Glossary
Issue 3 June 2000
GL-21
U
UAS
Unavailable Seconds. In performance monitoring, the count of seconds in which a signal is declared
failed or, in which, 10 consecutively severely errored seconds (SES) occurred, until the time when
10 consecutive non-SES occur.
Unidirectional
A protection switching mode in which the system at each end of an optical span monitors both ser-
vice and protection lines and independently chooses the best signal (unless overridden by an
equipment failure or by an external request, such as a forced switch or lockout). In a system that
uses unidirectional line switching, both the
service
and
protection
lines may be
active
simulta-
neously, with one line carrying traffic in one direction and the other line carrying traffic in the other
direction. The K1 and K2 bytes in the SONET line overhead are used to convey to the far end which
line the near end receiver has chosen, so that an "active" indication may be made at the far end.
UOC
Universal Optical Connector — Receptacles on the faceplate of some OLIUs that accept ST, SC, or
FC connectors.
UPD/INIT
A pushbutton on the user panel.
V
V- DT
Virtual-Distant Terminal
VF
Voice Frequency
VLSI
Very Large Scale Integration — Refers to very complex state of the art integrated circuits.
VM
Violation Monitor — A mode of the DS3 circuit pack in which it will monitor but not remove P-bit par-
ity violations on the DS3 signal received from the fiber.
VMR
Violation, Monitor, and Removal — A mode of the DS3 circuit pack in which it will monitor and
remove P-bit parity violations on the DS3 signal received from the fiber.
V- MS DT
Virtual Multi-Services Distant Terminal
VONU
Virtual Optical Network Unit
VT
Virtual Tributary — A structure designed for transport and switching of a sub-DS3 payload.
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