GL-16
Issue 9 October 1998
363-206-204
GLOSSARY
Plesiochronous Network
A network that contains multiple subnetworks, each internally synchronous and all
operating at the same nominal frequency, but whose timing may be slightly differ-
ent at any particular instant. For example in SONET networks, each timing trace-
able to their own Stratum 1 clock are considered plesiochronous with respect to
each other.
PLL
Phased-Locked Loop.
PM
Performance Monitoring — Measures the quality of service and identifies degrad-
ing or marginally operating systems (before an alarm would be generated).
PMN
Power Minor Alarm.
Proactive Maintenance
Refers to the process of detecting degrading conditions not severe enough to ini-
tiate protection switching or alarming, but indicative of an impending signal failure
or signal degrade defect (for example, performance monitoring).
POH
Path Overhead.
POTS
Plain Old Telephone Service
Protection Line
As defined by the SONET standard, the protection line is the pair of fibers (one
transmit and one receive) that carry the SONET APS channel (K1 and K2 bytes in
the SONET line overhead). On a DDM-2000 OC-3 system, a
protection
line is a
pair of fibers that terminate on an OLIU circuit pack in the
main-2, fn-a-2,
fn-b-2,
or
fn-c-2
slot. This pair of fibers serves as backup for the pair nor-
mally carrying traffic. (See "Service Line.")
PRM
Performance Report Message.
PROTN
Protection.
PRS
Primary Reference Source.
PVC
Permanent Virtual Circuit. (X.25)
PWR
Power.
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