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
