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DTMF RFC2833 and Out of Band on MGCP Gateway


Need some clarification and help understanding DTMF.for DTMF point of view, In my environment there are some 
devices working in rfc 2833 and some are on OOB (out of Band)method.

My secanrio would be Call-Agent--MGCP-GW(AS5350)

Since my gateway is controlled by Call Agent as mgcp and i wanted to use both mode(method) rfc 2833 and OOB(out of band), however i am not able to do so.

Is there way to configure it or to acheive.


VIP Mentor



You can only choose one method at a time with mgcp

RTR(config)#mgcp dtmf-relay voip codec all mode ?

  cisco        Set mgcp dtmf-relay mode to be cisco

  disabled     Set mgcp dtmf-relay mode to be disabled

  nse          Set mgcp dtmf-relay mode to be nse

  nte-ca       Set mgcp dtmf-relay mode to be nte-ca

  nte-gw       Set mgcp dtmf-relay mode to be nte-gw

  out-of-band  Set mgcp dtmf-relay mode to be out-of-band

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Hi, I have discovered this issue in my lab test environment too, but my SW MTP on CUCM gets invoked automatically when my SIP EX90 VTC, which uses RFC2833, makes successful calls over my MGCP GWY w/PRI.  The audio calls work fine, but the media flows from EX90 through the CUCM vs directly from EX90 EUD to the MGCP GWY.  Since Cisco 7975 phones support both In-Band and OOB DTMF, there is no such problem. Phones work great. No DTMF mismatch.

I don't want to use the SW MTP on CUCM, nor do I want to build a IOS HW or SW MTP on the GWY.  Therefore, I experimented with MGCP NSE, NTE-CA and NTE-GW since they support In Band DTMF. However the RTP Payload types need to be manually configured since they are not actually RFC2833 compliant.  I have looked online to see if there is a proven solution, but no luck so far.

I'm not working this effort full time, so I haven't completed working the problem.  I'm hoping I can set the MGCP RTP payload-type value to match the RTP payload type and finally get the MGCP GWY to support In Band DTMF.  If I can get that working, I can resolve the issue of having the SRTP media flow through a MTP.  This will be a more efficient flow.

Oh, almost forgot, the EX90 audio call works fine, but when the EX90 calls my remote CFB on the other side of the MGCP GWY, the DTMF digits fail to  reach the CFB.  PIN Code fails.  I haven't had time to sniff the packets yet, but I assume the MTP is being envoked just like it is on my other cluster, which I have used wire shark to capture the EX90 to CUCM/MTP flow.  I thought the DTMF should have been converted by the CUCM MTP since the media is flowing through the CUCM MTP. Weird.



Hi Rajeev,


You can use only one in MGCP gateway as rightly suggested by Ayodeji.

Also the Cisco IP Phone (SCCP) support both inband and out of band  DTMF.


If in your environment some device (non cisco sip endpoint) requires RFC2833 then MTP would be required to convert from inband to out of band and vice versa.

Kind Regards,