| Medium | Type | Typical use | Advantages | Disadvantages |
|---|---|---|---|---|
| Twisted pair (UTP/STP) | Guided | LAN cabling (Cat5e, Cat6) | Cheap, easy | Limited to 100 m, interference |
| Coaxial cable | Guided | Cable TV, older LANs | Better shielding | Bulky |
| Optical fibre (single-mode, multi-mode) | Guided | Backbones, ISPs | Very high speed, long distance, immune to EMI | Costly, fragile to install |
| Radio waves / Wi-Fi | Unguided | WLAN, mobile | Mobility | Interference, security risk |
| Microwave / Satellite | Unguided | Long-haul, remote areas | Wide coverage | High latency, weather effects |
Guided media explained
Twisted pair cable contains four pairs of copper wires, with the two wires in each pair twisted around each other. The twisting matters: interference hits both wires of a pair almost equally, and the receiver only looks at the difference between them, so most of the noise cancels out. UTP (unshielded twisted pair) is the normal cable for office and home networks. STP (shielded twisted pair) adds foil shielding for places with a lot of electrical noise, such as factories. Cables come in categories: Cat5e supports 1 Gbps, Cat6 supports 1 Gbps (and 10 Gbps over shorter runs), and Cat6a supports 10 Gbps over the full 100 m.
Coaxial cable has one central copper conductor, surrounded by insulation, a braided metal shield and an outer jacket. The shield gives good protection from interference. It is still used for cable TV and cable Internet, but has been replaced by twisted pair in LANs.
Optical fibre carries pulses of light through a very thin strand of glass. The light stays inside the core by bouncing off the boundary with the surrounding glass (total internal reflection).
- Multi-mode fibre has a wider core and uses cheaper light sources. It is used for distances up to a few hundred metres, for example between buildings on a campus.
- Single-mode fibre has a very thin core and uses lasers. It reaches tens of kilometres, and is used by ISPs and undersea cables.
Because it carries light, not electricity, fibre is immune to electrical interference and lightning, is very hard to tap without being noticed, and has very low signal loss.
Unguided (wireless) media
Wireless signals spread through the air, so anyone in range can receive them. This gives mobility and avoids cabling costs, but it brings three issues: interference (from other networks, microwaves and Bluetooth), attenuation (walls and distance weaken the signal), and security (signals can be captured, so they must be encrypted).
- Radio waves (Wi-Fi, mobile networks, Bluetooth) pass through walls reasonably well.
- Microwave links need a clear line of sight between dishes, often on towers. They are used to join sites a few kilometres apart.
- Satellite links cover huge areas, including remote places. Traditional satellites orbit very high (about 36,000 km), which gives high latency (around 600 ms for a round trip). Newer low-orbit satellite services reduce this greatly.
- Infrared only works over a short, clear path, for example a TV remote.
Choosing a medium
Ask: How far must it go? How fast must it be? How much electrical noise is there? Is mobility needed? What is the budget? A typical school uses UTP from switches to PCs, fibre between buildings and between floors, and Wi-Fi for laptops and phones.
Remember
- Twisted pair: cheap and common, up to 100 m. Fibre: fastest, longest distance, immune to interference.
- Wireless gives mobility but suffers from interference and needs encryption.
- The choice depends on distance, speed, environment, mobility and cost.