[VoiceOps] PRI loss/level settings - DTMF issues

Lee Riemer lriemer at bestline.net
Fri Mar 18 16:17:46 EDT 2011

Try lowering the audio gain.  Also, if you're running inband DTMF, try 
RFC2833, even while using ULAW.

On 3/18/2011 3:09 PM, Jay Hennigan wrote:
> On 3/18/11 12:30 PM, Lee Riemer wrote:
>> Are they in a room with echo dialing while on speakerphone?
> Sometimes, but I've been able to duplicate the failure on a handset.
> An analog phone on an FXS port on the Adtran works perfectly.
>> On 3/18/2011 1:32 PM, Jay Hennigan wrote:
>>> We are having some issues with doubled DTMF digits from a customer
>>> dialing into conference bridges, etc.
>>> Scenario: Shoretel PBX  ->   PRI ->   Adtran TA900 ->   SIP trunk.  We are
>>> using G711/RFC2833.
>>> The problem is intermittent, about 5% of calls or less, read-back of
>>> received digits shows occasional doubled digits, almost always DTMF "1".
>>> We were able to duplicate the issue with the Shoretel system going out a
>>> conventional TDM PRI as well, but the customer and the conferencing
>>> vendor and the customer tend to blame the problem on "the VoIP system".
>>>     It is very intermittent and DTMF works fine most of the time.
>>> The Shoretel itself sends only a short burst out the PRI regardless of
>>> the length of time the DTMF key is held.
>>> Comments from voice users on the receiving end are that the Shoretel
>>> caller's voice seems "hot".  The Adtran has settings to adjust level on
>>> FXS but not on PRI.  The Shoretel does have adjustments, presently set
>>> to 0 dB.
>>> It is my recollection from the old Bell/Mitel days that there should be
>>> padding on T1/PRI trunks but I can't find a spec.  From memory I want to
>>> say -6 transmit and -3 receive but Google is failing me on finding this
>>> documented.  Is there a standard loss/level best practice for this?
>>> The fact that the issue occasionally occurs on the TDM trunks leads me
>>> to think that the SIP RFC2833 conversion is not to blame and that
>>> perhaps there is acoustic coupling between the tone played out the
>>> phone's speaker being picked up by the microphone that padding would
>>> help.
>>> Any suggestions would be appreciated.
>>> -- 
>>> Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
>>> Impulse Internet Service  -  http://www.impulse.net/
>>> Your local telephone and internet company - 805 884-6323 - WB6RDV
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