Issue with DTMF While in Conference Call

I am currently investigating an issue I have internally, and have heard someone else having on the Technet forums:


The issue is that when in a communicator conference call, you cannot send DTMF tones to a PSTN participant. The scenario is as follows:

  1. Communicator call, or communicator conference call is initiated
  2. User invites a PSTN number to that conference call
  3. PSTN number requires DTMF tones, whether it is a conference bridge, or an attendant menu, could be various situations
  4. No DTMF is received by the PSTN number.

So far, I have been able to confirm a couple of things. This happens with CS2010 as well as OCS 2007 R2. Internally we use a Dialogic DMG2120 gateway, and I have confirmed that I do not see DTMF on the gateway’s SIP side from OCS.

I am using this post to hopefully get some partners and customers to try this scenario, and see if they have the same issue. I would find it hard to believe that this is a bug in OCS/CS2010 that Microsoft has not addressed, but I am hoping to find a common configuration among people experiencing this issue so we can maybe narrow it down.

Typically this is a gateway issue, however like I said, I have not seen any DTMF come from OCS to the gateway when in the conference call.

Please respond in the comments with a brief description of your OCS setup and gateway/SIP trunk, and if you experience this issue or not.




That was quick!;en-us;2254369&sd=rss&spid=12605

It is identified in the above article. AVMCU does not support DTMF Relay. Thanks to the commenter!


About Randy Wintle

Unified Communications Architect

Posted on July 13, 2010, in Audio/Video MCU, Communications Server 2010, Conferencing, Dialogic, Enterprise Voice, OCS 2007 R2, Unified Communications and tagged , , , , , . Bookmark the permalink. 7 Comments.

  1. I found this some months ago… I use Audiocodes GW but this happens with any gateway because the thing is on avmcu.

  2. I have same issue with r2 and current w14 beta.

    It dose not send dial tone in r2 I was told this will work in w14 might be in the w14 refresh coming July 16 I will post my results.

    • Hi Keith,

      Did the Wave 14 refresh fix this. I hane an enquiring mind and i would like to know.


      • Nope, still not activated on the AVMCU.

        I will poke around and see if I can find out “why” not just that it doesn’t work.

  3. This has had me vexed for 2 years. Glad to see MSFT finally made a public statement. Really defeats the purpose of adding people to a call already in session. We had tried it iwth multiple gateways and providers. I can’t tell you how many times i have said. Hey — hang up i’ll call you back after I get so and so on the line. Many companies use an auto-attendent / IVR to reach people. You would think that passing DTMS in a conference would be a no brainer. Thanks so much for the posting with the link to the rather lame MSFT response.

  4. Glad MS finally went public too! We called MS support for this issue in Feb of 09 during our R2 rollout and were told at that time that no SP or udpates to R2 would have a fix and that we would have to wait for Wave 14…guess he meant 15 🙂

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