ch 7. transmission media. transmission media (1) broad definition –anything that can carry...
TRANSCRIPT
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