bus—A common channel between hardware devices, either internally between components in a computer, or externally between stations in a communications network.
byte—A unit of information consisting of eight binary digits (bits). A byte holds the equivalent of a single or character (such as the letter A).
C
Call Bumping—TA feature that reallocates the second B-channel to an analog port when both B-channels are in use. If you are performing a data transfer using both channels and need to make a phone call, one channel is dropped to handle the call and then is reestablished after it is completed. With call bumping you don’t miss any calls.
call setup time—The time to establish a circuit-switched call between two points. Includes dialing, wait time, and central office– long distance service movement time.
carrier signal—An analog signal with known frequency, amplitude and phase characteristics used as a transport facility for useful information. By knowing the original characteristics, a receiver can interpret any changes as modulations, and thereby recover the information.
Centrex—A multi-line service, offered by telephone companies, that provides functions and features comparable to those of a PBX for large business users. See also PBX, exchange.
channel—A data communications path between two computer devices. It can refer to a physical medium (e.g., UTP or coax), or to a specific carrier frequency. In ISDN, two types of channels are specified: transparent (user can define the service), and nontransparent (service is assigned protocols for specific network functions). ISDN channel names are designated by a single letter, from A through M, sometimes combined with a number (see B- channel and D-channel).
CHAP(Challenge Handshake Authentication Protocol)—Security method used to verify the identity of a person or process.
CHAP MD5—Chap with MD5 digital signature algorithm imple- mented.
circuit-switchednetwork—A technology used by the PSTN that allocates a pair of conductors for the exclusive use of one communication path. Circuit switching allows multiple conversations on one talk path only if end users multiplex signals prior to transmission.
circuit switching—The temporary connection of two or more communications channels using a fixed, non-shareable path through the network. Users have full use of the circuit until the connection is terminated.
CO (central office)—The lowest, most basic, level of switching in the PSTN (public switched telephone network). A business PABX or any residential telephone connects to the PSTN at a central office.
COM port—A serial communications port on a personal computer. Normally, there are two: COM1 and COM2.
CPE (customer premise equipment)—The generic term for data communications and/or terminal equipment that resides at the user site and is owned by the user (e.g., not telephone company equip- ment).
D
DCE (data communications equipment)—Any device that serves as the port of entry from the user equipment to a telecommunications facility. A modem is a DCE for the telephone network (PSTN) that is commonly on site at the user’s premises. Packet Switched Networks have another level of DCE that is most often located at a central
office.
D-channel—A non-ransparent digital ISDN channel that operates at 16K or
64 Kbps, used for call control signalling, along with one or more B- channels. The D (demand) channel signal can control call setup, call teardown, and invocation of Supplementary Services. Is also used for telemetry and for low-speed, low-priority packet-switched data. Contrast with B-channel.
default—A preset value or option in software packages or in hardware configuration that is used unless you specify otherwise.
device driver—Software that controls how a computer communicates with a device, such as a printer or mouse.
digital data—Information represented by descrete values or conditions (contrast analog data).
digital PBX—A private branch exchange that operates internally on digital signals. See also exchange.
digital signal— A discrete or discontinuous signal (e.g., a sequence of voltage pulses). Digital devices, such as as a series of electrical pulses that have discrete jumps rather than gradual changes.
digital transmission—A method of electronic information transmission common among computers and other digital devices. Because a digital signal may be only high or low at any given time, noise and distortion can easily be removed from digital transmissions.
digitize—To convert an analog signal to a digital signal.
DIP switch—Pronounced dip switch. A set of tiny toggle switches, built into a DIP (dual in-line package), used for setting configurable parameters on a printed circuit board.
DN (directory number)—The phone number assigned to an ISDN TA at subscription time. It is a string of up to 24 characters, consisting of the valid dialing characters (0-9, *, and #).
driver—A software module that interfaces between the operating system and a specific hardware device (e.g., color monitors, printers, hard disks, etc.). Also known as a device driver.
DTE (data terminating equipment)—A term used to include any device in a network which generates, stores or displays user infor- mation. DTE is a telecommunications term that usually refers to PCs, terminals, printers, etc.
DTMF (dual-tone multifrequency)—A generic push-button concept made popular by AT&T TouchTone.
DTMF detection—A capability in some fax/data modems that can differentiate between DTMF or fax calling tones. A typical application would be a program that routes calls to specific communications applications, depending either on the type of call or on a DTMF tone added to a dialing string.
E
EEPROM (Electrically Eraseable Programmable Read-only Memory)—Upgradable memory chip often used to store firmware.
EISA (Enhanced Industry Standard Architecture)—Pronounced eesa. The purpose of the EISA bus is to provide a 32-bit bus for faster throughputs while maintaining backward compatibility with the classic ISA bus architecture.
ET (exchange termination)—The carrier’s local exchange switch. Contrast with LT (loop termination).
exchange—A unit (public or private) that can consist of one or more central offices established to serve a specified area. An exchange typically has a single rate of charges (tariffs) that has previously
