Black Box 5000 manual 255

CPU, central processing unit — The heart (main processor) of a computer system, or the computer system itself.

<cr>, carriage return — A user-entered ASCII or EBCDIC control character used to position the print mechanism of a printer, or the cursor on a terminal display, at the left margin.

CRC, cyclic redundancy check — An error- detection scheme in which the block-check character is the remainder after dividing all the serialized bits in a transmission block by a predetermined binary number. Also, a polynomial based on the data transmitted.

CSA — A Canadian government agency that generates standards, conducts tests, and certifies products to ensure their safety.

CSU, channel service unit — A digital DCE unit for DDS lines; interfaces with DSU on customer’s premises.

CTS, clear-to-send— An RS-232 interface control signal which indicates to a DTE that it may begin transmitting. Usually issued in response to RTS.

data — Numbers, text, facts, instructions, and the like, represented in a formalized manner that can be manipulated and transmitted by machines.

data compression — A primary technology built into the Multiserver products. A block of data is compressed for transmission and decompressed upon reception. Fewer bytes are required for the transfer, thus increasing the data transfer rate.

data pump — The heart of the modem; its functions include digital-to-analog and analog- to-digital conversion, modulation and demodulation, and interfacing to the digital and VF lines.

data rate or data signaling rate — A measure of how quickly data is transmitted. It is best expressed in bps. It is, however, often incorrectly expressed in baud. Data rate is synonymous with speed.

Glossary

dB, decibel — A comparative (logarithmic) measure of signal power.

dBm — An absolute measure of signal power, where 0 dBm is equal to one milliwatt into 600 ohms.

DCE, data communications equipment — The equipment that provides the functions required to establish, maintain, and terminate a connection (including signal conversion) for communications between a DTE and a telephone line or data circuit. Also, interface signals typically presented by this equipment.

DC signaling — A configurable signaling option in an E&M-strapped voice/fax channel. When so configured, the channel senses the idle/active status by the DC condition of the M-lead, and indicates the idle/active status to the remote end by the DC condition on the E-lead.

DDS, dataphone digital services — A communications service offered by the telephone company to transmit data in digital form.

decadic pulsing — See pulse dialing.

dial-up line, dial line — A circuit or connection on the public telephone network.

DID, direct inward dialing — A service offered by the telephone company allowing an outside caller to dial an internal extension without passing through the operator. Billing does not start until the extension answers.

digital loopback — A diagnostic test that forms the loop at the modem’s DTE interface.

DISA, direct inward system access — A service offered by a PBX which allows incoming calls to the PBX to have dialing access within the private network. It may often be protected by a dialed password. Billing starts when the PBX provides the dial tone.

disconnect supervision — Indicates to the local user that the remote end has gone off-hook. This protocol is significant in loop start, where disconnect is denoted by removal of power to the station equipment.

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