Amplitude:   The power variation in a signal which can vary with time, often measured in decibels (dB).

Analog Signals:   Any signals which can vary over a continuous range rather than in discrete steps.

ANSI (American National Standards Institute):   A private, non-profit organization that administers and coordinates the U.S. voluntary standardization and conformity assessment system.

Asymmetrical:   Different data speeds for upload versus download. For example 56K modems are asymmetrical in that the download speed is 56Kbps while the upload speed is 28.8Kbps or 33.6Kbps.

Asynchronous Communications:   A method of transmission in which data is sent without a specific timing mechanism between the sending and receiving devices.

Baud:   Denotes how often a signal changes per second, not to be confused with bps (bits per second). In older modems a single baud could carry one bit of data so baud rate did equal bps or data rate. However faster modems send multiple bits of data per baud and hence the baud rate and data rate can be vastly different.

Bell Standards:   U. S. modulation protocol standards developed by Bell Labs in the 1960s and 1970s to accommodate the networks at that time. Bell standards include Bell 103 (300bps), Bell 212A (1200bps), Bell 201B&C (2400bps) and Bell 208A& (4800 bps).

bps:   bits per second.

CCITT (Comite Consultatif International Telephonique et Telegraphique):   The International Consultative Committee for Telecommunications and Telegraphy is a United Nations organization that sets international communications standards. The CCITT has been known as the ITU since March 1, 1993.

CLEC (Competitive Local Exchange Carrier):   A telecommunications service provider which has no local access of its own by rents from the local exchange.

CO (Central Office):   A switching center that connects local copper loops to the core network in a given geographical area.

CODEC (COder-DECoder):   A device that converts analog signals into digital format for transmission and also converts received digital signals back into analog format.

DCE (Data Communications Equipment):   A communications device, such as a modem, that connects a DTE to the network.

Demodulator:   A device which decodes information from the carrier frequency of a transmission signal into digital data.

DTE (Data Terminal Equipment):   The computer or terminal that acts as a data source or destination connects to the network via a DCE.

Data Compression:   A method of reducing the amount of data that needs to be transmitted or stored by replacing redundant data with special coding.

Decibel (dB):   A logarithmic means of representing the ratio of two quantities such as input power to output power.

Demodulation :   The conversion of analog signals into digital signals.

Digital Signal:   A signal represented by a discrete set of levels. Often these levels take the form of on or off resulting in two discrete levels.

DSP (Digital Signal Processor):   A powerful and flexible method of processing analog signals in digital form.

Dual-line Modem:   A modem able to transmit at speeds up to 112Kbps by using two 56K modem chips on a single board that connects to two regular phone lines.

Full Duplex:   The ability to transmit both send and receive data at the same time. (Telephones are full duplex in that you can hear the person that you are talking to while you are talking.)

Guard Tone:   A 1800-Hz tone used in the United Kingdom and other countries to determine whether or not a PSTN circuit has the necessary bandwidth for a dial-up modem to transmit at high speed. Guard tones are not used in the United States.

Half Duplex:   The ability to send or receive data, but not simultaneously.

ITU (International Telecommunications Union):   A United Nations organization that sets international communications standards. The ITU was known as the CCITT previous to March 1, 1993.

K56flex:   A 56K modem protocol developed by Lucent and Rockwell that allows Lucent's V.flex2 and Rockwell's K56Plus technologies to interoperate.

K56Plus:   56Kbps modem protocol proprietary to Rockwell.

Kbps:   Kilobits per second. Equivalent to 1,024 bits per second.

Local Loop:   The twisted pair of copper wires and the associated terminating equipment that connects to the central office.

Modem (MOdulator/DEModulator):   A communications device that can encode digital data into a signal suitable for transmission and also decode a received transmission signal into digital data.

Modulator:   A device which codes digital data onto the carrier frequency of a transmission signal.

PBX (Private Branch eXchange):   A telephone switch at a customer site.

PCMCIA (Personal Computer Memory Card International Association):   A standard for small thin laptop expansion cards for modems, storage, and other devices. Often called PC cards.

POTS (Plain Old Telephone Service):   Basic analog telephone service which utilizes the bandwidth from DC up to 4 KHz.

Protocol:   A standardized set of rules that defines how two devices in a network will communicate with each other.

PSTN (Public Switched Telephone Network):   A public telephone network.

RBOC (Regional Bell Operating Company):   One of the seven US telephone companies that resulted from the break up of AT&T

RPI (Rockwell Protocol Interface):   A type of WinModem that is limited to 14.4Kbps connections.

Symmetrical:   Equal data speeds for both upload and download

Synchronous Communications:   A method of transmission in which data is sent at a specific timed rate via the mechanism a synchronizing or clocking signal between sending and receiving devices.

Topology:   The physical configuration of a communications network.

Transceiver:   A which transmits and receives data.

Trellis Coding:   Modulating data points on a constellation pattern in such a way that signals outside of specific regions are treated as line noise thereby increasing noise immunity.

Twisted-Pair Cable:   A pair of 18 to 24- gauge copper strands.

UART (Universal Asynchronous Receiver-Transmitter):   A controller chip in a modem that processes parallel digital data from a DTE into serial data for transmission and coming in and going out of the modem and vice versa.

V.32terbo:   19.2Kbps asynchronous communications protocol that is proprietary to AT&T.

V.32bis:   14.4Kbps ITU modem protocol standard.

V.34:   28.8Kbps and 33.6Kbps ITU modem protocol standard.

V.90:   56Kbps ITU modem protocol standard.

V.FC:   28.8Kbps modem protocol proprietary to Rockwell.

V.flex:   56Kbps modem protocol proprietary to Lucent.

Winmodems:   A modem design to use some of the processing power of the personal computer that it is connected to thereby reducing the amount of hardware required and the cost of the modem.

x2:   56Kbps modem protocol proprietary to U.S. Robotics.