Sending again with proper formatting.
-------
Hi All,

Let's assume a scenario where B2BUA forks the incoming call for a user
to two UA's, UA2 & UA3.

SIP message flow for this is:

UA1                  B2BUA                  UA2         UA3
---------INVITE---------->
       (Call-ID=c1)
       (From tag=f1)
                        ----------INVITE-------->
                             (Call-ID=c2)
                             (From tag=f2)
                        ------------------INVITE------------------>

                                    (Call-ID=c3)
                                    (From tag=f3)
                         <-----------------180----------------------
                                    (Call-ID=c3)
                                    (From tag=f3)
                                    (To tag=t3)
<----------180------------
      (Call-ID=c1)
      (From tag=f1)
      (To tag=t1)
                         <---------180------------
                              (Call-ID=c2)
                              (From tag=f2)
                              (To tag=t2)
                              (Require=100rel)
<----------180------------
     (Call-ID=c1)
     (From tag=f1)
     (To tag=t11)
     (Require=100rel)
                         <-----------------200----------------------
                                    (Call-ID=c3)
                                    (From tag=f3)
                                    (To tag=t3)
                         --------CANCEL--------->
                              (Call-ID=c2)
                              (From tag=f2)
                              (To tag=t2)
                         <--------200--------------

As per our internal design after receiving final response from UA3,
B2BUA will CANCEL the call towards UA2.
But we can't send 200OK to UA1 as a PRACK is pending on
dialog(c1+f1+t11).

Thus I have few queries on it:
1) Can B2BUA send a CANCEL to UA2 before PRACK transaction is over?
2) If answer to above question is "yes" then how can B2BUA send 200OK
for dialog(c1+f1+t1) to UA1?

Are there any alternate & better way to handle this call flow?

Thanks,
Puneet


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