This attribute indicates the total number of one second intervals for
which the STS/STM path is unavailable. The path becomes
unavailable at the onset of 10 consecutive PSESs. The 10 PSESs are
included in the unavailable time. Once unavailable, the path
becomes available at the onset of 10 contiguous seconds with no
PSES. The 10 seconds with no PSES are excluded from the
unavailable time. For second intervals where a Path Unavailable
Second (PUAS) is counted, counting of PCV, PES, PSES and PALS
is inhibited.