Re: [Sip] RE: Identity after reinvite

Paul Kyzivat wrote:

> By "this" I assume you mean the to-from-change option?
> 
>  > only if you assume that the problem lies in the UA; I would
> 
>> be worred about other nasties along the way.
> 
> 
> For changing on subsequent requests within the dialog, what nasties are 
> you thinking of? I think only a call stateful proxy would notice, and it 
> seems there aren't many of those. Of course there are B2BUAs, but they 
> at least *ought* to be UAs and behave as such.

Ought, being the operative word here. I fear that a b2bua would pass the 
Supported headers unmodified and then things would be bad.

>> In any case, I don't see a need for a Supported header field. The 
>> feature is supposed to work with any rfc3261 client out there.
> 
> 
> Other than just hoping for the best, why would we expect existing 3261 
> clients to work with this change?

It is explicitly called out in 12.2.1.1:

> The URI in the To field of the request MUST be set to the remote URI
>    from the dialog state.  The tag in the To header field of the request
>    MUST be set to the remote tag of the dialog ID.  The From URI of the
>    request MUST be set to the local URI from the dialog state.  The tag
>    in the From header field of the request MUST be set to the local tag
>    of the dialog ID.  If the value of the remote or local tags is null,
>    the tag parameter MUST be omitted from the To or From header fields,
>    respectively.
> 
>       Usage of the URI from the To and From fields in the original
>       request within subsequent requests is done for backwards
>       compatibility with RFC 2543, which used the URI for dialog
>       identification.  In this specification, only the tags are used for
>       dialog identification.  It is expected that mandatory reflection
>       of the original To and From URI in mid-dialog requests will be
>       deprecated in a subsequent revision of this specification.

Only the tags are ever used in any normative processing of dialogs in 
RFC 3261. The requirement to set the From field *URI* in the reverse 
direction to the value of the To URI in the original INVITE is *only* 
for backwards compatibility, and rfc3261 stated that this is likely to 
change one day. The day appears to be at hand.

-Jonathan R.
-- 
Jonathan D. Rosenberg, Ph.D.                   600 Lanidex Plaza
Director, Service Provider VoIP Architecture   Parsippany, NJ 07054-2711
Cisco Systems
jdrosen@cisco.com                              FAX:   (973) 952-5050
http://www.jdrosen.net                         PHONE: (973) 952-5000
http://www.cisco.com

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