ADTRAN DSU III TDM Manual page 128

Appendix F. Glossary
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.
TDM
time division multiplexing. A method for sending two or more signals over a
common transmission path by assigning the path sequentially to each signal,
each assignment being for a discrete time interval.
U interface
A twisted-pair subscriber loop carrying an ISDN 160 kbps digital signal
between the ISDN central office and the NT1 at the customer premises.
UL
Underwriters Laboratories. A laboratory established by the National Board
of Fire Underwriters that tests equipment, materials, and systems that may
affect insurance risks, with special reference to fire dangers and other haz-
ards to life.
UL 1459
A UL rating that assures the connected equipment (DSU/CSU) provides pro-
tection from current overloads and power line crosses.
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 func-
tions of the Hayes Standard AT Command Set.
V.32 bis
Higher speed CCITT standard for full-duplex transmission on two-wire
leased and dial-up lines at 4.8, 7.2, 9.6, 1.2, and 14.4 kbps. They do not rely
on compression to achieve that high speed.
F-8 DSU III TDM User Manual 61200063L1-20