Glossary
Symbol
2B1Q (2 bits, 1 quarternary)—A line code at layer one for the BRI U interface. Two bits of data (2B) are mapped into one of four line values (1Q, or 1quarternary). This coding scheme allows a single copper pair to carry 160 Kbps of information bidirectionally and simultaneously at a distance of up to three miles.
A
ACK (acknowledgement code)— A communications code sent from a receiving modem to a transmitting modem to indicate that it is ready to accept data. It is also used to acknowledge the error-free receipt of transmitted data. Contrast with NAK.
address—A numbered location inside a computer. The computer uses addresses to access resources such as video cards, USB ports, memory, etc.
analog signal—A waveform that has amplitude, frequency, and phase, which takes on a range of values between its maximum and minimum points.
analog transmission—A type of telecommunications that uses an analog signal as a carrier of voice, data, video, etc. An analog signal becomes a carrier when it is modulated by altering its phase, amplitude, and/or frequency to correspond with the source signal. Compare with digital transmission.
API (application program interface)—A software module created to allow dissimilar, or incompatible applications programs to transfer information over a communications link. APIs may be simple or complex; they are commonly required to link computer applications with mainframe programs.
ASCII (American Standard Code for Information Interchange)— Pronounced ass-key. A binary code for data that is used in communications and in many computers and terminals. The code is used to represent numbers, letters, punctuation, and control characters. The basic ASCII code is a 7-bit character set, which defines 128 possible characters. The extended 8-bit ASCII code defines 255 characters.
ASI (application services interface)— A software module that creates the interface between a LAN-connected PC and the network operating system. ASIs packetize computer data for transport over the network. NASI, NCSI, MCSI and NETCI are specific examples.
AT commands—A standard set of commands used to control modems. Each AT command string begins with the characters AT, which get the attention of the modem before the actual command is issued. See also command mode.
B
background—An activity that takes place in the computer while you are running another application. In other words, the active user interface does not correspond to the background task.
bandwidth—The transmission capacity of a computer channel, communications line or bus. It is expressed in cycles per second (hertz), the bandwidth being the difference between the lowest and highest frequencies transmitted. The range of usable frequencies that a transmission medium will pass without unacceptable attenuation or distortion. Bandwidth is a factor in determining the amount of information and the speed at which a medium can transmit data or other information.
basic access—A term that describes a simple standardized combination of access channels that constitute the access arrangements for most ISDN users.
B-channel(bearer channel)— A 64 Kbps ISDN channel used for digital high-speed data or voice transmission. Simultaneous voice and data transmission requires subscription to two B-channels. A voice call can be placed or received while a data call is in process (or vice versa); however, two simultaneous voice or two simultaneous data calls are not supported.
bearer capability (BC)— The level of functionality provided by the ISDN B-channel (e.g., data, 3.1 KHz audio, etc.).
bearer services—A set of ISDN functions provided by the B-channel, such as digital telephony, toll-free inbound/outbound calls, 64 Kbps circuit switched data, X.25 packet switched data, and frame relay data.
bit— A bit (binary digit) is a basic unit of information used in computing and other digital electronics. It can take a value of either 1 or 0, represented in a computer by a high or low electrical charge.
BONDING (Bandwidth on Demand Interoperability Group)— An inverse multiplexing method that combines multiple ISDN channels into a single channel for enhanced throughput. Trademark of the BONDING Consortium.
BONDING mode 1—An industry-standard ISDN B channel aggregation protocol that was developed by the Bandwidth On Demand Interoperability Group. This mode supports user data rates that are multiples of the bearer rate. It provides the full available bandwidth, but no in-band monitoring. Mode 1 is common to all implementations of BONDING; Modes 0, 2, and 3 are optional.
BONDING Consortium—A group that develops specifications for common control and synchronization for management of high-speed data over the public network.
BONDING Specification 1.0— The Version 1.0 BONDING specification (August 1992) defines four modes of inverse multiplexing interoperability. It allows devices from various manufacturers to subdivide a wideband signal into 64 Kbps or 56 Kbps channels, and then pass the individual channels over a switched digital network, recombining them into a single high-speed signal at the receiving device.
