Information Technology · Ch 1 — Networking and Open Standards
Communication Media
Communication Media
Communication media (also called transmission media) are the paths along which data signals travel from one device to another in a network. They fall into two broad groups — wired (guided) media, where the signal travels through a physical cable, and wireless (unguided) media, where the signal travels through the air as waves.
A. Wired (guided) media.
1. Twisted-pair cable. This is made of pairs of copper wires twisted together (the twisting reduces interference). It is the most common and cheapest cable, used in telephone lines and most LANs. It comes in unshielded (UTP) and shielded (STP) forms. It is easy to install and low-cost, but carries signals a shorter distance and at lower speed than fibre.
2. Coaxial cable. This has a central copper conductor surrounded by insulation, a metal shield, and an outer cover. It carries signals over longer distances and at higher speeds than twisted pair and resists interference better; it was widely used for cable television and older networks.
3. Optical-fibre cable. This carries data as pulses of light through very thin strands of glass or plastic. It offers very high speed, very large capacity (bandwidth), and long distance, and is immune to electrical interference and very secure. Its drawbacks are higher cost and more difficult installation and repair. Fibre is used for high-speed Internet backbones and long-distance links.
| Wired medium | Signal carried by | Speed / distance | Cost |
|---|---|---|---|
| Twisted pair | Electricity in copper | Lower / shorter | Low |
| Coaxial cable | Electricity in copper (shielded) | Medium / medium | Medium |
| Optical fibre | Light in glass/plastic | Very high / very long | High |
B. Wireless (unguided) media. Here signals travel through the air, with no cable, which is convenient where cabling is difficult and allows mobility.
1. Radio waves. These travel in all directions and can pass through walls, so they suit communication over medium distances without a clear line of sight — used in Wi-Fi, cordless phones, and radio broadcasting.
2. Microwaves. These are high-frequency waves that travel in a straight line between two dish antennas that must be in line of sight (for example, on tall towers). They carry large amounts of data over long distances and are used for long-distance telephone and data links.
3. Infrared. These are short-range waves that need a clear, direct line of sight and cannot pass through walls — used for very short-distance links such as a TV remote control. …