Microsoft Teams and Direct Routing – some calls are failing and marked as missed calls

I had the situation where Microsoft Teams is configured for Direct Routing and calls are dropped unexpectedly. We are using an Audiocodes SBC in Microsoft Azure and a SIP Trunk from Deutsche Telekom for the PSTN connection.

Sometimes an inbound call is signaled by Microsoft Teams for a second and then, it is dropped. In the Microsoft Teams activity feed a missed call is visible. Also, a missed call was shown in the activity feed even there was no ringing.

At first, I thought I could bring it down to cell phone calls only. But after asking my colleagues some users reported the same behaviour for calls coming from PBX systems.

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Missing Music on Hold for PSTN Calls on a Polycom VVX Phone

Some days ago I had a request from a customer about missing Music on Hold on Polycom VVX Phones and an Audiocodes SBC. The customer infrastructure:

  • Mixed Lync 2013 and Skype for Business  infrastructure on-premises
  • Audiocodes Mediant 2600 SBC
  • Enterprise SIP Trunk by Deutsche Telekom
  • 5.000 Users are enabled for Enterprise Voice features
  • Some are using Polycom VVX IP Phone (411 and 601)
  • Most users are using the Microsoft Skype for Business Client 2015 or C2R (2016)

The customer reported me, that for PSTN calls by Polycom VVX users the Music on Hold (MoH) was missing. When the same user calls someone in the company, the MoH is played to the other user. So, only PSTN calls are facing this issue. Furthermore, the customer told me that for users with Skype for Business softclient the problem doesn’t exist.

So,  in consequence it seems that we have to do a deeper look onto the Polycom VVX configuration because only these users are facing the problem. And only if the call was routed to or from the PSTN.

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