A desired threshold for the number of Unavailable Seconds (UAS)
within any given 15-minute performance data collection interval.
If the number of UASs in a particular 15-minute collection
interval reaches or exceeds this value, a
gBondPmTca15MinUASCrossing notification MAY be generated if
enabled by gBondPortConfPmTcaEnable.
At most one notification can be sent per interval.
Setting this attribute to zero (default) effectively disables
gBondPmTca15MinUASCrossing notification.
This object maps to the TR-159 attribute
aGroupPerfThreshold15MinUAS.