are are those those that that provide provide a a conduit conduit from from one one device device to to another, another, include include twisted twisted- -pair pair cable, cable, coaxial coaxial cable, cable, and and fiber fiber- -optic optic cable cable. .
wire / optical fibre Unguided Unguided - - wireless wireless Characteristics and quality determined by Characteristics and quality determined by medium and signal medium and signal medium and signal medium and signal in unguided media in unguided media - - bandwidth produced by bandwidth produced by the antenna is more important the antenna is more important in guided media in guided media - - medium is more important medium is more important Key concerns are data rate and distance Key concerns are data rate and distance
data rate higher bandwidth gives higher data rate Transmission impairments Transmission impairments eg. attenuation eg. attenuation eg. attenuation eg. attenuation Interference Interference Number of receivers in guided media Number of receivers in guided media more receivers introduces more attenuation more receivers introduces more attenuation
is used only as a ground reference. The receiver uses the difference b/w the two levels. Twisting increases the probability that both wires are probability that both wires are effected by the noise in the same manner, thus the difference at the receiver remains same. Therefore, number of twists per unit length determines the quality of the cable.
analog analog needs amplifiers every 5km to 6km needs amplifiers every 5km to 6km digital digital can use either analog or digital signals can use either analog or digital signals needs a repeater every 2 needs a repeater every 2- -3km 3km needs a repeater every 2 needs a repeater every 2- -3km 3km limited distance limited distance limited bandwidth (1MHz) limited bandwidth (1MHz) limited data rate (100MHz) limited data rate (100MHz) susceptible to interference and noise susceptible to interference and noise
Telephone lines connecting Telephone lines connecting subscribers to the central office subscribers to the central office DSL lines DSL lines LAN LAN – – 10Base 10Base- -T and 100Base T and 100Base- -T T LAN LAN – – 10Base 10Base- -T and 100Base T and 100Base- -T T
telephone transmission Can carry 10,000 voice calls Can carry 10,000 voice calls simultaneously Short distance computer systems links Local area networks
superior frequency characteristics to TP superior frequency characteristics to TP performance limited by attenuation & performance limited by attenuation & noise noise analog signals analog signals analog signals analog signals amplifiers every few km amplifiers every few km closer if higher frequency closer if higher frequency up to 500MHz up to 500MHz digital signals digital signals repeater every 1km repeater every 1km closer for higher data rates closer for higher data rates
Applications: Applications: Analog telephone networks Analog telephone networks Cable TV networks Cable TV networks Traditional Ethernet LAN Traditional Ethernet LAN
greater capacity data rates of hundreds of Gbps data rates of hundreds of Gbps smaller size & weight smaller size & weight lower attenuation lower attenuation lower attenuation lower attenuation electromagnetic isolation electromagnetic isolation greater repeater spacing greater repeater spacing 10s of km at least 10s of km at least
uses total internal reflection to transmit uses total internal reflection to transmit light light effectively acts as wave guide for 10 effectively acts as wave guide for 1014 14 to 10 to 1015 15 Hz Hz Hz Hz can use several different light sources can use several different light sources Light Emitting Diode (LED) Light Emitting Diode (LED) cheaper, wider operating temp range, lasts longer cheaper, wider operating temp range, lasts longer Injection Laser Diode (ILD) Injection Laser Diode (ILD) more efficient, has greater data rate more efficient, has greater data rate relation of wavelength, type & data rate relation of wavelength, type & data rate
is 3kHz to 300GHz use broadcast radio, 30MHz use broadcast radio, 30MHz - - 1GHz, for: 1GHz, for: FM radio FM radio UHF and VHF television UHF and VHF television UHF and VHF television UHF and VHF television is omnidirectional is omnidirectional still need line of sight still need line of sight suffers from multipath interference suffers from multipath interference reflections from land, water, other objects reflections from land, water, other objects
for long haul telecommunications and short point and short point- -to to- -point links point links requires fewer repeaters but line of sight requires fewer repeaters but line of sight use a parabolic dish to focus a narrow beam use a parabolic dish to focus a narrow beam use a parabolic dish to focus a narrow beam use a parabolic dish to focus a narrow beam onto a receiver antenna onto a receiver antenna 1 1- -40GHz frequencies 40GHz frequencies higher frequencies give higher data rates higher frequencies give higher data rates main source of loss is attenuation main source of loss is attenuation distance, rainfall distance, rainfall also interference also interference
relay station receives on one frequency, amplifies or repeats receives on one frequency, amplifies or repeats signal and transmits on another frequency signal and transmits on another frequency eg. uplink 5.925 eg. uplink 5.925- -6.425 GHz & downlink 3.7 6.425 GHz & downlink 3.7- -4.2 GHz 4.2 GHz typically requires geo typically requires geo- -stationary orbit stationary orbit typically requires geo typically requires geo- -stationary orbit stationary orbit height of 35,784km height of 35,784km spaced at least 3 spaced at least 3- -4 4° ° apart apart typical uses typical uses television television long distance telephone long distance telephone private business networks private business networks global positioning global positioning
end line of sight (or reflection) end line of sight (or reflection) are blocked by walls are blocked by walls no licenses required no licenses required no licenses required no licenses required typical uses typical uses TV remote control TV remote control IRD port IRD port
conductor used to radiate or collect electromagnetic energy electromagnetic energy transmission antenna transmission antenna radio frequency energy from transmitter radio frequency energy from transmitter converted to electromagnetic energy byy antenna converted to electromagnetic energy byy antenna converted to electromagnetic energy byy antenna converted to electromagnetic energy byy antenna radiated into surrounding environment radiated into surrounding environment reception antenna reception antenna electromagnetic energy impinging on antenna electromagnetic energy impinging on antenna converted to radio frequency electrical energy converted to radio frequency electrical energy fed to receiver fed to receiver same antenna is often used for both purposes same antenna is often used for both purposes
Low 1-100M High High Low STP Medium 1-150M High Medium Low Coax Medium 1M–1G Medium Medium Low Coax Medium 1M–1G Medium Medium Low Fibre High 10M–2G Low Low High Radio Medium 1-10M Varies High Low Microwv High 1M–10G Varies High Medium Satellite High 1 M–10G Varies High Medium Cellular High 9.6–19.2K Low Medium Low
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