Glossary

more than one bit is represented by a single cycle of the carrier.

BRI (basic rate interface)—Also called 2B+D. One of two forms of ISDN service. BRI provides two 64 Kbps B-channels for video, voice or data, and one 16 Kbps D-channel for control information. The total BRI data rate is 192 Kbps, with 144 Kbps available to the user. See also ISDN and PRI.

buffer—A temporary storage register or random access memory (RAM), used in all aspects of data communications, that prevents data from being lost due to differences in transmission speed. Keyboards, serial ports, muxes and printers are a few examples of devices that contain buffers.

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).

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.

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 equipment).

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.

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-channeland 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 implemented.

circuit-switched network—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

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

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