ADTRAN 1200270L1, Manual

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Appendix F. Glossary
61200270L1-20 DSU III ARdc User Manual F-7
start bit
In asynchronous data communications, characters are sent at arbi-
trary intervals. In order for the computer to make sense of what is
coming in, each character starts its transmission with a start bit. This
way if the first bit of the character to be transmitted is a 0, the fact of
receiving a start bit (always a 1) tips off the computer that the next bit
is part of a transmitted character and not just part of the inter-charac-
ter gap. See stop bit.
stop bit
The stop bit is an interval at the end of each asynchronous character
that allows the receiving computer to pause before the start of the
next character. The stop bit is always a 0. See start bit.
switched
In regard to DSU/CSUs, the ability to perform the functions of estab-
lishing and releasing connections on a per call basis between two or
more circuits, services, or communications systems. The DSU III S2W
and DSU III S4W are examples of Switched 56 DSU/CSUs.
synchronous
Communications in which the timing is achieved by sharing a single
clock. Each end of the transmission synchronizes itself with the use
of clocks and information sent along with the transmitted data.
tail circuit
A feeder circuit, which may be digital or analog, that provides an
access line to a digital or analog network.
UL
Underwriters Laboratories. A laboratory established by the National
Board of Fire Underwriters that tests equipment, materials, and sys-
tems that may affect insurance risks, with special reference to fire
dangers and other hazards to life.
V.25 bis
Automatic calling and answering command set including the ability
to work with async, bisync, and HDLC devices. Provides a small
subset of the functions of the Hayes Standard AT Command Set.