User`s guide

Glossary G-11
U
UA1 (Unframed All 1s)ÑWhen the DSU loses its signal from the DTE device,
it generates a
NET UA1 Received Alarm to the E1 network.
V
V.35ÑA CCITT standard for the trunk interface between a network access
device and a packet network. It deÞnes signaling for data rates greater than
19.2
Kbps.
V.52ÑTerminal emulation standard. CCITT standard (1976) for various loop-
back tests that can be incorporated into modems for testing the telephone cir-
cuit and isolating transmission problems. Operating modes include local and
remote digital loopback and local and remote analog loopback.
V.54ÑA CCITT standard for loop test devices in modems. It deÞnes local and
remote loopbacks.
X
X.21ÑAn interface between data terminal equipment (DTE) and data circuit-
equipment
(DCE) for synchronous operation on public data networks. Also, a
CCITT standard protocol for a circuit switching network.