Transmission media

Transmission media are the physical means by which a network moves signals from one device to another. They divide into guided media, where the signal follows a cable, and unguided media, where it travels through the air. Guided media include twisted-pair cable and coaxial cable, which carry electrical signals over copper, and fibre-optic cable, which carries light through glass or plastic. Unguided media include the radio used by Wi-Fi and cellular networks, point-to-point microwave, infrared and satellite links. The ISC2 exam outline names transmission media under secure network components in Domain 4, with physical security of media and signal propagation quality as its examples.

Each medium has its own security profile. Copper radiates emanations, can be tapped, and suffers from interference and crosstalk. Fibre radiates no electrical emanations and resists electromagnetic interference, and tapping it is harder and more likely to be noticed, though not impossible. Wireless signals reach beyond the building, so they depend on encryption and authentication rather than physical control. Every medium suffers attenuation over distance, and the signal-to-noise ratio limits how reliable a link can be.

Exam relevance: a scenario may give a requirement, such as resistance to interference or to eavesdropping in a sensitive area, and ask for the medium. Candidates are expected to match each medium’s physical properties to the risk.