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DTMF


pbxuser911
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When calling into an Auto Attendant, several times Ive had this happen

i dial 2244 (Valid Extension on the system) when the Auto Attendant picks up, it tells me "this extension number does not exist"

i dial 2244 AGAIN and now it works

 

its almost like the PBX doesn't do anything with the DTMF

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Just checked the Wire Shark file (which i run against the PBX) and it shows the caller sent 44 then 2244. then you see multiple DTMF 1's,which i believe is when 2244 accepted the call on their cell phone, and pressed 1 to accept the call, but why so many 1's and why didn't it receive the first 22?

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There are many buggy RFC2833 (now RFC4733) implementations. I assume that when you look into the wireshark either the two "2" are glued together or there is no DTMF at all. Sometimes providers signal they they would support out of band in the SDP, then when the media arrives it is inband.

 

I had the same issue where the SIP trunking provider changed me over to another SIP registration proxy due to DTMF issues (different implementation apparently). Once on the newer proxy the problem went away. Sounds very similar to what I had issues with.

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  • 2 weeks later...
so you believe you had the issues with the SIP Provider? and its not related to the PBX?

 

It's certainly a possibility. I kept looking at everything on the PBX and handset side and once I verified it was and looked ok put in a ticket with the carrier who assisted in the troubleshooting process and found the problem to be on the trunking server I was connecting to (though it had been working for some time before that). They made some changes apparently, I was moved to another primary and secondary and the problem went away and has been fine since.

 

I only had the issue with one of the trunking providers. Do you have multiple providers that this is a problem with? Worth a try asking the provider.

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  • 1 month later...
Does it make a difference if you wait a little? maybe the problem is that the call is not connected yet.

We run an IVR hosting service and we sometimes have customers complain about lost DTMF. Our lines are good ol' TDM T1s split off of channelized DS3s from our carriers, so I'm certain we're not losing digits from the carrier. However, invariably, when we ask the customer having issues whether they're using SIP phones, they say, "yeah, is there a problem with that?" Much of the time those digits are being dropped between the SIP phone and the SIP PBX. UDP is nowhere near reliable enough -- even on a LAN -- especially for discrete data like key presses. Your brain can compensate for a lost packet or two causing jitter. Your PBX can't compensate for a DTMF packet that never reaches it.

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We run an IVR hosting service and we sometimes have customers complain about lost DTMF. Our lines are good ol' TDM T1s split off of channelized DS3s from our carriers, so I'm certain we're not losing digits from the carrier. However, invariably, when we ask the customer having issues whether they're using SIP phones, they say, "yeah, is there a problem with that?" Much of the time those digits are being dropped between the SIP phone and the SIP PBX. UDP is nowhere near reliable enough -- even on a LAN -- especially for discrete data like key presses. Your brain can compensate for a lost packet or two causing jitter. Your PBX can't compensate for a DTMF packet that never reaches it.

 

Well, there is a lot of buggy RFC4733 implementation out there, that's for sure. Packet loss should not cause any double-digit detection there, out of band is very robust against packet loss.

 

Usually the problem comes from "DTMF transcoding". Especially when using TDM lines, someone has to translate inband into out of band that usually leaves a small detection ap on the edges where there is still inband DTMF.

 

---------IIIIIOOOOOOOOOOOOOOOOOOOOOOOOOOOIIII------------------- (try to read it aloud)

 

The whole thing is a tricky topic. I remember we had a discussion years before and the conclusion was that the conversion from inband to out of band should be avoided whenever possible. I think that was the point when we added inband detection to the PBX.

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