Ch 7. Transmission Media

Transmission Media (1) Broad definition –Anything that can carry information In data communication: –Free space, metallic cable, fiber-optic cable

Transmission Media (2) History –19 th century – telegraph by Morse –1869 – telephone by Bell –1895 – wireless communication by Hertz –Modern communication media – twisted-pair, c oaxial cable, and optical fiber Classification

Telegraph CI

Twisted-pair Cable Two metal conductors: one for signal, the other for refere nce (ground) –Twisted for the equal amount of exposure of each line to the noise Unshielded twisted-pair (UTP) vs. shielded twisted-pair ( STP)

Categories of UTP cables

UTP Performance

Coaxial Cable Carry signals of a higher frequency than U TP –Central core conductor and outer conductor Categories of coaxial cables

Coaxial Cable Performance

UTP vs. Coaxial Coaxial cables UTP

Fiber-Optical Cable Bending of light ray Guide light ray

Optical Fiber Performance Better performance than Coaxial and UTP (1/10) Provide cost-effective solution for data transfer –Using WDM, at a rate of 1600 Gbps

7.2 Unguided Media: Wireless Transport electro-magnetic waves without u sing a physical conductor –Propagation methods

Wireless Transmissions Radio waves (3K ~ 1GHz) –Long-distance, low rate communication –Radio, TV, paging Microwaves (1G ~ 300GHz) –Short-distance, high rate communication –Cellular, satellite, wireless LANs Infrared waves (300G ~ 400THz) –Very short range communication –Line-of-sight is required –In-door communication (e.g. remote controller)

Antennas Omni-directional (directionless) Uni-directional