Handling DTMF in the RTP Payload

As mentioned above, Vocera SIP Telephony Gateway supports DTMF events as RTP payload as specified by RFC 2833.

If your IP PBX does not handle DTMF events as RTP payload and you do not use a media termination point (MTP) to convert out-of-band SIP Notify DTMF messages into RFC 2833 in-band (RTP), Vocera recommends that you connect to the PBX via a T1 ISDN-PRI circuit. This would connect to a media gateway (such as a Dialogic Media Gateway), and then to the Vocera SIP Telephony Gateway, as shown in the following figure.

Figure 1. VSTG connecting to PBX through Dialogic Media Gateway

To test whether your PBX handles DTMF in the RTP payload, connect a SIP softphone (such as x-lite, which you can download at http://www.counterpath.com/x-lite.html) to the PBX. To test outbound DTMF, attempt to use an outside service that uses DTMF, such as a paging service. To test inbound DTMF, use the SIP softphone to call your cell phone. Press some DTMF keys on the cell phone while you listen on the SIP softphone. If you can hear the DTMF tones, then they are NOT being converted correctly via RFC 2833.