Subject: [Speermint] Some words on the federation concept

From: Otmar Lendl <[email-masked]>
Date: Thu, 13 Mar 2008 17:45:37 +0100

At yesterday's session, someone (I forgot, who) voiced his suspicion
that everybody has his own view of what a federation is and what not.

We need to clear that up to make progress.

Here is my PoV:

The definition (from terminology-16) is:

  A federation is a group of SSPs which agree to receive calls from
  each other via SIP, and who agree on a set of administrative rules for
  such calls (settlement, abuse-handling, ...) and the specific rules
  for the technical details of the peering.

(this is basically unchanged from
http://www.enum.at/ietf/draft-lendl-sip-peering-policy-00.txt 
of december '05)

My motivation for this definition was the following idea:

* The numbers of SSPs worldwide could be in the same order as the number
  of mailservers in the Internet. This is a huge number.

* As I don't assume that every possible pair of two SSP will peer with
  each other, we will need some sort of transit routing.

* To make that manageable, the number of routes needs to come
  down. We need an aggregation step.

* Thus federations: If reaching a federation equals having a 
  path to all members of this federation, then we can base the
  call routing on federation IDs, and not on SSPs

  Only within a federation, routing is towards a specific SSP.

This is in analogy to layer 3 routing. The routing table contains
routes to subnets. Once a router notices that it has an interface
within the same subnet as the destination address of the IP
packet it needs to route, then the IP routing layer has done
its job and packet routing is passed to whatever L2 network
implements this shared subnet.

Translated to federation based VoIP routing, this means that
once a source SSP detects that he shares a common federation
with the destination SSP, then the high-level routing algorithm
is finished and a federation-specific one starts.

All this (just as for IP routing) works only if every SSP in a
federation talks to every other SSP in this federation.

------

Second point: A federation is per definition not more than a
mathematical set of SSPs. This set of SSPs might have decided that
they need some sort of federation infrastructure, be it a common L2
network, a X.509 CA, an ENUM tree, or a central SIP proxy. Of course, a
federation can be run by a commercial entity.

But it's not needed. The set of all SSPs implementing RFC 3263 on the
public Internet is by definition a federation. (as mentioned during the
session, this the purest form of an on-demand peering)
Just as well is a private peering between two SSP a federation.
(probably the most extreme case of a static one)

The 10000 feet view of the overall call routing scheme does not care.
Just look at the words of the definition.

(The same applies btw to IP routing: a subnet can be a point-to-point
link just as well as a X.25 or ISDN on demand dialing network spanning
thousands of hosts. The L3 routing algorithm doesn't care a jota.)

------

It is certainly worthwhile to consider peering fabrics where not all
members peer with each other (just as on IP Exchange Points).

That, too, is a useful concept. But it's not a federation according to
the definition in terminology-16.

/ol
-- 
// Otmar Lendl <[email-masked]>, T: +43 1 5056416 - 33, F: - 933
// nic.at Internet Verwaltungs- und Betriebsgesellschaft m.b.H
// http://www.nic.at/  LG Salzburg, FN 172568b, Sitz: Salzburg
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