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The Folly of Peering Ratios

  • From: William B. Norton
  • Date: Wed Nov 02 14:05:02 2005
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Hi all -

At the Peering BOF X at NANOG 35 in Los Angeles last week we held a
debate on the rationality of Peering Traffic Ratios as a Peering
Partner selection criteria. During the debate both sides made good
points, but interestingly, some of the strongest arguments on both
sides of the debate came out during the Q&A and during coffee
break/bar/beer-n-gear ad hoc debates that followed.  I have classified
roughly six arguments culled from these discussion, attributed where I
remembered the source, along with the corresponding counter arguments
that seemed to collectively reveal the folly of peering traffic ratios
as a peering discriminator. I have documented and diagrammed these
arguments in the form of a white paper titled, of course, "The Folly
of Peering Traffic Ratios."

I am looking for some people to review the paper, provide feedback,
better defend an argument on either side, provide anecdotes, whatever
you believe would help make the paper an accurate portrayal of the
arguments on both sides of this issue. If you have the time to let me
walk you through the paper over the phone (about 20 minutes) and
discuss, that would be the best - I find I get the most feedback this
way. I'll send out a note to the list when I have done enough walk
throughs to feel comfortable enough that I have things about right and
that the draft can be circulated more broadly.

Here is the current summary from The Folly of Peering Ratios v0.5:
------------------------------------------ snip
In the heated discussions surrounding this topic there were six
flavors of arguments put forth to support peering traffic ratios as a
peering selection criteria.

Argument #1 - "I don't want to haul your content all over the world
for free." This argument is countered with the observation that,
whether peered with a content heavy or an access heavy ISP, the ISP is
being paid by its customers for providing access to that traffic. It
is not hauling the traffic for free.

Argument #2 – "OK, but there is massive asymmetry here. Look at how
many bits miles I have to carry your content, while you have only to
deliver your content across the exchange point." Regardless of whether
peered with content or access the load on your network is about the
same; the access or content traffic has to traverse your network to
get to your customers. This is an argument perhaps for more
geographically distributed points of interconnection.

Argument #3 – "As an Access Heavy ISP, I don't want to peer with
Content Heavy ISPs, because doing so will screw up my peering traffic
ratios with my other peers."  The analysis and diagrammed traffic
flows in this paper prove this assertion true, however, the argument
is circular: 'Peering Traffic Ratios are valid criteria because they
support Peering Traffic Ratios with others.'

Argument #4 – "I want revenue for carrying your packets." While this
argument is business rational, peering traffic ratios are a poor
indicator of the value derived from the interconnection.

Argument #5 – "My backbone is heavily loaded in one direction – I
don't have $ to upgrade the congested part of my core without a
corresponding increase in revenue." This loading problem can better be
solved with better traffic engineering, with more resources for the
core or by temporarily postponing all additional peering until the
core is upgraded. Introducing a peering traffic ratio requirement is
at best a temporary solution and signals a poorly managed network – a
bad image for peers and transit customers alike.

Argument #6 – "I don't want to peer with anyone else. Peering ratios
help me systematically keep people out." This is an understandable
(although seldom articulated out loud) argument but is a poor defense
for peering traffic ratios per se since it is an arbitrary
discriminator; one could just as well have specified the size of the
backbone core, the market capitalization or debt structure, or an
extremely large number of distributed interconnect points.

Peering Traffic Ratios emerged years ago in the Internet as a peering
candidate discriminator, but appear to have their roots in the PSTN
world. Ratios reflect the telephony settlement model of buying and
selling minutes, where the traffic difference between in and out is
used for settling at the end of the month. However, the Peering
Traffic Ratio discriminator model for the Internet interconnection
fails because traffic ratios are a poor indicator of relative value
derived from the interconnect.

If you have time to review the paper (about 6 pages), please send me a note.


// William B. Norton <[email protected]>
// Co-Founder and Chief Technical Liaison, Equinix
// GSM Mobile: 650-315-8635
// Skype, Y!IM: williambnorton