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Modems
By Mahesh Rathod

Modems are the must-have accessories to browse the Net the old fashioned way. We give you a lowdown on these devices

A modem is a device that can connect one computer to another across ordinary telephone lines

A modem is a device that can connect one computer to another across ordinary telephone lines. The current telephone system is incapable of carrying the voltage changes required for a direct digital connection. A modem overcomes this limitation by modulating digital information into audio tones for transmission across the phone line and by demodulating those tones back into digital information upon reception. It is from these actions that the name MODEM is derived (Modulate, Demodulate).

How do modems work?
Almost everyone accessing the Net is connecting using a modem. Everybody knows that modems are used to connect to the Internet, but do you know how they do it? For instance, computers operate in the digital world, but telephone lines require a different method of transmission. The modem is what handles this conversion. Modem stands for modulator-demodulator. The modem modulates the signal into a sine wave. This in turn can be broadcast over a telephone line. The signal is transmitted over the line until it reaches the IP hub. At this point, the sine is demodulated into a digital signal once more, and the connection with the Internet is complete. Modems can do this at a variety of speeds depending on the technology and availability of access lines.

Features

Speed ITU Standards Uses
14.4 Kbps V.32 bis For sending and receiving e-mail or faxes.
28.8 Kbps V.34 If you have noisy telephone lines, it makes sense to get a modem faster
than 28.8 Kbps.    
33.6 Kbps V.34 bis If your ISP lacks digital telephone connections, 33.6 Kbps is as fast as you'll go
56 Kbps V.90 (also K56flex, X2) 56K modems are the standard now, but there are caveats.

There are number of features you need to consider when buying a modem.

Bits Per Second (BPS): This is the rate at which a modem can transmit and receive data. At slow rates, modems are measured in terms of baud rates. The slowest rate is 300 baud (about 25 cps). At higher speeds, modems are measured in terms of bits per second (bps). The fastest modems run at 57,600 bps, although they can achieve even higher data transfer rates by data compression. Obviously, the faster the transmission rate, the faster you can send and receive data.

Voice/data: Many modems support a switch to change between voice and data modes. In data mode, the modem acts like a regular modem. In voice mode, the modem acts like a regular telephone. Modems that support a voice/data switch have a built-in loudspeaker and microphone for voice communication.

Auto-answer: An auto-answer modem enables your computer to receive calls in your absence. This is only necessary if you are offering some type of computer service that people can call in to use.

Data compression: Some modems perform data compression, which enables them to send data at faster rates. However, the modem at the receiving end must be able to decompress the data using the same compression technique.

Flash memory: Some modems come with flash memory rather than conventional ROM, which means that the communications protocols can be easily updated if necessary.

Modem type: Internal, External or PCMCIA

Internal modems come on a card that plugs into your PC's bus. An internal modem contains its own serial port onboard, and uses your PC's power supply. External modems are normally self-contained in their own case (or may be rack-mounted in commercial versions), have their own power supply, and connect to your computer via a serial cable to one of the serial ports on the back of your PC.

Each of these comes with its own advantages.

Internal Modems: They are easy to install, generally less expensive as they don't come in a case, does not have its own power supply (it takes from the PC itself), less prone to people messing around with them, no cables to get knocked loose and consume no desktop space.

External Modems: These modems incorporate a panel of lights, LEDs, or a LCD to display information about the current session, and can aid in problem diagnosis and resolution. Can be powered on and off to reset independently from your computer. More easily moved (for example, you could use the same external modem with your desktop machine and your laptop). Externals often also have a volume control, which lets you adjust the speaker volume very quickly and easily.

PCMCIA Modems: PCMCIA (or "PC Card") modems form offer portability. PCMCIA modems come in the form of a thin card that fits into a PCMCIA slot-most laptops have one. Due to its sheer size and the convenience that it offers, PCMCIA modems are meant for people on the move.

Speed
The most important parameter while choosing any modem is the rate at which it can send and receive information. In general, buy the fastest possible modem. Modem speeds range from 14.4 Kbps to a theoretical maximum of 56 Kbps. Now 56 Kbps modems are the common standard, with lower speed modems more or less obsolete.

Fax Modems
Modems have the added ability to send and receive facsimiles over the past couple of years. However, you need to keep in mind that a fax modem is no substitute for a real fax machine. If you are a heavy user of fax technology, don't expect a fax modem to handle your faxing needs. If, on the other hand, you occasionally need to fire off a fax, a fax modem is a wonderful device. For sending important letters late at night from your home, a fax modem is the right choice.

Mahesh Rathod can be reached at rathodmp@hotmail.com
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