Modem Terms

Modem definitions 101

Modem

A modem is a device that modulates and demodulates data. Data is modulated by the modem on the sending end and then sent via telephone line, cable, or radio frequency to a receiving modem that demodulates the data.

BPS

BPS, or bits per second, is the speed at which a modem transmits and receives data. The earliest modems were so slow that their speed was measured in terms of bauds rather than bits. Today's modem speeds are also displayed as kbit/s, or kilobits per second.

Data compression

An encoding technique that reduces the number of bits sent, allowing a modem to send more information in a shorter time. The sending and receiving modems must be using the same data compression technique. ZIP files are one form of data compression.

Duplex

Meaning two-way, it's the manner in which modems transmit data. In half duplex transmissions, modems alternate sending and receiving data. In full duplex transmissions, both modems send and receive simultaneously, so information travels both directions at once.

Modes

Modems have different modes: command mode (also known as local or terminal mode), and online mode (also known as data mode). There are also originate mode and answer mode.

In command mode, the modem understands any information it receives as modem commands, tries to perform them, and returns results.

In online mode, the modem understands all information as data.

Originate mode is when a modem is calling another computer.

Answer mode is when a modem is expecting or receiving a call.

Modem speed test

Modem speed tests are pages available online that measure how quickly a test page is loaded and displayed on your browser. A modem speed test can determine the current speed or data transfer rate of your modem.

Types of modems

Cable Modem
A modem that uses the available bandwidth on cable TV lines to transmit and receive data. Greater data transmission speeds can be attained with cable modems because TV coaxial cable permits greater bandwidth usage than with standard phone line modems.

DSL Modem
DSL modems, also known as ADSL modems for asymmetric digital subscriber line, are modems that use standard copper phone lines for data transmission. Unlike modems that use voice bandwidth only, DSL modems use additional bandwidth capacity in the phone lines for data transmission, resulting in faster transmission speeds.

Fiber Optic Modem
Fiber optics is a technology that uses glass or plastic threads, also called fibers, to transmit data. Fiber optic cables are made up of clusters of these fibers, which are each capable of transmitting messages modulated onto light waves.

Fiber provides both greater bandwidth than copper wires and also greater data security because its signals are not electrical and therefore not detectable from a remote location. Fiber optic modems are typically smaller and lighter than standard modems.

Wireless Modem
Wireless modems are used to connect a computer to a wireless local area network, or WLAN. Wireless modems use radio frequencies to connect to a local access point.

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