1. Transmission Media
⢠Guided
â Twisted Pair
â Cable
â Fiber
â Medium more important than the signal
⢠Unguided
â Atmosphere
â Outer Space
â Signal more important than the medium
3. Twisted Pair
⢠Two insulated copper wires in a spiral
⢠Number of pairs are bundled together
⢠Twisting decreases crosstalk
⢠Most common form for analog and digital
⢠Used in telephone system
⢠Subscriber loops
â From a personâs home to the local office of the phone company
⢠LANS
â 10Mbps with newer at 100Mbps
4. Twisted pair
⢠Long Distance
â 4 Mbps
â ISDN â Integrated Services Digital Network
⢠Digital
â Repeaters required every 2 â3 kilometers
⢠Analog
â Amplifiers required every 5-6 kilometers
â Bandwidth of 250KHz, carry a few voice channels
⢠Susceptible to noise, shielded and unshielded
⢠Compared to optical and coax twisted pair is limited in bandwidth,
distance, and data rate
5. Coaxial Cable
⢠Hollow outer cylindrical conductor surrounding a single
view
⢠Most versatile of mediums, used for TV, long distance
telephone,and LANâS
6. Coaxial Cable
⢠Part of long distance telephone network
⢠With FDM can carry over 10,000 voice channels
⢠Transmits both analog and digital signals
⢠Frequency characteristics superior to twisted pair
â Less susceptible to noise
⢠For long distance
â Amplifiers needed every few kilometers
â Repeaters needed every kilometer or so
7. Optical fiber
⢠Thin, flexible light passing material made from glass or
plastic
⢠Grouped into cables
8. Optical fiber
⢠Better than coaxial cable or twisted pair
⢠Data rates of 2Gbps over 10âs of Km
⢠Light weight â good for buildings
⢠Lower attenuation than coax or twisted
⢠Not effected by extreme electromagnetic fields
â Crosstalk and impulse
⢠Very difficult to tap â good security
⢠Applications
â Long Haul trunks, metro trunks, rural exchange trunks, more
recently beginning to displace twisted pair in subscriber loops and
in LANS
9. Optical Fiber
⢠Operates in range 10**14 to 10**15 Hz
â Infrared and visible spectrum
⢠Multimode
â Variety of angles of light will reflect and propogate
⢠Single Mode
â Radius of the core = order of a wavelength
â Only single angle passes
â Superior performance
⢠Two different light sources â both emit light when voltage applied
â LED â Light Emitting Diode â less costly, longer life
â ILD - Injection Laser Diode â greater data rate
10. Wireless
⢠Antennae
â Directional
⢠Focused EM beam
⢠The higher frequency the more focused
â Omnidirectional
⢠Lower frequency
⢠Spreads out to multiple receivers
⢠Three ranges of frequencies
â 26GHz â 40GHz --- microwave
â 30 MHz â 1GHz --- broadcast radio
â 3x10**11 to 2x10**14 Hz --- infrared
11. Terrestrial Microwave
⢠Parabolic dish
⢠Narrow beam â line of sight on towers to avoid obstacles
⢠Series of towers for long distance
⢠Applications:
â Long haul telephone
â Voice and TV
â Short point to point between buildings
⢠Main Source of loss
â Attentuation â especially with rainful
â Repeaters or amplifiers 10 to 100km
â Interference with overlapping bands
12. Satellite Microwave
⢠It is essentially a microwave relay station
⢠Uplink
â Receives transmission on one frequency
⢠Downlink
â Transmits on a second frequency
⢠Operates on a number of frequency bands known as
transponders
⢠Point to Point
â Ground station to satellite to ground station
⢠Multipoint
â Ground station to satellite to multiple receiving stations
13. Satellite Microwave
⢠Satellite orbit
â 35,784 Km, to match earth rotation
â Stays fixed above the transmitter/receiver station as earth rotates
⢠Satellites need to be separated by distance
â Avoid interference
⢠Applications
â TV, long distance telephone, private business networks
⢠Optimum frequency range
â 1 â 10 GHz
â Below 1GHz results in noise, above 10GHz results in severe attenuation
14. Broadcast Radio
⢠Omnidirectional unlike satellite
⢠Does not require dish like antennae
⢠Frequency range
â Radio - 3kHz to 300Ghz
â Broadcast radio â 30MHz to 1GHz
⢠Broadcast radio
â Transmission limited to line of sight
â Less sensitive to attenuation from rainfall than microwave
â Prime source of interference is multipath
15. Infrared
⢠Tranceivers must be within line of sight of each other or
via reflection
⢠Does not penetrate walls like microwave
⢠No frequency allocation or licensing