Comparing Media
Knowing what metal wire, optic fibre, radio and satellite links each do is only half the job — the real skill examiners look for is choosing the right one for a specific situation. This lesson compares the media from the previous lesson against three criteria — data rate, cost, and security — and turns that comparison into a genuine decision-making tool.
Three criteria for comparing transmission media
No transmission medium is simply "the best" — every choice is a trade-off between how much information it can carry, how much it costs to use, and how secure it is against interception. Comparing metal wire, optic fibre, radio/microwave and satellite links against these three criteria is the basis of almost every extended-response question on this part of the specification.
- Data transmission rate. How much information the medium can carry per second — its bandwidth or capacity. Optic fibre generally offers the highest data rates of any medium discussed here, since light has an extremely high frequency and can be modulated extremely fast. Metal wire and radio/microwave links generally offer lower, more limited capacity, though the exact figures depend heavily on the specific technology and frequencies in use.
- Cost. The expense of installing and running the link. Metal wire and free-space radio/microwave links are often relatively cheap to set up over short distances, or where suitable infrastructure already exists. Laying optic fibre cable — especially over long distances or difficult terrain — tends to involve a larger upfront installation cost, though it can become more cost-effective than the alternatives for very high-capacity, long-distance links, since a single fibre can replace many lower-capacity wire or radio links. Satellite systems involve a very large initial cost (building and launching the satellite itself), but can be economical for covering remote or widely-dispersed areas that would otherwise need enormous amounts of ground infrastructure.
- Security. How easily a third party could intercept the signal without authorisation. Any signal travelling through free space — radio, microwave, satellite links — can in principle be picked up by anyone with a suitable receiver within range, making these media inherently less secure unless the signal is separately encrypted. A signal confined within a physical cable, whether wire or fibre, is comparatively much harder to intercept, since doing so generally requires direct physical access to the cable itself. Optic fibre has a further security advantage: unlike current-carrying wire, it does not leak electromagnetic radiation that could be detected and decoded from outside the cable.
| Medium | Typical data rate | Typical cost | Typical security |
|---|---|---|---|
| Metal wire | Low–moderate | Low (short/existing runs) | Moderate (needs physical access) |
| Optic fibre | Very high | High upfront, efficient long-term | High (no leaked radiation) |
| Radio / microwave | Moderate | Low–moderate (no cable needed) | Low (interceptable in free space) |
| Satellite | High | Very high upfront, efficient for remote areas | Low (interceptable in free space) |
Matching medium to application
The genuine skill being tested isn't reciting these properties in the abstract — it's applying them to a specific scenario and justifying a choice. A few representative examples:
- Connecting two buildings on the same site. A wire or a short fibre run is usually the sensible choice: the distance is short, so cost stays low, and a physical cable is both convenient and comparatively secure against casual interception.
- A rural community far from existing infrastructure. Satellite or long-range radio avoids the enormous expense of laying cable across difficult, sparsely-populated terrain, even though the ongoing running cost or security is worse than a cabled link would offer.
- A high-capacity international data backbone. Optic fibre is standard here: the very high data rate needed to carry enormous volumes of traffic between countries easily justifies the large upfront infrastructure cost.
- A mobile or moving device, such as a phone. Radio is really the only option, since it's the only medium here that doesn't require a fixed physical cable connecting transmitter to receiver at all times.
Every exam question of this type is really asking you to weigh the same three factors — data rate, cost, and security — against the specific demands of a specific application. A medium that's clearly correct for a high-capacity fixed link (optic fibre) can be clearly wrong for a mobile device (which needs radio) or a remote community (where satellite avoids infeasible cabling costs). Always answer "best for what, and why," never "best" on its own.
Key takeaways
- Data transmission rate, cost, and security are the three criteria used to compare transmission media.
- Optic fibre generally offers the highest data rate; metal wire and radio/microwave are generally lower and more limited.
- Wire and radio/microwave links are often cheaper for short distances or existing infrastructure; fibre has higher upfront cost but suits high-capacity long-distance links; satellites have very high upfront cost but suit remote areas.
- Free-space signals (radio, microwave, satellite) are inherently easier to intercept than signals confined to a physical cable (wire or fibre).
- Optic fibre has an added security advantage: it doesn't leak detectable electromagnetic radiation the way current-carrying wire can.
- Matching medium to application means weighing required data rate, acceptable cost, and necessary security against the specific situation, not picking a single universally "best" medium.
- Short fixed links favour wire/fibre, remote areas favour satellite or long-range radio, high-capacity backbones favour fibre, and mobile devices require radio.