Bad quality on voice calls - UDP checksum offload

Discussion in 'General' started by possebon, Mar 17, 2009.

  1. possebon

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    Hi all,

    I've been researching a way to improve the quality of the call using Elastix 1.3.2 and Vono Provider.

    I'm using the wireshark to capture the traffic between my elastix server and vono server.

    I captured the first traffic using only the softphone provided by Vono

    After I captured a lot of traffics, each one with different codec selection, to see if what could be wrong.

    One thing that I noticed: all calls that passes through Elastix, has this error on Wireshark:

    Checksum: 0xf086 [incorrect, should be 0x0bb6 (maybe caused by "UDP checksum offload"?)]


    Any ideas about this issue?

    Thanks in advance
     
  2. Chilling_Silence

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    This may be of interest to you:
    http://lists.iptel.org/pipermail/serdev ... 11645.html

    When you say "improve the call quality", please expand on what you mean? Whats specifically 'bad' about it? Have you tried different softphones on different PC's? As Softphones reliability / quality varies so much its not even funny ... ;)
     
  3. danardf

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    Hi.

    Maybe if you make the VoIP, you must use the QoS.
    All UDP (RTP) packets must have the high priority.
     
  4. possebon

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    Re:Bad quality on voice calls - UDP checksum offlo

    Well, I'll try explain with more details.

    Vono is a VoIP provider in Brazil and they are one of the biggest VoIP providers (there).

    They provide a softphone (like VoIPbuster or VoIPCheap does). If we use this softphone provided by Vono, all calls made through the Vono account are perfect.

    We have implemented Elastix 1.3.2 and we are using Vono as our SIP trunk. The clients are using the X-Lite as softphone. The Elastix is using exactly the same internet link as the clients (i.e. it does not matter if you use the Vono softphone or the Elastix, the internet connection is the same).

    When the calls are made using X-Lite, the clients can hear the other part perfectly, but the other parts, listen the clients with cuts or with noise.

    My first shot was related with codecs. I've tried all codecs combination, and did not get better. In some cases it was worst.

    So, I decided check what codec the Vono softphone is using. This softphone is closed, there is no way to see this information on it, so I did the capture of the traffic directly on PC with softphone with Wireshark. If this capture I identified that the codec used is ILBC.



    I tried to enable ILBC on Elastix, and after a lot of research discovered that after 1.4.18 asterisk version, ILBC it's not included.

    Anyway, I figured out a way to get again the ILBC (I posted my solution on this forum too), and it's enabled right now.

    After all this work, nothing improved the calls.

    So with the same capture, and with a capture made directly on Elastix server I identified this UDP checksums. Actually I fixed (yesterday) the problem of UDP checksum, using this: ethtool -K rx off tx off

    The calls are still cutting or with some noise to the other parts.

    I digged a little bit more on capture and find out another difference (RTP stream analysis), that Vono softphone is sending something like "Comfort noise".

    I researched how to do it on Asterisk, and seems that Asterisk does not support this.

    Sorry for the long long post, but I'm trying to give details as much as possible.

    I'll attach some screenshots of my analysis too.
     
  5. possebon

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    Re:Bad quality on voice calls - UDP checksum offlo

    Vono Capture - ILBC
    [​IMG]
     
  6. possebon

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    Re:Bad quality on voice calls - UDP checksum offlo

    Vono - Comfort Noise
    [​IMG]
     
  7. possebon

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    Re:Bad quality on voice calls - UDP checksum offlo

    Elastix Catpure Traffic - UDP checksum (black lines)
    [​IMG]
     
  8. possebon

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    Re:Bad quality on voice calls - UDP checksum offlo

    Elastix (RTP analysis) - No Comfort Noise
    [​IMG]
     
  9. possebon

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    Re:Bad quality on voice calls - UDP checksum offlo

    Elastix - After UPD checksum correction
    [​IMG]
     
  10. possebon

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    Re:Bad quality on voice calls - UDP checksum offlo

    Elastix (RTP analysis) - after UDP checksum correction - No Comfort Noise
    [​IMG]
     
  11. Chilling_Silence

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    Re:Bad quality on voice calls - UDP checksum offlo

    A few things come to mind here.
    Unfortunately the pics aren't working for me so I cant see everything but it sounds like you're pretty handy with Wireshark :D

    Anyways, in my limited experience with things like VoIPStunt / VoIPBuster etc you always appear to get better quality directly from their softphone client. Last time I looked they were using the GSM codec. If they've upgraded to iLBC then all the better I would say! As a codec, I absolutely love it and think its brilliant!

    So, a couple of things:
    1) The official softphones, what happens if you load up 3-4 machines and make concurrent phone calls?
    2) QoS, what kind of QoS have you got going? The more I work with VoIP the more I realize how much a good QoS system is absolutely crucial.
    3) Hardware / software setup, Im presuming the only thing you're changing is closing down the Vono Softphone, registering the trunk in Elastix, then opening up X-Lite? Can I recommend you also try ZoIPer and OpenWengo? See what results they give?

    We've got 5 boxes here, and each gets 'better' results with different softphone, its truly weird and unexplainable. Two work better with OpenWengo, two work better with ZoIPer, and one works best with X-Lite.

    Let us know how you go :)

    Cheers


    Chill.
     

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