Glossary
MTA128ST/NT 54
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).
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 b usiness
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 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
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 i n the PSTN (public switched telephone network). A
business PABX or any residential t elephone connec ts 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).
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 u sed 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 fro m
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