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DTMF Issue in CUCM – MGW SIP Trunk


Looking for your kind advice,

Issue:  DTMF dialing (detection) not working on a SIP trunk between CUCM 6.1.x and an ITSP running the ZTE IMS Platform

Connectivity: Direct SIP trunk between CUCM to MGW (IMS) over  a WAN link

CUCM ver.

MGW: ZTE (Non Cisco)

Observation & Suspicious traffic: Some RTP Payload sending by CUCM could not be understood by MGW and the MGW discarding  the whole DTMF. Suspected RTP Payload snapshot is attached for reference. The ITSP is saying that they don’t support DTMF RTP events (inband) when they share the same timestamp with regular RTP packets (voice traffic).  That means the timestamp should not match for both, in effect CUCM should pause the regular media during the DTMF transmission. But we opened case with Cisco and they told us this is allowed by the RFC(s).


1,           1, Please advice what exactly the feature associated to the payload highlighted in the given screenshot, if so we could somehow disable it so that is not generated during our calls, to make the DTMF work…currently DTMF is intermittent and broken most of the time


              2, As mentioned above the RTP packets  and RTP events (DTMF) are using same timestamp and the  RTP  stream is sent in between RTP event packets,  ITSP/IMS guys are  also complaining about this behavior saying its again the RFC, so please suggest any solution to this issue.

Thanks in Advance

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