1. Modems Problem –Computer is digital –Telephone line is analog –Need translation device called a modem Digital Signal Modem Analog Signal

2. 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) Digital Device Analog Transmission Line

3. 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 Digital Signal Modem Analog Signal

4. Modulation Example: Frequency Modulation –1 is a high-frequency vibration –0 is a low-frequency vibration 1 0 1 1

5. 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

6. 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

7. 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

8. Modem Connection for Internal Modem Phone Line to Telephone Phone Line to Wall Jack

9. Modem Connection for External Modem Phone Line to Telephone Wall Power: usually uses “brick” transformer Serial Cable to Serial Port Phone Line to Wall Jack