On Thu, 19 April 2001, John Hawkinson wrote:
The 5-minute average is not being sampled every five minutes.
The raw number of octets is being sampled every five minutes, and divided by the time since the previous sample (5 minutes). Then, 95th percentile is taken of that.
How do you game the system? Economists like to write a lot of papers on this subject. The problem with calculating the average is the fencepost error. Warning, majore simplifying assumptions ahead... If you transfer 1GB for exactly 5 minutes, what is your 95% bill? It depends on your timing. 00:00 Start transfer, Start measurement window 01:00 02:00 03:00 04:00 05:00 End transfer, End measurement window Elapsed time 5 minutes, total bytes 1000000, or 3,333 Bps. Bandwidth billed 3.3Kbps peak 00:00 Start measurement window #1 01:00 02:00 02:30 Start transfer #1 03:00 04:00 05:00 End measurement window #1 (500,000 Bytes, 300 Seconds) Start measurement window #2 06:00 07:00 07:30 End transfer #1 (1,000,000 Bytes, 300 Seconds) 08:00 09:00 01:00 End measurement window #2 (500,000 Bytes, 300 Seconds) Bandwidth billed 1.6Kbps peak By knowing your provider's measurement windows, you could cut your usage bill in half while transfering the same amount of data. A customer with a relatively random usage (user's surfing the web) couldn't do this, but a user transfering batch files on a set schedule may see dramatic differences in their bill. You can make the measurements more complex by using three windows, or choosing three out of five windows, and so forth. Unless providers or users are seeing real billing problems, there is little benefit to the added complexity.