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– 19th century – telegraph by Morse– 1869 – telephone by Bell– 1895 – wireless communication by Hertz–Modern communication media – twisted-

pair, coaxial cable, and optical fiber

• Classification

Telegraph

http://www.youtube.com/watch?v=Lki3jxNLVCI

Twisted-pair Cable

• Two metal conductors: one for signal, the other for reference (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 UTP– Central core conductor and outer con-

ductor

Categories of coax-ial 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: Wire-less

• Transport electro-magnetic waves without using 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