Auto Attendant DTMF Troubleshooting

This article outlines how to troubleshoot DTMF issues with an Auto Attendant.

• Office Manager Access to Manager Portal
• Access to a Call Trace

There are three DTMF transmission methods:

1. 1
   Inband (Audio)
2. 2
   SIP Info
3. 3
   RFC-2833 (via special RTP packets)

• The system can relay any DTMF method but only accepts RFC-2833 when acting as the DTMF endpoint (e.g., at an Auto Attendant).
• Recommended RFC-2833 Payload: 101
• Identifying DTMF Method & Payload: Check INVITEs and 200 OK responses in trace logs.

Identifying the DTMF Method

To locate the DTMF method in a trace:

1. 1

   Look for the "m" line and the following "a" lines.

2. 2

   For example, using RFC-2833 payload 101:

   m=audio 24190 RTP/AVP 18 0 101
   a=rtpmap:0 PCMU/8000
   a=rtpmap:18 G729/8000
   a=fmtp:18 annexb=no
   a=rtpmap:101 telephone-event/8000
   

   Here, the highlighted areas indicate the DTMF method as RFC-2833 payload 101.

   Here it is in the first INVITE of a Call Trace:

1. 1
   Carrier Not Using RFC-2833 Payload 101: Most carriers use RFC-2833 by default. If not, request the carrier to adjust their signaling to this payload.
2. 2
   Phone/ATA Not Using or Accepting RFC-2833 Payload 101:

   1. 1
      Review the phone or ATA’s administrative guide for DTMF configuration steps.
   2. 2
      Add the updated settings to the overrides and retry.
3. 3
   DTMF Fails Even with RFC-2833 Payload 101 Enabled:

   1. 1
      Test with an alternate carrier or different handset make/model to determine if the issue is specific to a device or carrier.
   2. 2
      If the issue persists, coordinate with support for further assistance.