Subject: RE: [Sip] Issue 4 in draft-ietf-sip-connected-identity-00.txt

From: "Dan Wing" <[email-masked]>
Date: Fri, 7 Jul 2006 18:21:20 -0700

> -----Original Message-----
> From: Elwell, John [mailto:[email-masked]] 
> Sent: Tuesday, May 02, 2006 1:24 PM
> To: [email-masked]
> Subject: [Sip] Issue 4 in draft-ietf-sip-connected-identity-00.txt
> 
> The fourth issue is not actually in draft-00 but was raised
> subsequently.  If a UA supports a change of From header field URI
> mid-dialog, as indicated by the "id-change" option tag, we could
> mandate that it also support the SIP UPDATE method.  Then the peer
> UA in a dialog would be free to use the UPDATE method to report
> connected identity, rather than the less suitable re-INVITE method.
> The use of UPDATE means 2 messages instead of 3 and avoids the need
> for an offer-answer exchange.  I heard no objections when this was
> proposed a few days ago.  Do we have consensus?

I prefer UPDATE.  I am considering the needs of some proposed 
SRTP keying techniques which could benefit from strong authentication
of identity and of the fingerprints or certificates in SDP.  For
those cases it's helpful to include SDP in the UPDATE so that it
gets signed with Identity, even if that SDP is exactly the same as
the SDP in the answer.  An example of where Identity could help is 
with a pure DH mode (such as draft-baugher-mmusic-sdp-dh).  It can 
also help provide additional protection of a UA's self-signed 
certificate (various MIKEY modes) or certificate fingerprint 
(mmusic-comedia-tls, mcgrew-tls-srtp).  

Even without SRTP and without comedia-tls, the reasons that 
Identity chose to include the offerer's SDP in its signature 
should be applicable to the answerer's SDP.  Otherwise we're
saying the answerer's SDP doesn't need authentication or
integrity protection.

-d

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---

From: Hisham Khartabil <[email-masked]>
Date: Mon, 10 Jul 2006 03:45:15 +0200

I don't think we should mandate UPDATE. INVITE does the job if an 
implementer chooses not to do UPDATE.

Hisham

On May 2, 2006, at 10:23 PM, Elwell, John wrote:

> subsequently. If
> a UA supports a change of From header field URI mid-dialog, as 
> indicated by
> the "id-change" option tag, we could mandate that it also support the 
> SIP
> UPDATE method. Then the peer UA in a dialog would be free to use the 
> UPDATE
> method to report connected identity, rather than the less suitable 
> re-INVITE
> method. The use of UPDATE means 2 messages instead of 3 and avoids the 
> need
> John