Hi Alex, 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. Regards,Jay
On Monday, August 15, 2016 5:46 PM, Alex Balashov abalashov@evaristesys.com wrote:
On 08/15/2016 05:42 PM, Jay Li wrote:
Dear All,
I just have a basic SIP question on re-invite. I wonder if "ACK" is required in a re-invite scenario, like re-invite -> 200 OK -> ACK. What I've seen is for some reason, my PSTN doesn't send a "ACK" back to me after my 200 OK response to their re-invite. I don't know if not sending an ACK in a re-invite is an allowed behavior. Thanks.
Yes, an ACK is required. Per RFC 3261 § 14.1 ("UAC behavior"):
The rules for transmitting a re-INVITE and for generating an ACK for a 2xx response to re-INVITE are the same as for the initial INVITE (Section 13.2.1).