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<p>Hello,</p>
<p>there is an errata for that RFC, but it refers only to the BYE,
where it adds back the transport=tcp, but the ACK R-URI should
follow the same rules, see:</p>
<p> * <a href="https://www.rfc-editor.org/errata/eid5294">https://www.rfc-editor.org/errata/eid5294</a></p>
<p>Cheers,<br>
Daniel<br>
</p>
<div class="moz-cite-prefix">On 28.04.19 22:54, Yufei Tao wrote:<br>
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<p class="MsoNormal">Hi,</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I have a question regarding basic SIP flow
for establishing a call session, and wonder if anyone can help
me clarify.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">For normal call set up, INVITE-OK-ACK, from
RFC3261, I believe the ACK’s R-URI should be a copy of the
Contact header of the OK message. </p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">However in RFC3665 sections 3.1 and 3.2 for
example, the ACK’s R-URI missed the parameters from the
Contact header of the OK, e.g.</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">In OK the Contact header is:</p>
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<pre><span style="color:black"> Contact: <a class="moz-txt-link-rfc2396E" href="sip:bob@client.biloxi.example.com;transport=tcp"><sip:bob@client.biloxi.example.com;transport=tcp></a><o:p></o:p></span></pre>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">And ACK the R-URI is:</p>
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<pre><span style="color:black">ACK <a class="moz-txt-link-freetext" href="sip:bob@client.biloxi.example.com">sip:bob@client.biloxi.example.com</a> SIP/2.0<o:p></o:p></span></pre>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Which has got the parameter ‘transport=tcp’
removed – why is this?</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">In this case if the proxy connected to Bob
handles ACK in the usual way as it would for all in-dialog
requests, i.e. based on routing headers only and not extra
processing, it’ll try to relay the ACK message to Bob using
the default transport UDP which is not expected and will fail.
</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Can anyone help explain why the parameters
are removed in RFC3665 examples please? Have I missed
anything? Thank you very much!</p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Yufei</p>
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<pre class="moz-signature" cols="72">--
Daniel-Constantin Mierla -- <a class="moz-txt-link-abbreviated" href="http://www.asipto.com">www.asipto.com</a>
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