Modems Problem –Computer is digital –Telephone line is analog –Need translation device called...
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Modems • Problem – Computer is digital – Telephone line is analog – Need translation device called a modem Digital Signal Modem Analog Signal
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Transcript of Modems Problem –Computer is digital –Telephone line is analog –Need translation device called...
Modems
• Problem– Computer is digital– Telephone line is analog– Need translation device called a modem
DigitalSignal
Modem
AnalogSignal
Modems• Note:
– Device is digital;Transmission line is analog
– Cannot just say “modem translates between analog and digital” (For analog device and digital transmission line, need something else)
DigitalDevice
AnalogTransmission Line
Modulation
• A Modem is a Modulator and Demodulator
– Modulation is converting outgoing digital device signals into analog transmission line signals
– Demodulation is converting incoming analog transmission line signals into digital device signals
DigitalSignal
Modem
AnalogSignal
Modulation
• Example: Frequency Modulation– 1 is a high-frequency vibration– 0 is a low-frequency vibration
1
0
1
1
Modem Forms
• Internal Modem– On printed circuit board inside PC– Does not take up desktop space– Can be complex to install--must open up
computer
Modem Forms• External Modem
– Easy to install (just plug into serial port)– Takes up desk space– Needs wire to serial port (adds to wiring
clutter)– Needs electrical power
Modem Forms• PC Card Modems
– Fit in PC Card slots on notebooks– Easy to install– Do not take up desktop space– Expensive– Few desktop PCs have PC Card slots
Modem Connection for Internal Modem
Phone Line toTelephone
Phone Line toWall Jack
Modem Connection for External Modem
PhoneLine to
Telephone
Wall Power:usually uses
“brick” transformer
Serial Cableto Serial
Port
Phone Line toWall Jack
