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<p><font size="-1">Ben,</font></p>
<p><font size="-1">Thank you that is so helpful.</font></p>
<p><font size="-1">Adrian.</font><br>
</p>
<br>
<div class="moz-cite-prefix">On 24/01/18 19:35, Ben Newlin wrote:<br>
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<p class="MsoNormal">Adrian,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I can’t help with a way not to increment
the version number on RTPProxy, but I believe I know why the
provider is not happy with the exchange.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The problem is not that the version number
has incremented without a change to the SDP. As you have
pointed out, RFC 4566 does not prohibit changing the version
number and I think the provider was wrong to point you to that
RFC. I think it’s likely the issue isn’t with the SDP itself,
but with the exchange. It is covered in RFC 3261, Section
13.2.1, specifically these two bullets:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph"
style="text-indent:-.25in;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span
style="font-size:10.0pt;font-family:Symbol;color:black"><span
style="mso-list:Ignore">·<span style="font:7.0pt
"Times New Roman"">
</span></span></span><!--[endif]--><span
style="font-size:10.0pt;font-family:"Courier
New";color:black">If the initial offer is in an INVITE,
the answer MUST be in a<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Courier
New";color:black"> reliable non-failure message
from UAS back to UAC which is<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Courier
New";color:black"> correlated to that INVITE.
For this specification, that is<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Courier
New";color:black"> only the final 2xx response
to that INVITE. That same exact<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Courier
New";color:black"> answer MAY also be placed in
any provisional responses sent<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Courier
New";color:black"> prior to the answer. The
UAC MUST treat the first session<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Courier
New";color:black"> description it receives as
the answer, and MUST ignore any<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Courier
New";color:black"> session descriptions in
subsequent responses to the initial<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Courier
New";color:black"> INVITE.<o:p></o:p></span></p>
<pre style="margin-left:.5in;text-indent:-.25in;mso-list:l0 level1 lfo1"><!--[if !supportLists]--><span style="font-family:Symbol;color:black"><span style="mso-list:Ignore">·<span style="font:7.0pt "Times New Roman""> </span></span></span><!--[endif]--><span style="color:black">Once the UAS has sent or received an answer to the initial<o:p></o:p></span></pre>
<pre><span style="color:black"> offer, it MUST NOT generate subsequent offers in any responses<o:p></o:p></span></pre>
<pre><span style="color:black"> to the initial INVITE. This means that a UAS based on this<o:p></o:p></span></pre>
<pre><span style="color:black"> specification alone can never generate subsequent offers until<o:p></o:p></span></pre>
<pre><span style="color:black"> completion of the initial transaction.<o:p></o:p></span></pre>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">So the problem is that the SDP is changing
between the 183 and 200 OK, even though it is only the
version. When providing SDP in an unreliable response, the SDP
in the final response is required to be exactly the same. You
are not allowed to change the SDP once it has been sent
without initiating a new offer/answer, which you can’t do in
the 200 OK as you haven’t completed the previous exchange with
a final response.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Having said that, this is not a widely
enforced rule. Nearly all SIP implementations are tolerant of
this or at least will simply ignore SDP’s after the first
without terminating the call. Many even support receiving
multiple different SDP’s in multiple 183 responses during a
single INVITE exchange. But I have worked with some who do not
tolerate it and unfortunately the RFC is on their side.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Of course, only your provider can confirm
if this is, in fact, their issue with the exchange.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Ben<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><b><span
style="font-size:12.0pt;color:black">From: </span></b><span
style="font-size:12.0pt;color:black">Users
<a class="moz-txt-link-rfc2396E" href="mailto:users-bounces@lists.opensips.org"><users-bounces@lists.opensips.org></a> on behalf of
Adrian Fretwell <a class="moz-txt-link-rfc2396E" href="mailto:adrian.fretwell@topgreen.co.uk"><adrian.fretwell@topgreen.co.uk></a><br>
<b>Reply-To: </b>OpenSIPS users mailling list
<a class="moz-txt-link-rfc2396E" href="mailto:users@lists.opensips.org"><users@lists.opensips.org></a><br>
<b>Date: </b>Wednesday, January 24, 2018 at 2:06 PM<br>
<b>To: </b>OpenSIPS users mailling list
<a class="moz-txt-link-rfc2396E" href="mailto:users@lists.opensips.org"><users@lists.opensips.org></a><br>
<b>Subject: </b>[OpenSIPS-Users] SDP version increment
without a change in SDP<o:p></o:p></span></p>
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<div>
<p class="MsoNormal"><o:p> </o:p></p>
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<p><a name="_MailOriginalBody" moz-do-not-send="true"><span
style="font-size:10.0pt">Hello All, I have an issue for
which I have not been able to find a definitive answer in
the RFCs.</span><o:p></o:p></a></p>
<p><span style="mso-bookmark:_MailOriginalBody"><span
style="font-size:10.0pt">I use RTPProxy as part of NAT
traversal so RTP streams are set up between upstream
provider and my proxy, and between my proxy and the UAC.</span><o:p></o:p></span></p>
<p><span style="mso-bookmark:_MailOriginalBody"><span
style="font-size:10.0pt">The problem I have, is UAC
changes it's RTP port between 183 and 200 OK and thus
increments the SDP version number, BUT the ports DO NOT
change between proxy and upstream provider but the SDP
version number does, because it is passed through. The
upstream provider says this violates RFC 4566 and sends an
immediate BYE after the final ACK.</span><o:p></o:p></span></p>
<p><span style="mso-bookmark:_MailOriginalBody"><span
style="font-size:10.0pt">I read that RFC 4566 says:
</span><o:p></o:p></span></p>
<p><span style="mso-bookmark:_MailOriginalBody"><span
style="font-size:10.0pt">" <i>
<sess-version> is a version number for this
session description. Its<br>
usage is up to the creating tool, so long as
<sess-version> is<br>
increased when a modification is made to the
session data. Again,<br>
it is RECOMMENDED that an NTP format timestamp is
used</i>."</span><o:p></o:p></span></p>
<p><span style="mso-bookmark:_MailOriginalBody"><span
style="font-size:10.0pt">The problem is I can't find an
RFC stating "You MUST NOT increment<br>
version number if no change is made to the SDP".</span><o:p></o:p></span></p>
<p><span style="mso-bookmark:_MailOriginalBody"><span
style="font-size:10.0pt">So I must either:
</span><o:p></o:p></span></p>
<p><span style="mso-bookmark:_MailOriginalBody"><span
style="font-size:10.0pt">1. Prove that it should be OK to
increment the version number without any change to the
SDP. Or</span><o:p></o:p></span></p>
<p><span style="mso-bookmark:_MailOriginalBody"><span
style="font-size:10.0pt">2. Find a way of not passing
through the incremented version number to the upstream
side where the SDP has not actually changed.</span><o:p></o:p></span></p>
<p><span style="mso-bookmark:_MailOriginalBody"><span
style="font-size:10.0pt">I hope that makes sense... As
always any help very nuch appreciated.</span><o:p></o:p></span></p>
<div>
<p class="MsoNormal"><span
style="mso-bookmark:_MailOriginalBody"><span
style="font-size:10.0pt;font-family:"Verdana",sans-serif">Kind
regards,<br>
<br>
Adrian Fretwell<br>
Nottinghamshire<br>
UK</span></span><span
style="mso-bookmark:_MailOriginalBody"><o:p></o:p></span></p>
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