Subject: [Sip] Use of SIP and SIPS URIs in Refer-to header

From: Elwell John <[email-masked]>
Date: Wed, 21 Sep 2005 17:13:29 +0100

Robert,

I have been unable to find any guidance on the use of SIP and SIPS URIs in
the Refer-to header in either the REFER RFC or the cc-transfer draft.
Suppose the UAC for a REFER request places a SIPS URI in the Refer-to header
and that the UAS does not support TLS. In this case the UAS for the REFER
request would be unable to issue the required SIPS request. Should it send a
NOTIFY with response code 404, or should it make the referred request using
the SIP URI scheme? If the former, is it reasonable to repeat the REFER
request with a SIP URI in the Refer-to header?

John

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From: "Dale R. Worley" <[email-masked]>
Date: Wed, 21 Sep 2005 13:18:21 -0400

On Wed, 2005-09-21 at 17:13 +0100, Elwell John wrote:
> I have been unable to find any guidance on the use of SIP and SIPS
> URIs in the Refer-to header in either the REFER RFC or the cc-transfer
> draft. Suppose the UAC for a REFER request places a SIPS URI in the
> Refer-to header and that the UAS does not support TLS. In this case
> the UAS for the REFER request would be unable to issue the required
> SIPS request. Should it send a NOTIFY with response code 404, or
> should it make the referred request using the SIP URI scheme?

Definitely it should not make the request using sip:, as that has a
lower security level than what was requested.  It should either respond
to the REFER with an error (416 Unsupported URI Scheme seems most
appropriate), or if it must generate 202 Accepted, do a NOTIFY with 416
or other error response.

> If the former, is it reasonable to repeat the REFER request with a SIP
> URI in the Refer-to header?

Certainly not automatically.  But under guidance from the user, it would
be reasonable.

Dale

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From: Robert Sparks <[email-masked]>
Date: Wed, 21 Sep 2005 18:24:51 -0500

inline
On Sep 21, 2005, at 11:13 AM, Elwell John wrote:

> URIs in the Refer-to header in either the REFER RFC or the cc- 
> transfer draft. Suppose the UAC for a REFER request places a SIPS  
> URI in the Refer-to header and that the UAS does not support TLS.  
> In this case the UAS for the REFER request would be unable to issue  
> the required SIPS request. Should it send a NOTIFY with response  
> code 404, or should it make the referred request using the SIP URI  
> scheme? If the former, is it reasonable to repeat the REFER request  
> with a SIP URI in the Refer-to header?
>
> John
>
The REFER recipient would reject the REFER in this case. Same as if
the URI was to an http: URI and the receiving agent didn't know what to
do with those.

RjS