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<p class="MsoNormal"><span style="color:#1F497D">Daniel,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">It seems to me like CUCM is waiting for an answer to the offer it sent in the 183 w/SDP. In a non-transfer scenario, does the Nortel side normally send a PRACK at that point? Possibly the Nortel side is sending
the Update before the PRACK?<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D">Brian<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> cisco-voip [mailto:cisco-voip-bounces@puck.nether.net]
<b>On Behalf Of </b>Daniel Pagan<br>
<b>Sent:</b> Thursday, February 13, 2014 5:08 PM<br>
<b>To:</b> cisco-voip@puck.nether.net<br>
<b>Subject:</b> [cisco-voip] SIP Stack & Trace Question<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b>Folks</b>:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’m reviewing an issue and looking for some feedback on a specific SIP stack error. In a nutshell, what appears to be happening is CUCM (8.6.2.24090-1) responding to an UPDATE request with a 500 Internal Server Error in a very specific
transfer call flow:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b>.::: Call is established :::<o:p></o:p></b></p>
<p class="MsoNormal"><b>.::: Nortel Begins a xfer to CUCM :::<o:p></o:p></b></p>
<p class="MsoNormal"><b><o:p> </o:p></b></p>
<p class="MsoNormal"><b><span style="font-size:12.0pt">Nortel ==== CUCM<o:p></o:p></span></b></p>
<p class="MsoNormal"><b>>>> INVITE w/SDP<o:p></o:p></b></p>
<p class="MsoNormal"><b> 100 Trying <<<<o:p></o:p></b></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:#4A452A">=======DA Successful<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#4A452A">=======Outbound to ITSP<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#4A452A">=======MTP Required on Rx SIP Trunk<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#4A452A">=======MTP resource allocated<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#4A452A">=======SDI trace events show </span>
<b><span style="font-size:10.0pt;color:#4A452A">SIPInterface-(292194)::handleOutgoing<u>SDPAnswer</u></span></b><span style="font-size:10.0pt;color:#4A452A">
</span><span style="color:#4A452A">once media info is collected for MTP<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b> 183 w/ SDP </b><b><span style="font-size:9.0pt">(for MTP)</span> <<<<o:p></o:p></b></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="color:#4A452A">=====ITSP returns 183 w/ SDP<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b> 183 <u>no</u> SDP <<<<o:p></o:p></b></p>
<p class="MsoNormal"><b>>>> UPDATE w/SDP<o:p></o:p></b></p>
<p class="MsoNormal"><b><o:p> </o:p></b></p>
<p class="MsoNormal"><span style="color:#4A452A">=====SIP stack detects an existing connection<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#4A452A">=====SIP stack detects an SDP offer has yet to be answered<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><b> 500 Internal Svr Error <<<<o:p></o:p></b></p>
<p class="MsoNormal"><b> w/ retry-timer header<o:p></o:p></b></p>
<p class="MsoNormal"><b> ::: Call Xfer attempt fails :::<o:p></o:p></b></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The SIP stack trace excerpt that raised a flag states<b>:<o:p></o:p></b></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Courier New";color:red">SIP/Stack/Error/0x0/Last Offer not answered yet</span></b><b><span style="font-family:"Courier New";color:red"><o:p></o:p></span></b></p>
<p class="MsoNormal">This occurs after the UPDATE w/ SDP offer is received and immediately before the 500 response is generated.<o:p></o:p></p>
<p class="MsoNormal">SDI traces show the event was added to the UAS response table using same context ID created for the original INVITE.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">With this error in mind I decided to review the RFC for SIP UPDATE and found a very interesting piece of information:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New";color:black">“If an UPDATE is received that contains an offer, and the UAS has<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New";color:black"> generated an offer (in an UPDATE, PRACK or INVITE) to which it has<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New";color:black"> not yet received an answer, the UAS MUST reject the UPDATE with a 491<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New";color:black"> response.
</span><span style="font-size:10.0pt;font-family:"Courier New";color:#C00000">Similarly, if an UPDATE is received that contains an<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New";color:#C00000"> offer, and the UAS has received an offer (in an UPDATE, PRACK, or<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New";color:#C00000"> INVITE)
<u>to which it has not yet generated an answer</u>, the UAS MUST<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New";color:#C00000"> reject the UPDATE with a 500 response, and MUST include a Retry-After<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:10.0pt;font-family:"Courier New";color:#C00000"> header field with a randomly chosen value between 0 and 10 seconds.”<o:p></o:p></span></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Courier New""><o:p> </o:p></span></b></p>
<p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Courier New""><a href="http://www.rfc-editor.org/rfc/rfc3311.txt">http://www.rfc-editor.org/rfc/rfc3311.txt</a><o:p></o:p></span></b></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The 500 response to the UPDATE does indeed contain a Retry-After header. CUCM did generate an answer (see above) but SIP stack detects the last offer wasn’t answered. Although the Nortel PBX doesn’t reattempt after x seconds, a related
RFC states the UAC *may* reattempt but it’s not a requirement. With that said, I’m wondering if anyone can help answer a few questions:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><b><span style="mso-list:Ignore">1.<span style="font:7.0pt "Times New Roman"">
</span></span></b><![endif]>Has anyone encountered this before?<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><b><span style="mso-list:Ignore">2.<span style="font:7.0pt "Times New Roman"">
</span></span></b><![endif]>Bug toolkit doesn’t return any good matches. Perhaps there’s an internal defect?<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><b><span style="mso-list:Ignore">3.<span style="font:7.0pt "Times New Roman"">
</span></span></b><![endif]>The 2<sup>nd</sup> 183 from CUCM (with no SDP) contains a CSeq header for the original INVITE from Nortel.<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in">This is the most recent provisional from CUCM in response to the offer from Nortel.<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in">My initial thought is CUCM is referring back to this 2<sup>nd</sup> 183 when determining no answer was generated for the last offer. This would explain the 500 response w/ Retry-After header
<u>and</u> the SIP stack error stating that an answer has yet to be generated.<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in">:: Note: Call-ID headers are confirmed to be consistent throughout the SDI traces reviewed
<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in">:: Note: The Allow header contains UPDATE<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in">:: Note: CUBE is not involved in this call-flow<o:p></o:p></p>
<p class="MsoListParagraph" style="text-indent:-.25in;mso-list:l0 level1 lfo2"><![if !supportLists]><b><span style="mso-list:Ignore">4.<span style="font:7.0pt "Times New Roman"">
</span></span></b><![endif]>Can anyone tell me what CCB is in the context of UAS response tables? Seeing quite a few “Adding to Response/Request Table” also piques my interest. Is there anything useful from a troubleshooting standpoint from these tables when
the ccb=<ID> is identified and marked in Notepad++?<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in"><o:p> </o:p></p>
<p class="MsoNormal" style="margin-left:.5in">Thoughts?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks ahead of time.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">- Daniel<o:p></o:p></p>
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