Subject: Re: [martini] draft-vanelburg-martini-friends-00

From: Paul Kyzivat <[email-masked]>
Date: Wed, 16 Jun 2010 19:35:23 -0400

Somehow I missed this draft before, but following the interim meeting 
today I read it.

IIUC this proposal is similar to the original "shaken" proposal (I think 
that was the one) to use the Contact-URI from REGISTER as a Route header 
rather than using it to rewrite the R-URI (which was adapted for martini 
by the gin draft).

There were pros and cons to both of those proposals. IMO we eventually 
decided to pursue -gin because its balance of pros to cons was thought, 
at the time, to be better than the alternative.

Now -friends essentially proposes to adopt both approaches. ISTM that is 
the worst of all possible worlds. Its double the work for those who want 
to support both, and it presents interop problems for those who don't 
support both. And its just two solutions to the same problem - there is 
almost no benefit to having both over having one.

IMO there needs to be a *choice* among alternative approaches. (They pay 
us the big bucks to make hard choices.) Potentially we could make such a 
choice, if we had two proposals of comparable completeness to choose 
among. For that I think we would need another draft, that fleshes out 
the "domain federation" approach. (Maybe -shaken or another of Hadriel's 
early drafts on the subject could be a starting point.) Just pointing to 
an ETSI document isn't enough.

Some tricky things that have come up along the way with -gin would also 
need to be dealt with in this alternative. Among them is GRUU, 
especially temporary GRUUs. Something similar to what Adam has proposed 
for -gin is probably needed to address the same issues.

Also, some issues unique to this approach need to be addressed. 
Specifically, how does the registered contact that becomes a Route 
header interact with
- existing Route headers in the incoming request?
- Path headers that were registered?

There may also be issues with routing spirals when using GRUUs. This was 
a knotty problem in IMS. (I wrote some text regarding that which may or 
may not have made it into 24.229.) (To be fair, this issue may also 
exist with -gin, so it will need to be investigated/solved either way.)

I liked Jonathan's original proposal to switch registration routing to 
use Route headers. I could be happy with a Martini approach that went in 
that direction if it deals with all the loose ends.

So to the authors of -friends (and their friends) I suggest that if you 
want to see a martini solution that uses the "domain federation" 
approach, please submit a draft that spells out all the details needed 
to define that.

	Thanks,
	Paul