[SR-Users] Is ACK required in a re-invite?

[Jay Li]

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.
Regards,Jay
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