The maximum period of time the SU stayed 'offline' over
the time period from the SU's first ranging message
received by HE until now.
The SU is considered as 'online' when the value for
cwdxHeSuStatusValue is any of the values: online(5),
onlineNetAccessDisabled(6), onlineKekAssigned(7), and
onlineTekAssigned(8), and the SU is considered as
'offline' for other values for cwdxHeSuStatusValue.