<html><head></head><body><div style="color:#000; background-color:#fff; font-family:HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif;font-size:16px"><div id="yui_3_16_0_ym19_1_1471300057148_3234"><span id="yui_3_16_0_ym19_1_1471300057148_3388">Hi Alex,</span></div><div id="yui_3_16_0_ym19_1_1471300057148_3234"><br></div><div id="yui_3_16_0_ym19_1_1471300057148_3234" dir="ltr">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.</div><div id="yui_3_16_0_ym19_1_1471300057148_3234" dir="ltr"><br id="yui_3_16_0_ym19_1_1471300057148_3550"></div><div id="yui_3_16_0_ym19_1_1471300057148_3234" dir="ltr">Regards,</div><div id="yui_3_16_0_ym19_1_1471300057148_3234" dir="ltr">Jay </div> <div class="qtdSeparateBR"><br><br></div><div class="yahoo_quoted" style="display: block;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div style="font-family: HelveticaNeue, Helvetica Neue, Helvetica, Arial, Lucida Grande, sans-serif; font-size: 16px;"> <div dir="ltr"><font size="2" face="Arial"> On Monday, August 15, 2016 5:46 PM, Alex Balashov <abalashov@evaristesys.com> wrote:<br></font></div> <br><br> <div class="y_msg_container">On 08/15/2016 05:42 PM, Jay Li wrote:<div class="yqt7030462825" id="yqtfd73579"><br clear="none">> Dear All,<br clear="none">><br clear="none">> I just have a basic SIP question on re-invite. I wonder if "ACK" is<br clear="none">> required in a re-invite scenario, like re-invite -> 200 OK -> ACK. What<br clear="none">> I've seen is for some reason, my PSTN doesn't send a "ACK" back to me<br clear="none">> after my 200 OK response to their re-invite. I don't know if not sending<br clear="none">> an ACK in a re-invite is an allowed behavior. Thanks.</div><br clear="none"><br clear="none">Yes, an ACK is required. Per RFC 3261 ยง 14.1 ("UAC behavior"):<br clear="none"><br clear="none"> The rules for transmitting a re-INVITE and for<br clear="none"> generating an ACK for a 2xx response to re-INVITE are<br clear="none"> the same as for the initial INVITE (Section 13.2.1).<br clear="none"><br clear="none">-- <br clear="none">Alex Balashov | Principal | Evariste Systems LLC<br clear="none">1447 Peachtree Street NE, Suite 700<br clear="none">Atlanta, GA 30309<br clear="none">United States<br clear="none"><br clear="none">Tel: +1-800-250-5920 (toll-free) / +1-678-954-0671 (direct)<br clear="none">Web: <a shape="rect" href="http://www.evaristesys.com/," target="_blank">http://www.evaristesys.com/, </a><a shape="rect" href="http://www.csrpswitch.com/" target="_blank">http://www.csrpswitch.com/</a><br clear="none"><br clear="none">_______________________________________________<br clear="none">SIP Express Router (SER) and Kamailio (OpenSER) - sr-users mailing list<br clear="none"><a shape="rect" ymailto="mailto:sr-users@lists.sip-router.org" href="mailto:sr-users@lists.sip-router.org">sr-users@lists.sip-router.org</a><br clear="none"><a shape="rect" href="http://lists.sip-router.org/cgi-bin/mailman/listinfo/sr-users" target="_blank">http://lists.sip-router.org/cgi-bin/mailman/listinfo/sr-users</a><div class="yqt7030462825" id="yqtfd73481"><br clear="none"></div><br><br></div> </div> </div> </div></div></body></html>