GL-20 Issue 5 June 2000
363-206-208
Glossary
TSA
Time Slot Assignment.
TSI
Time Slot Interchange.
U
UAS
Unavailable Seconds. In performance monitoring, the count of seconds (1) in which a
signal is declared failed or, (2) 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 moni-
tors both service 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
simultaneously, 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.
UPD/INIT
A pushbutton on the user panel.
V
VF
Voice Frequency
VLSI
Very Large Scale Integration — Refers to very complex state of the art integrated cir-
cuits.
VM
Violation Monitor — A mode of the DS3 circuit pack in which it will monitor but not
remove P-bit parity 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 moni-
tor and remove P-bit parity violations on the DS3 signal received from the fiber.
VT
Virtual Tributary — A structure designed for transport and switching of a sub DS3 pay-
load.
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