The rate at the time of the last
adslAtucRateChangeTrap event. It is also set at
initialization to prevent a trap being sent.
Rate changes less than adslAtucThresh(*)RateDown
or less than adslAtucThresh(*)RateUp will not
cause a trap or cause this object to change.
(*) == Fast or Interleave.
See AdslLineAlarmConfProfileEntry.