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Glossary
Issue 5 June 2000 GL-15
P
PC
Personal Computer.
PID
Program Identification.
PINFET
Positive Intrinsic Negative Field Effect Transistor.
PJC
Pointer Justification Count.
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 different at
any particular instant. For example in SONET networks, each timing traceable 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 degrading 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 initiate
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 normally carrying traffic. (See "Ser-
vice Line.")
PRM
Performance Report Message.
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