Hi,
When a CANCEL is received and matches a known INVITE transaction, it is forked to all existing branches of that INVITE transaction, at least with these settings:
modparam("tm", "cancel_b_method", 2) modparam("tm", "failure_reply_mode", 3)
I have a mobile endpoint that is slow to be pushed awake and reregister, tsilo-style, and by the time it finally appears on the scene, the underlying INVITE transaction has been terminated. Accordingly, that endpoint receives no CANCEL.
You might ask why that's a problem, if it also didn't receive a forked INVITE. The problem is that Apple's CallKit requires interactive presentation of VoIP APNS notifications as though they are "calls", leading to the phenomenon of what might be called "ghost calls" extrinsically to the actual mobile application.
Anyway, I am aware of numerous possible solutions to this problem in principle; most involve sending an out-of-band SIP message to signify an alternative cancellation of the call. However, wonder if I am missing some best-practical approach, perhaps through an overlooked TM facility, or some way of keeping the transaction alive longer than the CANCEL from the UAC would ordinarily require? I don't see how that would work, but thought better to ask.
Thanks!
-- Alex