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DTMF tones from iPhone not recognized in CUC auto-attendant

I've got a very intermittent issue where DTMF tones are not recognized by the auto-attendant in CUC (8.6.2). This of course stops the caller from being able to select any options or transfer anywhere within the system (until the timeout, when then transfer to the operator).

I cannot say with 100% certainty that the iPhone is at fault, but I can say that every case I've been asked to look into the caller has been using an iPhone 5, 5s or 5c.  I've investigated maybe 8 incidents over the past year.  Even those people who've complained about it find that the issue is intermittent with the issue happening in maybe 2 of 3 successive calls.

The inbound lines in our system are ISDN PRI through Windstream (on the old Cavalier network), terminating into a Cisco 2901.  Unfortunately I haven't  been able to debug the issue to capture the DTMF digits with an active caller yet, but next time it happens I'll give that a shot (debug voip vtsp session)   Unfortunately the caller today was a customer who didn't have time to indulge my desire to troubleshoot.


My question is whether anyone else has run into the issue?  If yes, how did you resolve it?   Also, are there any other debugs or logs I can look at to see what's happening behind the scenes?


Hello,Please include the


Please include the following details :-

1) Call flow

2) Is this issue seen for only pstn callers or internal callers as well?

3) What the full version of  CUCM , Unity connection , IOS version on the router ?

4) Is this problem seen with only IPhone 5 phones or other phones ?  

5) Please upload a "show ver" and "show run" from the IOS gateway?

6) what is the frequency of the problem you see ?



Karthik Sivaram


Which DTMF method have you

Which DTMF method have you configured ? In-band or out-band ?

 I saw kind of same issue on this forum in which user was facing intermittent DTMF problem on the IVR system. It was related one way audio on last call leg due to  RTP port blocking and as DTMF was configured In-Band , it was also not working. User was able to listen recorded messages but when asked to press digits it didn't capture it.




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