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Re: C&W Peering Problem?

  • From: Leo Bicknell
  • Date: Sat Jun 02 14:27:36 2001

On Fri, Jun 01, 2001 at 07:28:03PM -0700, Sean Donelan wrote:
> So, can anyone explain why C&W, UUNET or Genuity care about traffic
> balance, other than to limit competition by providers who are better
> at attracting particular types of customers than them?  If you are good
> at being a webhoster, your traffic will have one profile.  If you are
> good at being an access provider, your traffic will have another profile.

There are several reasons to care about traffic ratio.  Where I
think the mistake is made is that providers are looking at ratio,
but that the ratios they use are fixed regardless of the type of
network they are evaluating.  That said, it's hard to get more
flexable guidelines past the lawyers and bean counters, particularly
in a large orginization.

Here's a few interesting cases, first, the ratio problem.

         A1--------------B1---User
         |                |
         |                |
         |                |
server---A2--------------B2

Consider "A" is west coast, "B" is east coast.  User requests flow
B1, B2, A2, while reponses flow A2, A1, B1.  Provider 1 ends up
carrying more bits a longer distance, and thus incurs a higher
cost.

There are several responses to this argument, each with their own
problems:

* That's what you get for building and end user network.  If you
  don't like it, build a data center network.  Most people don't
  like suggesting their business model is broken.

* Use BGP MEDs to make the return route A2, B2, B1.  This moves
  the cost to network 2, which may or may not be fair.  Many times
  provider 1 does not trust provider 2 to do this properly. Even
  when they do, sometimes it is impossible.  BBN and ATT are good
  examples.  If someone sends you a single /8, you have no choice
  but to hot potato it out, as meds make no sense.  The only solution
  is deaggregation, which has a large number of other problems.

* A settlement should be paid from network 2 to network 1.  This
  is possibly acceptable, if it comes in the form of a settlement.
  Often the pricing resembles transit, below.

* Network 2 should buy transit from network 1.  Most of the medium
  to large networks are trying to be transit free, and reject this
  outright.  Also, it's quite likely they would by transit from,
  well, anyone else just so network 1 doesn't get the money from it.

There is an important factor here many of the depeering crowd are
missing.  The overall traffic ratio of your network is more or less
fixed, and is determined by your customer base.  Unless you can
convert peers to customers (which I have never seen someone be
successful in doing on any scale), you will simply move the problem
around.  That is, if you're 2:1 with Sprint, and depeer 5 10:1
guys, they may well buy transit from Sprint, moving them to 3:1
(due to traffic volume).  Now what, depeer Sprint?

Most people from their billing software can add up all customer in
and all customer out.  If your ratio is under that number, you will
_NEVER_ reach it, no matter what you do.  Since individual peers
will be different, you probably want your limit to be about twice
your customer ratio, at a minimum.

This is why I believe you have to evaulate people based on value.
Consider someone like @home peering with someone like Globix.  One
is a pure end user provider, that in fact prevents most of it's 
users from running servers and the like.  The other is a pure web
hosting company, with lots of content and almost no users.

These two networks _cannot exist without each other_.  If they
refused to peer with each other based on ratio, it would be utter
folly.  Clearly there is great value to both of them in peering,
even though the ratio may well be 10:1 or higher.

One of the funniest results of the ratio dance is that it may well
create more competitiors for a large network.  A tight ratio (eg,
1.5:1) is really a requirement that you have a similar customer
mix, so you have a similar amount of in+out traffic.  How many web
hosting networks, who didn't want to compete for end users have
been forced to go after end users big time?  How many access only
networks have done things to attract server users?  Companies that
could have enjoyed much less competition have forced people to
compete with them by ratio.

Equally interesting to me is the "minimum traffic" numbers that
many large networks want to put forth.  Some of them are quite
high, with major networks requiring well over a gig of actual
traffic to qualify for peering.  This has the effect of pushing
the restrictive peering policies down to smaller providers.  If a
smaller provider has a lot of peers, they send less traffic to any
individual peer.  One of the easiest ways to get that traffic level
is to pull peering with a bunch of transit customers of the network
you need to increase traffic with, which of course increases your
reliance on that paritcular peer.

One could wonder if some large providers pushed C&W due to the
lack of traffic between their networks (since we know C&W had some
issues where they couldn't grow their network last year, and had
trouble turning up new customers) and that wasn't one of the 
catalysts for this most recent action.

-- 
Leo Bicknell - bicknell@ufp.org
Systems Engineer - Internetworking Engineer - CCIE 3440
Read TMBG List - tmbg-list-request@tmbg.org, www.tmbg.org




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