Glossary

ADSL. Asymmetric digital subscriber line. An xDSL technology in which modems attached to twisted-pair copper wires transmit from 1.5 to 8 Mbps downstream (to the subscriber) and from 16 to 640 Kbps upstream, depending on the line distance, and signal amplitude.

ANSI. American National Standards Institute. The principal standards development body in the United States. It consists of voluntary members that represent the U.S. in the International Standards Organization (ISO). Membership includes manufacturers, common carriers, and other national standards organizations, such as the Institute of Electrical and Electronics Engineers (IEEE).

ATM. Asynchronous Transfer Mode. A switching technology that allows voice, data, image, and video traffic to be combined into evenly sized cells for high-speed transmission over one access circuit. Each 53 byte cell contains 48 bytes of payload and 5 bytes of control information.

Attenuation. The signal loss caused by a transmission channel at a particular frequency.

AWG. American Wire Gauge. A wire diameter specification; the lower the AWG number, the larger the wire diameter.

Backbone network. The major transmission path for network interconnection.

Bandwidth. The frequency band size of a signal.

Bridged taps. Unused twisted pair cables attached to a telephone subscriber loop.

Broadband. A communication channel with a bandwidth in excess of 1.54 Mbps.

CAP. Carrierless amplitude phase modulation. A version of quadrature amplitude modulation (QAM) that stores parts of a modulated message signal in memory and then reassembles the parts in the modulated wave. The carrier signal is suppressed before transmission because it contains no information and is reassembled at the receiving modem (hence the word "carrierless" in CAP).

CO. Central office. A facility that contains the lowest node in the hierarchy of switches that comprise the public telephone network.

Coaxial Cable. A cable consisting of one conductor, usually a small copper tube or wire, within and insulated from another conductor of larger diameter, usually copper tubing or copper braid.

Cross-talk. Interference caused by the coupling of two different signals, either on the same transmission line or on several lines.

CSA. Carrier Serving Area. A design guideline for the constraining of the length of telephone subscriber loops to accommodate digital telephone transmission equipment.

DMT. Discrete multi-tone modulation. A wave modulation scheme that discretely divides the available frequencies into 256 sub-channels or tones to avoid high-frequency signal loss caused by noise on copper lines.

Demodulation: The reverse of Modulation.

DSL. Digital subscriber line. A local loop access technology that calls for modems on either end of copper twisted-pair wire to deliver data, voice, and video information over a dedicated digital network.

DSLAM. Digital Subscriber Line Access Multiplexer. Multiplexing equipment that contains a high concentration of central office splitters, xDSL modems, and other electronics to connect traffic to the wide area network (WAN).

DWMT. Discrete Wavelet Multi-Tone. A variant of DMT modulation, DWMT goes a step further in complexity and performance by creating even more isolation between subchannels.

E1. The European basic multiplex rate that carries 30 voice channels in a 256-bit frame transmitted at 2.048 Mbps.

Echo cancellation. A technique used by ADSL, V.32, and V.34 modems that isolates and filters unwanted signal energy from echoes caused by the main transmitted signal.

ETSI. European Telecom Standards Institute. A consortium of manufacturers, service carriers, and others responsible for setting technical standards in the European telecommunications industry.

FDM. Frequency division multiplexing. A technique that divides the available bandwidth of a channel into a number of separate channels.

FEXT. Far End Crosstalk. The crosstalk noise coming from the other end of the twisted pair telephone loop.

HDSL. High bit-rate digital subscriber line. A xDSL technology in which modems on either end of two or more twisted-pair lines deliver symmetric T1 or E1 speeds. Currently, T1 requires two lines and E1 requires three.

HDTV. High-definition television. A system of transmitting television signals at 24 Mbps, which increases the horizontal lines of resolution from 480 to 560 lines per display.

ISDN. Integrated Services Digital Network. A digital subscriber line network with circuit and packet switching capabilities for voice and data communications at data rates of up to 1.544 or 2.048 Mbps.

ISO. International Standards Organization.

ISP. Internet service provider.

ITU. International Telecommunications Union. An international standards body, formerly called the CCITT.

LAN. Local area network. A type of broadcast network, covering a limited area, in which computers and other devices are attached to a common transmission medium.

Load coils. Inductance coils used in telephone loops to improve the transmission performance of the voice band channel.

Local loop. The line from a subscriber to the telephone company central office.

Modem. Contraction for modulator/demodulator. A modem converts the serial digital data from a transmitting device into a form suitable for transmission over the analog telephone channel.

Modulation. The process in which the characteristics of one wave or signal are varied in accordance with another wave or signal. Modulation can alter frequency, phase, or amplitude characteristics.

Multiplex. Combining signals of multiple channels into one channel. This process provides multiple users with access to a single conductor or medium by transmitting in multiple distinct frequency bands (frequency division multiplexing, or FDM) or by assigning the same channel to different users at different times (time division multiplexing, or TDM).

NEXT. Near End Crosstalk. Crosstalk noise coming from near-end transmitter.

Optical fibres. offer the communication system designer a channel bandwidth that is several of magnitude larger than coaxial cable channels. The transmitter or modulator is a light source, either LED or laser. Information is transmitted by varying (modulation) the intensity of the light source with the message signal. The light propagates through the fibre as a light wave and is amplified periodically along the transmission path to compensate for signal attenuation. At the receiver, the light intensity is detected by a photodiode. (Proakis & Salehi, 1994, p. 14)

POTS. Plain old telephone service.

POTS splitter. A passive filter that separates voice traffic from data traffic.

PSTN. Public switched telephone network. A telephone system through which users can be connected by dialing specific telephone numbers.

QAM. Quadrature amplitude modulation. A bandwidth conservation process routinely used in modems, QAM enables two digital carrier signals to occupy the same transmission bandwidth.

R-ADSL. Rate-adaptive digital subscriber line. An emerging variation of CAP; it divides the transmission spectrum into discrete sub-channels and adjusts each signal transmission according to line quality.

SDSL. Single-line digital subscriber line. SDSL is essentially HDSL over a single twisted pair.

Subscriber loop. The physical medium connecting the subscriber to the central office.

T1. A 1.544 Mbps line; the same as DS1.

TDM. Time division multiplexing. A digital transmission method that combines signals from multiple sources on a common path. This common path is divided into a number of time slots and each signal or channel is assigned its own intermittent time slot, allowing the path to be shared by multiple channels.

Trellis Coded Modulation. A combination of a specially selected convolution code and a bit-to-symbol mapping algorithm for achieving significant coding gain with no bandwidth expansion.

Twisted-pair. Telephone system cabling that consists of copper wires loosely twisted around each other to help cancel out any induced noise in balanced circuits.

VDSL. Very high bit-rate digital subscriber line. A technology in which modems enable access and communications over twisted-pair lines at a data rate from 1.54 Mbps to 52 Mbps. VDSL has a maximum operating range from 1,000 feet to 4,500 feet on 24-gauge wire.

VoD. Video-On-Demand. Similar to functions of video recorders, VoD services provide its users with real-time interaction such as ‘play’, ‘rewind’, and ‘fast forward’.

WAN. Wide area network. A geographically dispersed network.

xDSL. The "x" represents the various forms of digital subscriber line (DSL) technologies: ADSL, R-ADSL, HDSL, SDSL, or VDSL.