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Chapter 5 notes 233

Chapter 5 notes 233 - Chapter 5 Physical Layer Propagation...

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Chapter 5: Physical Layer Propagation Signal and Propagation o Received signal is changed by propagation affects Attenuation : Loss of signal strength because of range, interference or wire size Noise : unwanted electrical or electromagnetic energy that degrades quality of signals and data Signal To Noise Ratio : (SNR) measure of signal strength relative to background noise o Signaling : Analog : Signal rises and falls smoothly in intensity small propagation errors are not fixed Binary : Two states per clock cycle ** most transmission is binary ** Small propagation effects don’t create errors in reading the signal Digital : a few states per clock cycle Can transmit multiple bits per cycle Less error immunity to propagation errors than binary o Antennas Omnidirectional : radiates power in all directions in one plane, with power decreasing with elevation angle above or below the plane Ex : radio broadcasting, cell phones, wifi, cordless phone, GPS Directional : Radiates power in one or more directions allowing for increased performance on transmit and reduced interference from unwanted sources Ex : TV antennas, cellular repeaters, satellite TV o Duplexes Full-Duplex Allows communication in both directions simultaneously o Ex : Land-line telephone networks, mobile phones (callers can speak and be heard at the same time ) Full-Duplex Ethernet makes simultaneous use of two physical pairs of twisted cables Half-Duplex Provides communication in both directions, but one at a time ( not simultaneously ) Once a party begins receiving a signal, must wait for transmitter to stop transmitting before replying o Ex
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