Andreas Bystr�m wrote:
Hi all!
A question about To tags. This is the scenario I have in mind:
* UA1 calls [EMAIL PROTECTED] via the proxy P. * P knows that [EMAIL PROTECTED] should be forwarded to UA2. * UA2 responds to the Invite with a 180 Ringing and has added a To tag to the response. * After a period of time, logic in P notices that UA2 hasn't answered the call yet. Then P has instructions to try at UA3 instead, so it sends Cancel to UA2 and sends the origianl Invite to UA3. * UA3 now answers with 180 Ringing with a new To tag since it has no idea of the To tag that UA2 sent. * UA3 send 200 OK and the call is set up.
My quesiton is that isn't not allowed to change the To tag within a dialog since it is used to identify a call? Is it possible to do my scenario? Could it be solved in that way that before P forwards the Invite to UA3, it adds tha To tag that UA2 sent in the first 180? I think I've read somewhere that you are not allowed to put the To tag inside an Invite (if it is not an re-Invite), is this correct? Should I solve the forward on no reply in some other way?
The UAC has no way of knowing whether P exists or not, whether P will parallel or serial fork the request, etc. Either way, what you have here is two early dialogs being established, each distinguished by its unique To-tag.
Once the 2nd dialog results in a 200, the other early dialog is irrelevant.
Paul
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