<div dir="ltr"><div dir="ltr"><div>Hi Guillermo,</div><div><br></div><div>This flow looks just fine and is very common especially in mobile networks, where a bearer is being established before the B party answers. This allows to play an early media to the A-party in first place, but together with UPDATE/200, it also allows both parties to renegotiate the codec even before the call is answered (e.g. in CSFB scenarios).<br></div><div><br></div><div>Take a look at RFC3261:</div><div>"<br><pre class="gmail-newpage"><span class="gmail-h4"><h4><a class="gmail-selflink" name="section-13.2.1" href="https://tools.ietf.org/html/rfc3261#section-13.2.1">13.2.1</a> Creating the Initial INVITE</h4></span></pre>
[...]<pre class="gmail-newpage"> o If the initial offer is in an INVITE, the answer MUST be in a
reliable non-failure message from UAS back to UAC which is
correlated to that INVITE. For this specification, that is
only the final 2xx response to that INVITE. That same exact
answer MAY also be placed in any provisional responses sent
prior to the answer. The UAC MUST treat the first session
description it receives as the answer, and MUST ignore any
session descriptions in subsequent responses to the initial
INVITE.</pre>
"</div><div>For your case the "<span style="font-family:courier new,monospace">reliable non-failure message from UAS back to UAC which is correlated to that INVITE</span>" is this 183 with SDP, because is is followed by PRACK+200. There should be no more SDP answers after this provisional (and reliably delivered) reply. You can find more on this topic in RFC3262:</div><div>"
<pre class="gmail-newpage"><font size="1"><span class="gmail-h2"><h2><a class="gmail-selflink" name="section-5" href="https://tools.ietf.org/html/rfc3262#section-5">5</a> The Offer/Answer Model and PRACK</h2></span></font></pre>
<pre class="gmail-newpage"> If the INVITE contained an offer, the UAS MAY generate an answer in a
reliable provisional response (assuming these are supported by the
UAC). That results in the establishment of the session before<br> completion of the call.
"<br></pre></div><div>This call flow was also
described
in RFC 6337 as "Pattern 3".</div><div><br></div><div>P.S.: To be able to try to help you with the audio issue, I would need to look into pcap trace of the call.<br></div><div><br></div><div>BR,</div><div>Tomasz.<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">czw., 20 cze 2019 o 19:41 Zuñiga, Guillermo <<a href="mailto:Guillermo.Zuniga@cwpanama.com">Guillermo.Zuniga@cwpanama.com</a>> napisał(a):<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div lang="ES-PA">
<p class="gmail-m_-4664586527859629690f1fd8ef2-de04-4a74-a01f-b952c9aa1b3b"></p>
<div class="gmail-m_-4664586527859629690WordSection1">
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">Hi fellows,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">I would like to know the following:<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">I am having the following flow and I would like to know if is a valid flow and if the remote SIPGW should be able to handle or complete this dialog when receive a
200OK without SDP to the INVITE.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">Flow:<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">A ->INVITE with SDP<u></u><u></u></span></p>
<p class="MsoNormal" style="margin-left:283.2pt"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">B<-TRYING<u></u><u></u></span></p>
<p class="MsoNormal" style="margin-left:283.2pt"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">B<-183 WITH SDP<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">A->PRACK<u></u><u></u></span></p>
<p class="MsoNormal" style="margin-left:247.8pt;text-indent:35.4pt"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">B<-200OK TO THE PRACK<u></u><u></u></span></p>
<p class="MsoNormal" style="margin-left:247.8pt;text-indent:35.4pt"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">B<-180 RINGING WITHOUT SDP<u></u><u></u></span></p>
<p class="MsoNormal" style="margin-left:247.8pt;text-indent:35.4pt"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">B<-200OK WITHOUT SDP TO THE INVITE.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">A->ACK TO THE 200OK WITHOUT SDP TO THE INVITE.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">My question comes, cause I am having audio issue with the client is calling us and here I would like to know if could be related that I am sending the 200OK without
SDP. Or he should be able to complete the dialog cause previous to the 200OK without SDP I sent a 183 with SDP?<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">Please let me know any comments or where in the RFC I can look for that describe this behavior.<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US"><u></u> <u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">Regards,<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US">Guillermo<u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-family:"Arial","sans-serif";color:rgb(31,73,125)" lang="EN-US"><u></u> <u></u></span></p>
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