Free 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 this requirement.

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.