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Reader
Questions
Following
are some of the questions we have received from
our readers:
Question:
What is a Carrier Group Alarm (CGA)?
Answer: Telcordia
Specification GR-303 defines a Carrier Group Alarm (CGA)
as the combination of a Carrier Failure Alarm (CFA)
and Trunk Conditioning (TC).
The CFA is the detection of a continuous Loss
of Signal (LOS) or Out Of Frame (OOF) defect on
an interface. The LOS or OOF defect must be
present for a time "X" where X is in the range from
2 seconds to 3 seconds. The CFA corresponds to
the ANSI T1.231 specification of the Loss of Signal
failure or the Out
Of Frame failure.
Trunk Conditioning (TC) is the application of algorithms
that will prevent false billing, remove affected voice
channels from service and implement a coordinated service
restoral mechanism once the failure is cleared.
Question:
What are RED, BLUE and YELLOW alarms?
Answer: Historically,
colors were used to signify types of alarms for
T1 and T3. However, the use of color descriptions
have been depreciated in favor of more descriptive
failures: Loss of Signal (LOS) failure, Out Of
Frame (OOF) failure, Alarm Indication Signal (AIS)
failure, and Remote Alarm Indication (RAI) failure. Failures
in this context are the same as alarms and are defined
in ANSI T1.231.
Defects differ from alarms as a defect is a momentary
impairment on the interface. Defects are integrated
over time until they are declared failures. For
example, a LOS failure is the detection of the LOS
defect, integrated over time until a LOS failure is
declared. The typical LOS failure integration
time is 2.5 seconds.
RED - A red alarm is the combination of an LOS OR
an OOF failure. In this way, RED can be used
as part of the CGA as described in the first question.
BLUE - A blue alarm is the AIS Failure. Typically,
an AIS signal is transmitted on a line when an interface
is operational, but unable to offer service. AIS
may also be inserted by multiplex equipment to indicate
when failures in the multiplexer are preventing valid
signals from being generated.
YELLOW - A yellow alarm is the RAI failure. An
RAI is sent to the far end equipment to indicate that
there is a problem receiving the far end's signal. An
RAI is sent when the near end detects an LOS, OOF or
AIS failure.
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