Subject: RE: [Sip] GRUU and Grid alternative

From: "Michael Hammer \(mhammer\)" <[email-masked]>
Date: Thu, 28 Sep 2006 12:59:44 -0400

Jonathan,

Loose Targetting?  ;lt

Mike

> -----Original Message-----
> From: Jonathan Rosenberg (jdrosen) 
> Sent: Wednesday, September 27, 2006 10:53 PM
> To: [email-masked]
> Cc: IETF SIP List
> Subject: Re: [Sip] GRUU and Grid alternative
> 
> 
> 
> [email-masked] wrote:
> 
> > Jonathan,
> > 
> > Yes, I think this would work as a cleaner / more general 
> solution than 
> > grid
> > 
> > For the mechanism, the UA would need to insert a 'lr' 
> parameter into 
> > its Contact. This is needed for Path proxy traversal, and makes the 
> > logic at the registrar simpler (i.e. if registered contact URI 
> > contains a lr then append Route, else rewrite)
> > 
> > Perhaps 'lr' alone could be sufficient (i.e. no Supported) although 
> > you may want an option tag to detect support for this feature
> 
> Indeed. This was going to be my next post.
> 
> One of the problems with using Supported/Require in REGISTER, 
> is that it only works for proxy translation services based on 
> registrations. Other services, such as routing to a PSTN 
> gateway, or application routing, are not populated by a 
> registration. So, how would a proxy know whether to rewrite 
> the R-URI or push a Route?
> 
> The idea, as you suggest, is that if the target URI has a ;lr 
> parameter, the proxy would push a Route. Otherwise, it 
> rewrites the request uri. In this case, when a UA registers, 
> rather than using Supported/Require, it could just place a 
> URI into the Contact which contains the ;lr parameter.
> 
> This works just fine as long as you assume that existing UA 
> and routing table configurations are NOT using the ;lr 
> parameter. I got some reports that existing UA were 
> populating the Contact header field with URIs with the ;lr 
> parameter, just because they "support" loose routing (RFC 3261). 
> This behavior would break the idea of using the ;lr flag to 
> indicate this feature.
> 
> A hybrid is to use the ;lr flag just for non-register based 
> location services, and then use Supported/Require for registrations.
> 
> 
> > 
> > One difference with request URI rewriting is that the latter is 
> > automatically a one-time operation: once the URI is 
> rewritten, the proxy 
> > won't rewrite again when the request spirals. For Route 
> this is not the 
> > case. OTOH, if there are any Route headers the proxy shouldn't be 
> > rewriting / adding a route in the first place,
> 
> No. Consider the case of a Path headers. In this case, the home proxy 
> would populate the Route headers from the path set, and then 
> push the UA 
> route as the *last* Route header field. But anyway I don't understand 
> the issue you are raising with spiraling. On each spiral, a new Route 
> gets pushed. If instead you had R-URI rewriting, the only way the 
> request would get back to the proxy is if the r-uri pointed to that 
> proxy, and upon arriving there it would be rewritten again. 
> So there is 
> no difference.
> 
> -Jonathan R.
> -- 
> Jonathan D. Rosenberg, Ph.D.                   600 Lanidex Plaza
> Cisco Fellow                                   Parsippany, NJ 
> 07054-2711
> Cisco Systems
> [email-masked]                              FAX:   (973) 952-5050
> http://www.jdrosen.net                         PHONE: (973) 952-5000
> http://www.cisco.com
> 
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