Black Box 5000 manual Glossary

Multiserver 5000

Glossary

ABR, autobaud rate detection — A process by which a receiving device determines the data rate, code level, and stop bits of incoming data by examining the first character received (usually a preselected sign-on character). ABR allows a receiving device to accept data from a variety of transmitting devices operating at different data rates, which means that the receiver does not need to be configured for each specific data rate in advance.

ACK, acknowledgment — A control character used as a reply in communications protocols. For example, in the Hewlett-Packard ENQ/ACK protocol, ACK is sent by the receiving device as a reply to ENQ sent by the transmitting device.

ADB, automatic dial backup — A modem feature that enables it to automatically switch data transmission from the leased lines to dial lines when line impairments on the leased lines reach an unacceptable level. The modem also returns to leased-line operation when the conditions of those lines improve.

aggregate input rate — The sum of all data rates of terminals and computer ports connected to a multiplexer. “Burst aggregate input rate” is the instantaneous maximum data input rate accepted by the multiplexer.

analog — Continuously variable as opposed to discretely variable. Physical quantities, such as temperatures, are continuously variable and are described as analog; analog signals vary in accordance with the physical quantities they represent. The public telephone network was designed to transmit voice in analog form.

analog loopback — A diagnostic test that forms the loop at the modem’s telephone line interface.

answer tone — A signal sent by the called modem (the answer modem) to the calling modem (the originate modem) on public telephone networks that indicates the called modem’s readiness to accept data.

answer tone frequency — The frequency (cycles per second) of the answer tone.

APV, Advanced Packetized Voice — Low Bit Rate Voice (LBRV) digitizing technique that produces acceptable-quality voice signals and requires a bandwidth of only 9.6 Kbps.

ARQ, automatic request for retransmission — An error-control method in which the receiving device informs the transmitting device which transmission blocks were received successfully. The transmitting device retransmits any blocks not successfully received.

ASCII, American Standard Code for Information

Interchange — A 7-bit-plus-parity character set or code established by the American National Standards Institute (ANSI) to achieve compatibility between data services.

async — Short for asynchronous. See asynchronous transmission.

asynchronous transmission — A method of sending data in which the interval between characters may be of unequal length. The characters transmitted include a start bit and one or more stop bits, which define the beginning and ending of the character. No synchronizing or timing signals need to be sent.

attenuation — Deterioration of signal strength as it passes through a transmission medium; generally attenuation increases with both frequency and cable length. Attenuation is measured in terms of decibels.

bar graph — A visual indication of the input signal level strength in dB, as displayed on the command port or by the four red indicators on the voice/fax channel.

baud — A unit of signalling speed. The speed in baud is the number of discrete conditions or signal events per second. If each signal event represents one bit, the baud rate is the same as bps. If each signal event represents more than

252