This Unsigned32 (0..100) is the percentage-based version of the overflow ceiling, per its DESCRIPTION -- readings within this percentage above the basis value are normal, and readings above it register an overflow condition. As with the adjustment percentage field, expressing the overflow ceiling as a percentage of the basis rather than a fixed count means the overflow detector keeps working correctly as the basis value itself is renegotiated over the port's life, without an operator having to manually recompute a fixed threshold after every capacity change. For example, a 20 percent overflow threshold on a basis that has just doubled after a bandwidth upgrade continues to trigger at the same relative excess (20 percent above whatever the new basis is) with no reconfiguration needed.