Skip to main content

Physical description of guided media

Short answer

Twisted pair consists of two insulated copper wires twisted together, bundled in a sheath; UTP has no shield, STP has a metal shield. Coaxial cable has a central conductor, insulating dielectric, braided shield, and outer jacket. Optical fibre has a glass or plastic core, cladding with lower refractive index, and a protective jacket.

Briefly describe the physical description of each guided transmission medium.

Guided media are physical cables that direct the signal along a fixed path. The three common types are:

1. Twisted pair cable

Two insulated copper wires (typically 22-26 AWG, a conductor about 0.4 to 0.65 mm in diameter) twisted together in a regular spiral. Many pairs are bundled in one sheath. There are two types:

  • UTP: no shield, only a plastic jacket (Cat 3, 5e, 6).
  • STP: pairs covered by a metal foil or braid.

The twisting cancels interference and crosstalk.

2. Coaxial cable

 [ outer plastic jacket ]
   [ braided metal shield (outer conductor) ]
     [ insulating dielectric ]
       ( inner copper conductor )

A central solid or stranded copper conductor, surrounded by an insulator, then a braided metal shield, and an outer plastic jacket. The shield gives better noise protection and higher bandwidth than twisted pair. Types: 50 ohm (baseband) and 75 ohm (cable TV).

3. Optical fibre

A thin strand of glass or plastic with three parts: the core (carries light), the cladding (glass of lower refractive index, which keeps light in the core by total internal reflection) and a protective jacket. Core diameters are about 8-10 µm (single mode) or 50-62.5 µm (multimode). Light pulses from an LED or laser carry the data.

✓ Answer checked by Claude Opus 5.5 (high effort)

Related questions

All Data Communication chapter 4 questions →