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