A modem is a device that allows a computer to be "connected" to another computer via an analog phone line. The word modem comes from MODulator DEModulator, which means that the digital data from a computer is transformed into analog data that can be transmitted over a phone line.

Criteria for choosing a modem

• Transmission Speed
• Data Compression
• Error Correction
• Internal vs. External

The most important decision in choosing a modem is the transmission speed. When modems first came out, the speed was measured in a baud rate. Nowadays, the transmission speed is measured in a bps (bits per second) rating.

Standard Speeds

When modem manufacturers found ways to build data compression capabilities, modem speeds increased. Data compression uses mathematical algorithms to analyze groups of bits and represents it with shorter groups of bits. It soon became evident that modems needed a standard to understand the compession schemes of other modems. The first standard was V.32, which allowed modems to acheive speeds of 9600 bps. Later, the V.32 standard was improd upon and evolved into V.32bis, handling speeds up to 14400 bps. Following V.32bis came V.34, which is used most frequently by 28800 bps modems.

When computers communicate through telephone lines, even the smallest degree of static can corrupt all the electric impulses. As a result, modems and communications software use error control to retrieve these transmission errors. Standard error control protocols are: MNP2, MNP3, MNP4, MNP5, and V.42bis(incorporating all the protocols).

The last decision when choosing a modem is if you want external or internal.

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