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Calls diverted to UM not using Media Bypass RRS feed

  • Question

  • We have a Lync branch site with an SBA and PSTN gateway using Media Bypass. Calls from the PSTN that are answered by endpoints are using bypass correctly, but if a call is not answered and goes to UM voicemail, the media stream is mediated (gateway -> mediation server on SBA -> UM server).

    I confirmed that the Lync UM dial plan is set to "secured," so it is using SRTP. Also tested direct calls to subscriber access, and internal (lync-to-lync) calls that divert to UM voicemail also connect directly.

    Is this expected behavior?

    Thursday, May 1, 2014 7:00 PM

All replies

  • For each call to the PSTN, the Mediation Server determines whether media from the endpoint of origin can be sent directly to a Mediation Server peer without traversing the Mediation Server. The peer can be a PSTN gateway, IP-PBX, or Session Border Controller (SBC) at an Internet telephony service provider (ITSP).


    Lisa Zheng
    TechNet Community Support

    Friday, May 2, 2014 8:49 AM
  • Thanks for copy-and-pasting something directly out of the Lync TechNet article on Media Bypass. I know how it works. Do you have any relevant experience on your Lync deployments that use Media Bypass and UM that you can share?
    Friday, May 9, 2014 4:03 PM
  • I haven't done a deep dive, but I can tell you that I've also experienced it.  The situation I had was an issue where a SIP provider was sending an RTP BYE packet early in the G.711 conversation for no decent reason.  Lync server basically saw this and killed audio in one direction for 19-20 seconds.  After that time, audio picked up fine.  What we determined was the the Lync phones were more tolerant of this odd behavior from the Telco, so we turned on media bypass.  That worked well, except we saw what you're seeing with UM, and we were still missing the first 20 seconds of audio, which meant messed up voicemail.  We ended up using another method to resolve it.

    To sum up that ramble, I've seen it too.  You're not alone. 


    Please remember, if you see a post that helped you please click "Vote As Helpful" and if it answered your question please click "Mark As Answer". SWC Unified Communications

    Friday, May 9, 2014 4:22 PM
  • I'm bumping this up to see if anyone has additional insight or to see if you have what you need.


    Please remember, if you see a post that helped you please click "Vote As Helpful" and if it answered your question please click "Mark As Answer". SWC Unified Communications

    Tuesday, May 20, 2014 2:10 PM
  • This looks like it may be related to the implicit use of X-MSRTA when UM is configured to work with Lync. Our gateways cannot talk msrta, but from documentation I have seen, UM will automatically prefer it as the on-the-wire codec when a Lync dialplan is configured and the voicemail storage codec is either MP3 or WMA.

    Monday, September 29, 2014 5:56 PM