El Thursday 15 May 2008 05:39:32 Allan Chao escribió:

Dear All:

I have found there are some devices can't process two 180 ringing after use OPENSER to do parallel forking, so, i have a idea that is used OPENSER to delete To tag in the To header before relay it , and it works well with eyebeam. But i can't find any spec to support my idea because it is against "early dialog" prograss and my question is

how does UE(eyebeam or some client) to create dialog if there is no any To tag in 180 ringing but 200 OK has in the latter ? i think the UA will generate local ring tone but no any dialog after receives 180 ringing with no To tag? is it right ? thanks,

A "180 Ringing" without To tag is completely anti RFC 3261 compliant so you shouldn't do it:

8.2.6.2 Headers and Tags ... However, if the To header field in the request did not contain a tag, the URI in the To header field in the response MUST equal the URI in the To header field; additionally, the UAS MUST add a tag to the To header field in the response (with the exception of the 100 (Trying) response, in which a tag MAY be present). This serves to identify the UAS that is responding, possibly resulting in a component of a dialog ID. The same tag MUST be used for all responses to that request, both final and provisional (again excepting the 100 (Trying)).

If you have a device not allowing various 180 with different To tag, this is, a device not allowing parallel forking, then it's a bug in that device.