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FW: Private and Public Peering
From: Lane Patterson <lpatterson () equinix com>
Date: Mon, 19 Jun 2000 18:05:43 -0700

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

        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

- 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.


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

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