How quickly they forget.

UUNet bills for the MAXIMIUM 95th percentile on inbound OR outbound, whichever is higher, as does AboveNet, and probably the majority of networks trying to be like UUNet.

In case this is unclear, AboveNet was the first to do 95th percentile, and UUNet was the first of those who have since followed in Dave Rand's footsteps.

But a significant portion of other networks will bill for the AVERAGE under the 95th percentile.

When I asked DLR why he those 95th percentile he claimed it was to account for the "averaged peak load" that a customer put on his backbone. Throwing away the highest 5% of samples was somewhat arbitrary -- could have been 4% or 6% and the result would've been about the same. What he was trying to get at was a way to make what the customer paid be related to what it cost him to provision backbone and peering links. It seems, based on the rest of the industry having followed his example, that he was onto something.