Theory
What the data physically travels through
Beneath all the abstraction, network data has to travel through something physical, a cable (or radio waves for Wi-Fi). The kind of cable sets real limits: how fast data can go, how far it can travel, how much it costs, and how well it resists interference.
Three cable types matter for this course: coaxial, UTP (twisted pair), and fiber optic. The big divide is between the copper cables, which carry electrical signals, and fiber, which carries light. This lesson compares them.
At a glance
| Cable | Carries | Character |
|---|---|---|
| Coaxial | Electrical signal on a shielded copper core | Moderate speed and distance; older; used in early networks and cable TV |
| UTP (twisted pair) | Electrical signal on twisted copper pairs | Cheap, flexible, the common LAN cable (Cat5e/Cat6, RJ45); about 100 m limit |
| Fiber optic | Pulses of light through glass fibres | Fastest, longest range, immune to interference; costlier and less flexible |
Theory
Copper vs light
Coaxial and UTP are both copper: they carry an electrical signal. Coaxial wraps a copper core in a metal shield that guards against interference, and was common in older networks. UTP twists pairs of wires together (the twisting itself cancels out much interference), and is cheap, flexible, and everywhere in modern LANs, the cable with the familiar RJ45 clip that plugs into your computer, good for runs up to about 100 metres.
Fiber optic is different in kind: it sends data as pulses of light down a thin strand of glass. Light carries far more data, over far greater distances, and does not care about electrical interference, though fiber costs more and is more delicate to handle.
Formula
UTP for the desk, fiber for the backbone
In practice, the choice is about matching cost to need. UTP is the everyday workhorse: cheap and flexible, it wires up offices and labs, connecting each computer to the switch over short distances.
Fiber optic is reserved for where its strengths pay off: backbones and long-haul links carrying huge amounts of traffic between buildings, cities, and continents, where its speed, distance, and immunity to interference justify the higher cost. So a student's laptop likely connects by UTP, but the data then races across fiber for the long journey.
Quiz
Which cable transmits data as pulses of light and offers the highest speed over the longest distances, immune to electromagnetic interference?
- UTP, because twisted pairs carry light
- Fiber optic, which sends light through glass fibres for the highest bandwidth and range
- Coaxial, because its shield carries light
- None; all cables are equally fast
Show the answer
Fiber optic, which sends light through glass fibres for the highest bandwidth and range
Fiber optic transmits data as pulses of LIGHT through thin glass (or plastic) fibres, giving the highest bandwidth, the longest reach, and immunity to electromagnetic interference (light is not affected by electrical noise). Option A is wrong: UTP is twisted-pair COPPER carrying an electrical signal, not light. Option C is wrong: coaxial is also copper (a shielded electrical conductor); its metal shield reduces interference but does not carry light. Option D is false: cable types differ substantially in speed and distance, fiber clearly outperforms copper for bandwidth and range. The defining fact: fiber carries light (fast, far, interference-immune), while coaxial and UTP carry electrical signals over copper.
Think first
Why is fiber immune to electromagnetic interference when copper is not?
Copper cables can pick up electrical noise, but fiber does not. What makes the difference? Then tap.
Show the answer
Because copper carries information as an ELECTRICAL signal, which nearby electromagnetic fields can disturb, while fiber carries it as LIGHT, which those fields cannot touch. In a copper cable, data is a changing electric current, and any nearby source of electromagnetic energy, a motor, a power line, another cable, fluorescent lights, can induce stray currents that corrupt the signal (this is why UTP twists its pairs and coaxial adds a shield: both are attempts to fight off electrical interference). Fiber optic works on a completely different principle: the data is encoded as pulses of light travelling inside a glass fibre, and light is an electromagnetic wave at frequencies that external electrical noise simply does not couple into. No electric current flows in the fibre to be disturbed, so motors, power lines, and radio noise have essentially no effect. This immunity is a major reason fiber is chosen for long-haul and high-reliability links, and for running cable through electrically noisy environments where copper would suffer. It also means fiber does not radiate signal that others could tap as easily, a security bonus. So the interference immunity is not a minor tweak; it is a direct consequence of using light in glass instead of electricity in metal. Different medium, different physics, no electrical noise to catch.
Summary
Key takeaways
- Cables are the physical medium data travels through, setting limits on speed, distance, cost, and interference resistance.
- Coaxial: an electrical signal on a shielded copper core; moderate speed and distance; older technology.
- UTP (twisted pair): cheap, flexible copper, the common LAN cable (Cat5e/Cat6, RJ45), good to about 100 m.
- Fiber optic: pulses of light through glass; highest speed and longest distance, immune to electromagnetic interference; costlier.
- Copper (coaxial, UTP) carries electrical signals; fiber carries light.
- In practice: UTP wires desks to switches; fiber carries backbones and long-haul traffic.
- Memory hook: UTP copper for the desk, fiber light for the long haul.