This attribute is only valid for AtmIf's on ATM IP FPs. It is not
displayed for AtmIf's on other card types.
This attribute indicates the congestion state of the transmit cell
memory for this AtmIf. It indicates which txCellMemoryThreshold
corresponds to the current value of txCellMemoryAvailable.
The congestion state of memory is indicated by a numeric value
ranging from 0 to 3. When memory is in a congested state 'x', only
traffic with discard priority (DP) < 'x' is definitely still queued for
transmit. Traffic with DP > 'x' is definitely discarded. Traffic with
DP = 'x' may be either queued or discarded depending on how
close the value of txCellMemoryAvailable is to the next threshold as
displayed in txCellMemoryThreshold. For example, CLP1 traffic is
queued until the value indicated by txCellMemoryAvailable reaches
the DP3 threshold. At that point, the CLP1 traffic is discarded.