On 08/15/2016 06:33 PM, Jay Li wrote:
Thanks for the quick response. I don't have much experience with SIP. I just wonder if you've seen PSTN providers not send an ACK back to a re-invite? With your professional experience, is this common? Thanks.
Certainly, not sending end-to-end ACKs for 2xx responses is a problem that occurs, both for initial and in-dialog invites (reinvites).
However, it indicates that something is misconfigured or improperly implemented somewhere, and is a serious issue that needs to be addressed.