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
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).
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).
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.
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Alex Balashov -
Jay Li