Network Media by Fred Cohen

Typical media for networks include optical fibers, shielded and unshielded twisted wire pairs, coaxial cables, electromagnetic radio emanations, and ultrasound. These currently have approximate cost and performance characteristics as specified in the following table, but the extremely rapid changes in technology currently underway will undoubtedly make these figures invalid in the near future (they have changed twice during the last year). Bandwidth is given in bits per second (BPS), initial and ongoing costs are rated from 0 to 5, 0 being the cheapest for a typical installation.

 Media              Cost        Bandwidth    Ongoing
        ---------------------------------------------------
        fiber optics         2           50M BPS       2
        shielded pair        1           10M BPS       1
        unshielded pair      0            1M BPS       0
        coaxial cable        3          400M BPS       5
        radio                5         1000M BPS       4
        ultrasound           4           30K BPS       3

Fiber optics are difficult for an attacker to tap (although by no means impossible) compared to the other technologies, radio is more difficult to destroy but more susceptible to noise, unshielded wires have noise problems, and ultrasound is very susceptible to noise. Current computer to computer communications rarely take advantage of performance over 10M BPS because hardware (disks, processors, etc.) that uses this much bandwidth is expensive, and the rarity of applications requiring this bandwidth on an ongoing basis. In the case of voice data, each channel is about 40Kbaud, and for video data about 10MHz is required per signal.