This sets the ingress buffer fill level at which the card declares a threshold-crossing alert for buffer overflow risk. Setting this too high delays warning until the buffer is nearly already overflowing, leaving little time to react before actual cell loss begins, while setting it too low generates alerts during normal traffic bursts that never actually threatened overflow, so an admin tunes it against this card's typical burst profile. For example, an admin raises this threshold after finding normal daily traffic bursts were triggering nuisance alerts well below the point where cells were actually being discarded.