Hi Marc,

Its close. According to RFC 3261, the 200 for the CANCEL should not have a tag.

         1xx and 2xx responses may be involved in the establishment of
         dialogs.  When a request does not contain a To tag, the To tag
         in the response is used by the UAC to distinguish multiple
         responses to a dialog creating request.  A proxy MUST NOT
         insert a tag into the To header field of a 1xx or 2xx response
         if the request did not contain one.  A proxy MUST NOT modify
         the tag in the To header field of a 1xx or 2xx response.

Cheers,
Charles


Marc Petit-Huguenin wrote:
Hi,

Section 9.2 says that the To tag in a response to a CANCEL should be the
same than the To tag in the response to the original request.

My understanding is that this rule only applies to an UAS, and not to a
proxy, as a proxy can send multiple responses with different To tags.

Section 16.10 seems to support this, as it says that "[...] the element
is acting as a user agent server as defined in Section 8.2." No words
about reusing a previous To tag.

So my question is: Is this call-flow correct?

UAC            Proxy
  | INVITE        |
  |-------------->|
  |               |
  | 100 tag=null  |
  |<--------------|
  |               |
  | 180 tag=a     |
  |<--------------|
  |               |
  | 180 tag=c     |
  |<--------------|
  |               |
  | CANCEL        |
  |-------------->|
  |               |
  | 200 tag=d     |
  |<--------------|
  |               |
  | 487 tag=a     |
  |<--------------|
  |               |
  | ACK           |
  |-------------->|
  |               |



P.S.: The Bugzilla database at http://www.sipwg.org/sipwg/query.cgi
seems to be down.




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