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Cisco Bug: CSCun87362 - PVDM2 Xcoder using incorrect RTP timestamp during and after a DTMF event

Last Modified

Jan 30, 2017

Products (1)

  • Cisco 3800 Series Integrated Services Routers

Known Affected Releases

28.3(10)DSP

Description (partial)

Symptom:
RTP timestamps in the media stream generated by a PVDM2 transcoder are incorrect during and after a DTMF event.

1) The RTP timestamps of all the event packets are only 80 (10ms) greater than the last audio packet. The timestamp value should have been incremented by the ptime. In our case 160 (20ms).

2) The first audio packet after the event has a timestamp that has only been incremented from the event timestamp by 160 (20ms). This timestamp value should have been incremented by the duration of the event. For example, if the duration of the event was 800 (100ms) the next g711 packet after the DTMF event should be incremented by 800 (100ms).

Conditions:
On an inbound call leg, DTMF events are being relayed via OOB signaling (SCCP/H323, etc) to CUCM and the outbound call leg is using inband RFC2833 (inband DTMF signaling) over the media stream. A transcoder is being used between the two call legs. For example:

        <------SCCP------>CUCM<------SIP------->
                           ^
IP_phone                  SCCP                  SBC<--SIP/RTP-->ITSP
                           v
        <--RTP/g729-->3845(Xcoder)<--RTP/g711-->


CUCM sends the SCCP message "SendDtmfTone" to the transcoder to inject a DTMF event into the media stream when it recieves a OOB DTMF digit on it's incoming call leg.
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