Transit Tactic 2 - Gaming the 95th Percentile

Excerpts from The Internet Peering Playbook: Connecting to the Core of the Internet

In this tactic, an ISP can (theoretically) create a $0 cost Internet Transit service by leveraging two facets of the Internet Transit pricing model discussed so far:

From these two facets, can you guess what this tactic entails?

This tactic involves “purchasing” Internet Transit from about 25 transit providers, each with a zero-commit Internet Transit service and enough capacity to carry the entire offered traffic load. The ISP running this tactic "dumps" all of its traffic for just under 36 hours to each transit provider in turn, sending zero traffic for the rest of the month to that upstream transit provider (see Figure 3-2).

Figure 3-2. Tactic 2 - Gaming the 95th percentile spreads load across 25 or so ISPs, bursting for 4% of the time and idle 96% of the time.

This tactic takes advantage of the fact that 36 hours is five percent of the month—the amount of time per month that is above the 95th percentile (where the traffic is free!). So when you look at the stack of 5-minute samples for the month, the 95th percentile measure will be zero! Starting at the 96th percentile and on up, the traffic load will be the entire offered load.

While many derivatives of this tactic have been run against Internet Transit services and bandwidth exchanges, the practitioner of this tactic must be very careful. There are several stories of ISPs using this tactic only to find that they calculated the 95th percentile measure differently than their upstream providers. The result was that multiple ISPs billed them for the full offered load! In their case, instead of paying $0, they paid double.

This tactic in its pure form is rarely seen in the Internet Peering Ecosystems anymore. Just the same, every ISP should at least understand and recognize this tactic.

The key to making this 95th percentile gaming work is the zero traffic commit and the 95th percentile billing—one of the reasons why most ISPs require minimum commits these days.



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