MGCP and dtmf-relay

[chris.damore]

We have a customer site that is having some issues with their IVR system. The system worked without any issues for a couple of months. We had to change the gateway from H.323 to MGCP because of a caller ID issue. As soon as we made the change to MGCP, the IVR system started periodically receiving duplicate digits when a customer dials in their account number. The IVR system is connected to the IPT network via ATA’s. We’ve replaced ATA’s, but the problem persists. We’ve tried several different dtmf-relay commands, still does the same thing. A TAC case was opened and debugs sent to Cisco. TAC says the ATA’s aren’t sending any dialed digits twice.

My question is, why would this break after changing the gateway router from H.323 to MGCP????

The gateway is connected to the PSTN via a PRI.

Any help given would be greatly appreciated!

Thank you,

Chris

[jbouwkamp]

Have you hooked up an analog phone to the ATA and actually listened to what DTMF is being sent when someone on PRI presses keys? You should be able to audibly hear if its sending it once or twice when the PRI caller only presses a key once.

I would also investigate if the length of the DTMF tone is different with MGCP vs H323 when sent out of band. It is possible that the IVR system is hearing a LONG dtmf key press and considering it two tones. Can you tweak anything regarding DTMF on the IVR to allow for longer DTMF tones?

I don't know if any of these suggestions are relevent but it is what I would investigate if I had tried all the MGCP dtmf relay commands.

[chris.damore]

This issue is very sporadic, so no, we haven’t been able to hook an analog phone up and listen to the tones.

Where would I look to see if the length of the DTMF tone is different with MGCP vs H323?

Thank you very much!

Chris

[jerald.love · Accepted solution]

We're running into a similair issue and TAC DE is currently testing a fix, you should open a TAC case to confirm.

(CSCsc19202 Bug Details

Symptoms : DTMF digits may not get recognized by your IVR system. If you

listen carefully for the

DTMF tone that is sent by gw, you may hear doubl sound.

Condition : GW is a MGCP gw which has configured with mgcp dtmf-relay voip

codec all mode out-of-

band or no mgcp dtmf voip, and codec g711u is used.

Workaround : Use codec g729 to make the in band dtmf unrecognizable.)

[chris.damore]

Thank you very much for your reply!!

How would I configure DTMF-Relay to use g729?

Thank you again!

Chris

[shane]

Did anyone ever figure out how to configure DTMF-Relay to use g729?

[anup.anand]

I think what the bug workaround says is to enable G729 codec for the call and due to the compression of g729, the inband DTMF will be unrecognizable. There is no configuration to enable DTMF relay to use G729.

Regards,

Anup