From traffic engineering point of view, I suspect the direct circuit interconnection, private peering model to be considerably simpler to deal with than the exchanged based model.
In the direct circuit case, if the interconnect pipe does not have the umph to satisfy the performance characteristics of the peering traffic, it can be relatively easily detected (percentage of packet loss) and resolved between the two parties (buy more or fatter pipe). In the exchange case, assuming the exchange box is connecting an OC12 link from each of 4 providers. If provider A is experiencing problem with provider D, it could be due to the problem with the pipe and other stuff associated with provider D, but just as likely, it may be due to having too much concurrent traffic from provider B and C with D. Such overloading due to [temporal] traffic aggregation can be pretty tricky to identify [particularly provider A will unlikely to have access to traffic profile/log of provide B and C] and even tricker to figure out what to do. Regards, John leong -- --------------------------------------------------------- Bell Labs Research johnleong@research.bell-labs.com 4995 Patrick Henry Dr. Tel: 408-567-4459 Santa Clara, CA 95054 Fax: 408-567-4448