Appendix E: Glossary
ASCII
American Standard Code for Information Exchange. Coding method used by small computers to
convert letters, numbers, punctuation marks, and other characters into digital form that can be
recognized by computers.
Call progress tones
Tone information sent from the central office to tell the caller of the progress of a call; for
example, ringback, busy, and reorder tones.
DTMF
Dual-tone multifrequency. Pushbutton telephone signaling.
LED
Light-emitting diode. A semiconductor diode that emits light when a current is passed through it.
Used for status and information displays on electronic devices.
Loop current
The DC current that flows through telephone wires when a line is off-hook.
Parity bit
A binary bit appended to a data word to make the sum of bits in every word always odd or always
even. Parity bits are checked at the sending and receiving ends as a means of detecting errors in
transmission of data.
RS-232-C
Standard developed by Electrical Industries Association () to define the type of signals and
mechanical connections used between data communication devices.
T-311
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