Re: [Sip] two questions for route information preprocessing of initial INVITE with Route headers

["Dale Worley" <dworley at nortel.com>]

On Fri, 2009-09-18 at 13:46 +0800, ding.xuexin at zte.com.cn wrote:
> Hi, all
> 
> 
> I have two questions for route information preprocessing of initial INVITE
> with Route headers
> 
> 
> first question:
> 
> UA(or B2BUA) receives an initial INVITE with Route headers, assuming UA's
> host is example.com
> 
> if the sip entity which sends the INVITE is a loose router, the INVITE may
> be like this:
> 
>    INVITE sip:bob at example.com
>    Route: <sip:xx at example.com;lr>
> 
> if the sip entity which sends the INVITE is a strict router, the INVITE may
> be like this:
> 
>    INVITE sip:xx at example.com
>    Route: <sip:bob at example.com>
> 
> we cannot distinguish those two scenarioes because Requet-URIs in two
> scenarioes are similar.
> if we do route information preprocessing according RFC3261 section 16.4, we
> will get two different
> results. And there is no desciption for UA route information preprocessing
> in RFC3261, RFC3261
> section 16.4 just describes proxy behavior.
> 
> How to processing route information of initial INVITE with Route headers
> for UA?

The first question is whether the element is prepared to act as a proxy
(as well as a UA).

If the element is not prepared to act as a proxy, it can't process the
request properly, as the semantics are "First send to <sip...>, and let
it send to <sip...>".  So it should either ignore the message or return
an error.

If the element is prepared to act as a proxy, it should process the
message as a proxy would.

Dale