-----Original Message-----
From: Jonathan Rosenberg [mailto:jdrosen at cisco.com]
Sent: Wednesday, September 27, 2006 9:53 PM
To: jbemmel at zonnet.nl
Cc: IETF SIP List
Subject: Re: [Sip] GRUU and Grid alternative
jbemmel at zonnet.nl 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
jdrosen at cisco.com FAX: (973) 952-5050
http://www.jdrosen.net PHONE: (973) 952-5000
http://www.cisco.com
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