A count of Unavailable Seconds (UAS) on the GBS since the BTU
was last restarted.
An Unavailable Second for a G.998.x interface is defined as a
count of 1-second intervals during which the bonded link is
unavailable. The G.998.x link becomes unavailable at the onset
of 10 contiguous SESs. The 10 SESs are included in the
unavailable time. Once unavailable, the G.998.x line becomes
available at the onset of 10 contiguous seconds with no SESs.
The 10 seconds with no SESs are excluded from unavailable time.
This object maps to the TR-159 attribute aGroupPerfUAS.