Introduction to Data Communications |
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13. Modems (cont'd) |
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There are many types of modems, the most common are:
- Optical Modems
Uses optical fibre cable instead of wire. The modem converts the digital signal to pulses of light to be transmitted over optical lines. (more commonly called a media adapter or transceiver)
- Short Haul Modems
Modems used to transmit over 20 miles or less. Modems we use at home or to connect computers together between different offices in the same building.
- Acoustic Modem
A modem that coupled to the telephone handset with what looked like suction cups that contained a speaker and microphone. Used for connecting to hotel phones for travelling salespeople.
- Smart Modem
Modem with a CPU (microprocessor) on board that uses the Hayes AT command set. This allows auto-answer & dial capability rather than manually dialing & answering.
- Digital Modems
Converts the RS-232 digital signals to digital signals more suitable for transmission. (also called a media adapter or transceiver)
- V.32 Modem
Milestone modem that used a 2400 Baud modem with 4 bit encoding. This results in a 9600 bps (bits per second) transfer rate. It brought the price of high speed modems below $5,000.
Baud is the speed at which the Analog data is changing on the Voice Channel and bps is the speed that the decoded digital data is being transferred.