Hansen, to directly answer your original question: 1. if ISP A peers with ISP B through a switch run by an exchange point operator, this is generally considered to be public peering. The same switch may be aggregating many other ISP's giving O(N^^2) peering relationships. 2. if ISP A peers with ISP B by connecting to ISP B's switch (which then may aggregate into ISP B's router), this is considered to be private peering, and scales to O(N) peering relationships for ISP B. This seems to be a more common way for ISP's to privately aggregate smaller (10 mbps, 100 mbps) peers to a switch, which can then use a GbE trunk to a router. However, I believe the question limits the answer and that we should think about operational peering interconnection as more than public vs. private: 1. Public Peering in Public Places: Peering via FDDI, ATM, Ethernet 3rd party exchange switches. Great for cost-effectively aggregating larger numbers of smaller peers (and scaling multicast trees). 2. Private Peering in Public Places: cross connects between colocated peers, ala Equinix, PAIX, ... bilateral control over fewer large flows, generally for Tier 1<->1 and Tier 1<->2. 3. Private Peering between Private Places: circuit from ISP POP A to ISP POP B. These aren't exact. There are a number of operational or technical gray areas: - POP-friendly buildings like Westin Bldg in Seattle can act as a "partly public space" via fiber pulls and cabling "meet-me" rooms - DPT/SRP peering ring is a multiaccess "public peering" fabric but generally seen as a way to interconnect a small number of private POPs on a ring (although extending a ring to a "public place" could be a variation) - 3rd party DACS (for SONET) and eventually OXC (for lambda trades) can scale/channelize large numbers of private cross connects. Is this a form of private peering, or public? This may depend on operational, business, and technical definitions, but it's probably a mix of 1. and 2. Cheers, -Lane

From: Scott Marcus [mailto:smarcus@genuity.com] Sent: Monday, June 19, 2000 5:46 AM

At 21:42 06/18/2000 -0700, Steve Feldman wrote:

...

The closest to a real distinction that I've been able to come up with is whether or not a third party is involved *and* whether packets (or cells) are switched.

For example, peering through a FDDI, Ethernet, or ATM switch is always called "public" (unless perhaps the switch is owned by one of the peers). And peering through a wire or SONET/SDH circuit seems to always be called private, even though the data might pass through SONET/SDH multiplexers, cross-connects, and switches operated by a third party...

Steve, this happens to be true in most cases, but I would view it as being sort of coincidental.

What most people term "public peering" is effected at a public traffic interchange point, where many providers appear, or can choose to appear. Note that the decision whether to interconnect is still, in almost all cases, a bilateral business decision between each pair of providers. The word "public" is thus something of a misnomer.

It's usually implemented over FDDI, ATM, whatever, because the traffic interchange point needs to implement any-to-any connectivity. That's a matter of engineering practicality, but the definition should not rest on it.

What most people mean by "private peering" is a direct interconnection between two providers. That's most often implemented over a circuit between the two, without either deploying equipment to the other's premises; again, however, that's simply a matter of engineering convenience. These connections are conceptually point-to-point.

Hope this was helpful, - Scott