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--></style></head><body lang=EN-US link="#0563C1" vlink="#954F72" style='word-wrap:break-word'><div class=WordSection1><p class=MsoNormal>Hi,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I have experienced out of order packet processing when testing a simple Kamailio config.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The configuration is as follows, basically:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=p1><span class=s1>request_route{</span><o:p></o:p></p><p class=p1><span class=apple-converted-space> </span><span class=s1>record_route()</span><span class=s2>;</span><o:p></o:p></p><p class=p2><o:p> </o:p></p><p class=p1><span class=apple-converted-space> </span><span class=s1>enum_query()</span><span class=s2>;</span><o:p></o:p></p><p class=p1><span class=apple-converted-space> </span><span class=s1>xlog("INVITE ENUM query - To URI $tU")</span><span class=s2>;</span><o:p></o:p></p><p class=p1><span class=apple-converted-space> </span><span class=s1>forward()</span><span class=s2>;</span><o:p></o:p></p><p class=p1><span class=s1>}</span><o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>I saw this thread from 2020:<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='color:black'><a href="https://www.mail-archive.com/sr-users@lists.kamailio.org/msg11786.html"><span style='font-size:10.5pt;font-family:Roboto;color:#1155CC'>https://www.mail-archive.com/sr-users@lists.kamailio.org/msg11786.html</span></a><o:p></o:p></span></p><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:black'>The issue seems to be that kamailio process scheduling is naïve – i.e., incoming SIP packets are processed without regard to whether packets received before this one, are currently being processed. This means any packets after the initial INVITE that require more processing, can get reordered. <o:p></o:p></span></p><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:black'>In my test lab I have:<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'> SIPp – UAC<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'> Kamailio Proxy<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'> SIPp – UAS<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:black'>The proxy uses enum NAPR lookups to route calls to +13038151000 to the UAS.<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:black'>Now, if I do SIPp UAC o SIPp UAS directly, I have no problems – no out of order packets.<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:black'>It is only when I introduce Kamailio in the middle that I get OOO packets.<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:black'>See the images attached: uac-to-proxy, proxy, and proxy-to-uas.<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p><p class=MsoNormal>In this example, Kamailio OOO causes SIPp UAC to fail to “generate audio” – because UAC does not see packets in the correct order, I never turns on the simulated audio. Calls that have in-order dialogs, work fine, and SIPP UAC “pauses” 10 seconds to simulate a phone call.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>So far, the error rate runs from 1/1000 to around 1/200 – pretty bad.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:black'>In the thread, a few things were suggested.<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:black'>Have fewer kamailio processes than cores:<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'> Did not resolve issue.<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:black'>Try route_locks_size = 256<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'> Did not resolve issue. Though, it did alter it somewhat. But, it is not clear to me how this works – would this setting restrict the number of open calls to 256?<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:black'>Have only one kamailio process: (“children=1”)<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'> This works. “Works”, I should say, because this would greatly restrict total platform scalability to a point where it is probably useless for my application.<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:black'>I saw the same issue discussed in the OpenSIPS mailing list from 2010, and the response was “this is not a bug”.<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p><p class=MsoNormal><span style='color:black'>Well, I respectfully beg to differ with both OpenSIPS and Kamailio – it IS a bug. I don’t think a proxy should reorder packets involved in a call in a non-deterministic way. In the Kamailio list thread, Alex Balashov discusses the contortions he has to go through to avoid repercussions from this issue.<o:p></o:p></span></p><p class=MsoNormal><span style='color:black'><o:p> </o:p></span></p><p class=MsoNormal>Kamailio as-is probably works fine for relatively low-volume operations. And a lot of the feedback is “why are out of order packets a problem?” OK, sure, in the very specific example given in the 2020 thread, maybe who cares. But in my thinking, there is absolutely nothing preventing Kamailio from generating much more serious OOO scenarios that would cause calls to fail. In my example, Kamailio OOO causes SIPp to fail to “generate audio”. Who knows how other SIP stacks will behave?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>But the more one will try to scale Kamailio, the more significantly this out of order processing issue will become.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>The solution to this seems very simple and straightforward – put packets to be processed into a queue PER Call-ID, or something along those lines.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>In short, the parallelism should be by call, not by packet.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>What say ye? Have I misunderstood something here?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Cheers,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Jawaid<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>