Modems
Although digital telephone lines are gaining popularity, millions of homes and businesses still have only analog telephone lines. Attaching a computer to an analog telephone line requires a modem.
A computer’s “voice" is digital; that is, it consists of on/off pulses representing 1's and O's. A device called a modem (short for modulator demodulator) is needed to translate these digital signals into analog signals that can travel over standard telephone lines.
In its modulation phase, the modem turns the computer’s digital signals into analog signals, which are then transmitted across the phone line. The reverse takes place during its demodulation phase, as the modem receives analog signals from the phone line and converts them into digital signals for the computer.
A modem’s transmission speed (die rate at which it can send data) is measured in bits per second (bps).
Today’s fastest modems for dial-up connections on standard phone lines have a maximum theoretical transmission speed of 56,000 bits per second, or 56 kilobits per second (Kbps), and are called 56K modems. The 56K modem’s speed is due to several factors, such as the modem’s use of the V.90 or newer V.92 data communications standards.
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The different types of modems are as follows:
1. External Modem:
An external modem is a box that houses the modem's circuitry outside the computer. It connects to the computer using a serial, USB, or FireWire port, and then connects to the telephone system with a standard telephone jack.
2. Internal Modem:
An internal modem is a circuit board that plugs into one of the computer's expansion slots. An internal modem saves desktop space but occupies an expansion slot.
3. Fax modems:
Fax modems can exchange faxes with any other fax modem or fax machine. With the proper software, users can convert incoming fax files into files that can be edited with a word processor— something that stand-alone fax machines cannot do.
4. ISDN Modem:
The ISDN modem requires a special phone line called an ISDN line. This modem sends data at a very fast rate. (56K). The advantage of this modem is that it is very fast and is able to transfer data and graphics at an amazing speed with very little interference. These modems and lines tend to be quite expensive.
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