Dialup UK Article - Distinguish Between External Modems
The word "modem" is a contraction of the words
modulator-demodulator. A modem is typically used to send digital
data over a phone line in analog form. The sending modem modulates
the data into a signal that is compatible with the phone line,
and the receiving modem demodulates the signal back into digital
data compatible with the computer. This is standard for of
data conversation used for all modems that uses phone lines
for connect through Internet. Some advanced modems like wireless
modems do not use phone lines. They convert digital data into
radio signals and back.
There is one standard interface for connecting external modems
to computers called RS-232. Accordingly, any external modem
can be attached to any computer that has an RS-232 port.
Now days, almost all personal computers comes with RS-232
ports. Hence, the problem with the compatibility is resolved
in most cases as far as external modems are concerned. However,
certain other features distinguish modems from each other.
The major feature is Internet protocol used for data transfer.While
the modem interfaces are standardized, a number of different
protocols for formatting data to be transmitted over telephone
lines exist. Some Internet protocols are official standards,
while private companies develop some others. Internet protocols:
Most modems have built-in support for the most common protocols.
At slow data transmission speeds at least, most modems can
communicate with each other with Standard Internet protocols.
At high transmission speeds, however, the protocols are less
standardized. Aside from the transmission protocols that they
support, following are some other important features that
distinguish one modem from another.
Let us discuss them…
A modem is traditionally built to support data transfer However,
Many modems support a switch to change between voice and data
modes. In data mode, the modem acts like a regular modem and
transfers only data. In voice mode, the modem acts like a
telephone and also support verbal communication. Modems that
support a voice/data switch have a built-in loudspeaker and
microphone for voice communication.
Another distinguishing feature is the data compression technique
used. 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. Most of the modern modems fulfill
The speeds of data transfer also another distinguishing feature
and play a major role at times. Many people going to purchase
modem will emphasize on how fast the modem can transmit and
receive data. The units for measurement are also different
for slow and faster modems. Sped of slower modems are measured
in terms of baud rates. The slowest rate is 300 baud At higher
speeds, modems are measured in terms of bps or kbps of bits
per second (bps) Kilo bits per second kbps. The fastest modems
run at 56 Kbps or 57,600 bps, although they can achieve even
higher data transfer rates by compressing the data.
Apart from these features, some modern modems also come with
flash memory rather than conventional ROM, which means that
the communications protocol can be easily updated if necessary.