survives in some fibre backbones |
| Mesh | Devices connect to several others | Traffic reroutes around the break | Yes — WAN backbones, Wi-Fi mesh |
Transmission media
- Twisted pair (UTP) — four twisted pairs of copper in a jacket. Cheap, easy to terminate, and limited to 100 m per run. The twisting is what cancels electromagnetic interference; untwisting more than about 13 mm at the connector degrades the cable.
- Coaxial — a central conductor inside a braided shield. Better interference rejection, now mostly used for cable internet and antenna feeds.
- Fibre optic — light through glass. Immune to electromagnetic interference, runs kilometres, offers enormous bandwidth, but costs more and needs specialized termination.
- Wireless (Wi-Fi) — radio in the 2.4 GHz, 5 GHz and 6 GHz bands. Convenient, but shared, interference-prone and easier to intercept.
| Cable category | Speed | Distance |
|---|---|---|
| Cat 5e | 1 Gb/s | 100 m |
| Cat 6 | 1 Gb/s (10 Gb/s to 55 m) | 100 m |
| Cat 6a | 10 Gb/s | 100 m |
| Multi-mode fibre | 10–100 Gb/s | Up to ~550 m |
| Single-mode fibre | 10–400 Gb/s | Tens of kilometres |
Wireless has its own trade-offs. The 2.4 GHz band travels further and penetrates walls better but has only three non-overlapping channels and is crowded with microwaves and Bluetooth. The 5 GHz band has far more channels and less interference but shorter range. Every wireless client on an access point shares the same airtime, so thirty devices on one AP each get a fraction of its throughput — unlike a switch, where every port gets its own full bandwidth.