Physical Media Now that we’ve been over how to encode data as signals, what are the physical media that carry these signals?

Guided media Twisted-pair: Standard phone cable Two insulated wires wrapped around each other One carries the signal; the other is a ground reference Twisting reduces the effects of noise and crosstalk Used for phone lines, T1, etc.

Coaxial cable Carries higher frequencies than twisted pair Consists of an inner wire that carries the signal and an outer sheath that serves as the ground reference. Used in cable TV, ethernet

Fiber optic Glass or plastic core surrounded by a cladding. Difference in density between core and cladding allows light to bounce its way down the cable. Different fibers can support different transmission modes: –Multimode: Multiple beams of light traveling different paths. –Single-mode: Uses a single beam projected as close to horizontally as possible. Very high bandwidth and very low attenuation.

Unguided media