This sets the congestion-level fill threshold for the CBR queue on the switching port's Pearl ASIC, distinct from and typically lower than the corresponding overflow threshold. Because this measures sustained congestion pressure rather than an outright overflow event, an admin typically sets it below the corresponding overflow threshold so it fires as an earlier warning, giving time to react to a building CBR congestion trend before cells actually start being discarded. For example, an admin deliberately keeps this congestion threshold below the CBR overflow threshold so the congestion alert always fires first, providing lead time before real cell loss.