Glossary
Issue 8.0 July 2002
GL-15
OSI
Open Systems Interconnection — Referring to the OSI reference model, a logical structure for net-
work operations standardized by the International Standards Organization (ISO).
OTDR
Optical Time Domain Reflectometer.
P
Parameter
A characteristic of the system that affects its operation.
Path
A path at a given rate is a logical connection between the point at which a standard frame format
for a signal at the given rate is assembled and the point at which the standard frame format for the
signal is disassembled.
Path AIS
Path Alarm Indication Signal — A path level code that is sent downstream in a digital network as
an indication that an upstream failure has been detected and alarmed by some upstream equip-
ment, if the upstream alarm has not been suppressed.
Path Terminating Equipment
Network elements in which the path overhead is terminated.
Path Trace Signal
The path trace signal is provided in the STS-1 path trace byte (J1) of the path overhead. The path
trace signal is transmitted repetitively to verify the continuity of the STS-1 path. The DS3 circuit
pack is the only low speed interface circuit pack that generates or terminates the STS-1 path over-
head.
Path Unequipped Signal
The path unequipped signal is provided in the STS-1 path signal label byte (C2) of the path over-
head. The path unequipped signal is transmitted to notify downstream equipment that the STS-1
path is incomplete (for example, a low speed interface slot in the AUTO state or the absence of a
valid cross-connection). The DS3 circuit pack is the only low speed interface circuit pack that termi-
nates the STS-1 path overhead.
Path Yellow Signal
A maintenance signal used to indicate the presence of an alarm, detected at the remote terminal, in
the path originating locally. Also, refer to the path remote defect indicator ^(RDI-P) signal.
Payload Pointer
The offset in bytes from the Pointer Action Byte (H3) to the beginning of the synchronous payload
envelope.
PC
Personal Computer.
PCN
Product Change Notification — Product change notifications are issued to notify customers that
in-service product changes are required to correct an existing or potential problem. Product change
notifications are issued through the Design Change Management System.
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