Subject: RE: [Sip] updated GRUU spec - routing via home domain

From: <[email-masked]>
Date: Mon, 28 Aug 2006 10:46:16 +0300

Hi,

I have not been following up the GRUU related discussions or read
the older GRUU draft. Last week I however studied draft-ietf-sip-gruu-10
and met with a paragraph which I was not unfortunately able to
understand:

   In addition, if the UA is making use of an outbound proxy, the GRUU
   that is used by the UA MUST be one obtained from a domain that will
   be visited by the request prior to being routed towards the target in
   the Request-URI.  A request can visit multiple domains if, in
   addition to an outbound proxy, a UA asks that a request visit
   additional proxies, identified by additional Route header fields in
   the request.  This can happen when a UA has learned a service route
   using the mechanisms in RFC 3608 [27].  When using a service route,
   this requirement (that the GRUU be obtained from a domain that will
   be visited by the request) it is sufficient to use the GRUU learned
   in the same registration that delivered the service route.  If there
   is no service route, and the request will visit only the single
   specified outbound proxy, the UA needs to make sure that the GRUU it
   used was obtained from the same domain as the outbound proxy.

It was especially the last statement which I did not understand at all,
and would kindly ask it to be rephrashed:

   Barring dynamic mechanisms to discover an outbound proxy, such a
   relationship needs to be configured into the UA.

But anyway what is the rationale behind this whole paragraph:

- Would routing towards such a GRUU for some reason fail if the request
  did not visit the domain from which the GRUU was obtained ? If yes,
  why ? 

- Or is it just an optimization to avoid the dialog to be routed at
  first to the outbound proxy which finally resolves the GRUU, just
  to find out that the request must for its final delivery be forwarded 
  to the domain from which the GRUU was obtained ?

I found that the paragraph has been added into the latest version 10
of gruu draft:

>* noted that, in the outbound direction, if the home proxy is not on
>the original request path, another proxy in that domain needs 
>to put in 
>a record-route
>that points to it. Provide links to some mechanism which allows a home
>proxy to get on the outbound request path
>
>* clarified that, if an outbound proxy is used, the request has to
>   visit the domain from which the gruu was obtained before being
>   forwarded to the party in the r-uri. There are two ways documented
>   to know this:
>
>    a. using a service route obtained from the same proxy that sent you
>    a gruu
>
>    b. using an outbound proxy; configuration tells you what domain its
>    from

However I was not able to find the related discussions or any rationale
or examples to justify it. Please provide clarifications to me, if you
can. A link to the corresponding discussion on the mailing list would
also do.

Regards,

Erkki
____________________________________

  Erkki Koivusalo
  Nokia Mobile Software
  tel:+358 40 7571197
  mailto:[email-masked]
____________________________________ 

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