BBN/GTEI

Mon Aug 24 08:48:33 UTC 1998

On Sat, 22 Aug 1998, Michael Dillon wrote:
> The users and the web servers are largely irrelevant background noise
> in this discussion of peering relationships.

They are the customers who pay backbone operators for transit.  I don't
think that that's irreleavnt.

Suppose that networks P and Q peer with each other at an exchange point
X, and network P has a customer A, while network Q has a customer
B.  Traffic flows beteen A and B, in both directions (along the paths
A-P-X-Q-B and B-Q-X-P-A), but the traffic from A to B is much more than
the traffic from B to A (and so the traffic P-X-Q is much more than the
traffic Q-X-B).  (The same argument extends trivially to asymmetric
routing through two different exchange points X and Y.)

Now, customer A is paying provider P for all the traffic in both
directions A-P-X and X-P-A, while customer B is paying provider Q for
all the traffic in both directions X-Q-B and B-Q-X.

Clearly, provider Q is paid (by its customer B) for every byte of
traffic that flows along the path P-X-Q, and for every byte that flows
along the path Q-X-P.  Similarly, provider P is paid (by its customer A)
for every byte of traffic that flows along the path P-X-Q, and for every
byte that flows along the path Q-X-P.

In this model, it makes no sense for provider P to pay provider Q, or
for Q to pay P, because each has already been paid by their respective
customers.  The cost of transit through network P (in both directions)
between customer A and exchange point X are paid by customer A, and the
cost of transit through network Q (in both directions) between customer
B and exchange point X are paid by customer B.

> Web browsing customers pay for service and web hosting customers pay
> for service. Their relationship to their network provider is a done
> deal. Once their packets enter the network they are merely packets
> full of bits that cross exchange points between peers. Forget the end
> points of the packet flows. Look at what is happening between the two
> network peers.

I believe that every packet-mile in the network operated by the web
browser's ISP was paid for by the web browser, and every packet-mile
in the network operated by the web server's ISP is paid for by the web
server.  This applies even if the number of packet miles in one ISP
greatly exceeds that in the other ISP.

--apb (Alan Barrett)