IOS Router with H323 and SIP-Trunk for 3rd Party Callcenter

Unanswered Question
May 30th, 2009


We are using an IOS 2811 Router with 12.4.15T8 as H323 Gateway. Further we use an 3rd Party Callcenter conected via SIP Trunk to CUCM 6.1.2-1125.

Incoming Calls on the h323 Gateway connect to the CUCM. The call is routed to a SIP-Tunk.

The RTP only works when an MTP is used because of DTMF Problems.

The SIP-Trunk is configured with RFC 2833 for DTMF relay.

We do not want to use an MTP. What must be configured?

I have this problem too.
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gogasca Sun, 05/31/2009 - 00:19

Dial peers SIP to cucm r configured with proper RFC 2833 for dtmf-relay?

whats the terminating device in cucm?

Florian Kroessbacher Fri, 06/05/2009 - 13:33


The Call goes that way

PSTN -> Cisco 2811 -> H.323 to CuCM -> SIP Trunk to Callcenter

The RTP shoud directly Connect the GW and the Callcenter. But there must be a MTP for an Working connection

cheers Floh

Nicholas Matthews Fri, 06/05/2009 - 16:00

You must configure RFC 2833 (rtp-nte) on your H323 dial peers on the 2811, that way it isn't necessary for DTMF.


martin1.plank Sat, 06/06/2009 - 03:48

Hi Nick,

I've configured:

dial-peer voice 1 voip

session-target ipv4:

dtmf-relay rtp-nte

But the MTP is still used!

parshah Sun, 06/07/2009 - 12:47


From the call flow that you have given,

PSTN -> Cisco 2811 -> H.323 to CuCM -> SIP Trunk to Callcenter

RTP should connect directly between 2811 and the Call Center. Now, MTP will be put in between if the 2 ends don't have similar capabilities. Most likely in this case DTMF mis-match.

What you need to confirm is whether the Call Center side does RFC 2833 or not? You have configured rtp-nte on the IOS and MTP is getting allocated by CUCM, I would guess its because Call Center app needs DTMF OOB and not RFC 2833.

parshah Mon, 06/08/2009 - 10:31

Can you please elaborate? Not sure what yes refers to?


Florian Kroessbacher Mon, 06/08/2009 - 11:22

We are getting a new Version of the Callcenter app!

there we should have the choose of

OOB or 2833 or both so we can specify what the Server will reply in his sdp

when we patched the callcenter we should troubleshoot again i think

cheers Floh

Florian Kroessbacher Tue, 06/09/2009 - 11:02

Hy Out There!

now we updated the Callcenter Software -> now we can choose only RFC 2833 (no OOB) so there won't be a MTP (or XCODE) inserted within the call -> so the Problem is gone (with G.711 & G.729)

I want to thank all the quys on NETPro for helps etc.

cheers Floh


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