Coaxial cable

Coaxial cable carries signals on a single copper conductor at its centre, surrounded in turn by an insulating layer, a braided or foil conductive shield, and an outer jacket. The shield keeps external electromagnetic interference out and reduces what the cable radiates, so coaxial cable resists interference better than unshielded twisted pair.

Early Ethernet ran over coaxial cable in a bus topology, in the thick and thin variants known as 10Base5 and 10Base2. Every station shared one cable, the ends needed terminators, and a single break or a missing terminator could take down the whole segment. Twisted pair and fibre optic cable have since replaced it for local networks, and coaxial cable survives mainly in cable television, cable broadband and some radio links. For security, shielding reduces emanations but does not remove them, and copper can be tapped by someone with physical access, which is why fibre is usually preferred where tapping or emanation is the concern. Both points fall under transmission media in the exam outline.

Exam relevance: a scenario is likely to compare cable types by resistance to interference, ease of tapping or failure behaviour. Candidates are expected to place coaxial cable between unshielded twisted pair and fibre on interference, and to link it with bus topologies and their single point of failure.