This object is the number of distinct congestion levels, from zero to four, this specific association's implementation supports. This tells the admin how granular the congestion-control thresholds configured through the abate and onset objects below actually are for this one link; a value of zero means no tiered congestion control is in effect at all, while several levels provide graduated backoff. A value of 3 means this association can distinguish three separate congestion severities, each with its own onset and abate threshold, rather than treating any congestion the same way.