Subject: [Sipping] Use of the REFER in draft-shacham-sipping-session-mobility-01

From: "Alexeitsev, D" <[email-masked]>
Date: Thu, 16 Feb 2006 16:11:01 +0100

Hello All

I have a few questions to the draft-shacham-sipping-session-mobility-01

1) On the several occurrences in the draft there are no explicit method=INVITE statements in the Refer-To header. Does the INVITE method is the default method to contact a resource addressed by the Refer-To header? The RFC 3515 is not very explicit on that:

"2.4.3 Accessing the Referred-to Resource 
The resource identified by the Refer-To URI is contacted using the normal mechanisms for that URI type. For example, if the URI is a SIP URI indicating INVITE (using a method=INVITE URI parameter for example), the UA would issue a new INVITE using all of the normal rules for sending an INVITE defined in [1]."

2) In the following example from the section "5.3.2  Retrieval of a session" how can it be syntaxicly differentiated, that the Replaces header belongs to the INVITE and not the REFER method? Why is it needed to wrap the Replaces URI with the escaped %22 "-sign?

Refer-To:<sip:[email-masked];method=REFER
              ?Refer-To="<sip:[email-masked];audio;
                      video?Replaces=[email-masked];
                      to-tag=aaa;from-tag=bbb%22>">

Greetings,
Denis Alexeitsev

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From: Ron Shacham <[email-masked]>
Date: Thu, 16 Feb 2006 12:45:46 -0500 (EST)

Hi Denis,
Comments inline.

Regards,
Ron

> The resource identified by the Refer-To URI is contacted using the normal mechanisms for that URI type. For example, if the URI is a SIP URI indicating INVITE (using a method=INVITE URI parameter f…

I see how that quote would imply that the INVITE method must be stated
explicitly.  All of the examples there and in related documents (eg. RFC
3892) seem to omit it.  I think someone needs to provide clarity on this.

>                      to-tag=aaa;from-tag=bbb%22>">

The Replaces header is associated with the INVITE since it is included in
the Refer-To URI.

The quotations are escaped to avoid ambiguity, since they are nested 
within the quoted text of the Refer-To URI.  I haven't found double quotes 
discussed in RFC 2396 except that they are used to delimit a URI, although 
RFC 1738 says that it is an unsafe character that must be encoded (Section 
2.2).  I'm not sure about the right way of nesting quotes.

In any case, looking now at some examples, such as
the one in I-D.ietf-sipping-service-examples Section 2.5, the Replaces
value is not quoted within a Refer-To URI.  So this doesn't seem necessary
at all.

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From: "Brett Tate" <[email-masked]>
Date: Thu, 16 Feb 2006 13:10:39 -0500

> 1) On the several occurrences in the draft there are 
> no explicit method=INVITE statements in the Refer-To 
> header. Does the INVITE method is the default method 
> to contact a resource addressed by the Refer-To header?

Per RFC3261 section 19.1.2, the default for sip-uri method parameter is
INVITE.