In the past we have considered the initiator of IP transactions to be irrelevant and had no-charge peering for networks that basically send a similar number of bytes to what they receive.
Historically, customers chose backbone networks based either on geographic area or political convenience, but not the type of traffic they generated. As a result, traffic at peering points tended to even out since everyone had a mix of customer types.
So what do we do when that is no longer the case?
It's pretty clear to me that you figure out whose customers are most eager to get to what resources, and you set the price accordingly. In the BBN/Exodus case, BBN has a bunch of dialup customers who want access to Exodus' web site, and Exodus has a bunch of advertisers who want access to BBN's dialup users. At this point I'd guess that BBN's dialup users would be more upset at losing Exodus' well-known web sites than Exodus' advertisers would be at losing BBN's random dialup users, but I could imagine that it could go either way. Lest anyone think this "pay for value" approach is too complex to be used in the real world, consider the relationship between your local CATV provider and its programming sources. The provider pays for HBO, takes local broadcast for free, and gets paid for infomercial channels. -- John R. Levine, IECC, POB 727, Trumansburg NY 14886 +1 607 387 6869 johnl@iecc.com, Village Trustee and Sewer Commissioner, http://iecc.com/johnl, Member, Provisional board, Coalition Against Unsolicited Commercial E-mail