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ATM cell is an information packet containing 53 bytes of data traffic and additional ''overhead" defining the virtual circuits and paths over which the data are to be transmitted.

Bandwidth is the part of a frequency band occupied by a communications channel. Sometimes the term is used to describe the number of bits per second transmitted in a channel.

Bent pipe is a satellite communications system that transmits to an Earth station essentially the same signal it receives from another Earth station.

BER (bit-error rate) is the probability that a bit is received in error.

Bit is a binary unit of information.

bps (bits per second) refers to the speed at which data is generated by a source or transmitted over a communications channel. Measurements are often stated in units of 103 bits per second (kilobits or kbps) or 106 bits per second (megabits or Mbps).

Byte is a unit of 8 bits.

C4I (command, control, communications, computing, intelligence) is a military concept encompassing all the functions and capabilities sought in an advanced communications system.

CDMA (code division multiple access) is a technique that allows many users to share the same radio spectrum. A sequence of pseudo-random bits, known as a code, spreads the information signal over a much larger range of frequencies than is occupied by the original information signal. See FDMA, TDMA, spread spectrum.

CDPD (cellular digital packet data) is a packet-switched network that uses one or more channels in an analog cellular telephone system.

Cell refers to a geographic region within which cellular telephone subscribers can communicate with a particular base station (site). Cell radius ranges from 0.5-15 kilometers depending on the density of the subscribers and the extent of topological obstructions.

CELP (code excited linear prediction) is a technique for encoding voice.

CMOS (complementary metal oxide semiconductor) is an inexpensive, low-power integrated circuit technology.

CONDOR is a National Security Agency program designed to develop and demonstrate secure voice and secure net broadcast services, using STU III-compatible units, over the commercial cellular infrastructure.

COTS (commercial off-the-shelf) refers to readily available commercial technologies and systems.

CSMA/CD (carrier-sense multiple access with collision detection) is a