ARI - ChannelDtmfReceived event is not sent

Hi,
Using Asterisk 18.2.1
Using the default configuration to receive DTMF events as RTP out-of-band:

[transport-udp]
type=transport
protocol=udp
bind=0.0.0.0
external_signaling_address = x.x.x.x
external_media_address = x.x.x.x

[Phoneout]
type = endpoint
transport=transport-udp
allow= !all,ulaw,alaw
aors = AbcOutbound
direct_media=no
context=voice-otp
from_domain= x.x.x.x
send_rpid=yes
rtp_symmetric=yes
force_rport=yes
timers=no
outbound_auth = AbcDigestHeader

The problem: Our ARI application places calls to several different countries around the world. In some countries (UK, Germany) more than others we see that around 5% of the time users press the keypads to generate tones, our Asterisk server gets the RTP stream with those events, but our application does not receive a ChannelDtmfReceived event.

In a regular flow of execution we see the RTP events reaching the Asterisk server and the ChannelDtmfReceived event being sent to the app; In this case a DTMF 8 event was received.


We can see the associated events in the Asterisk log:

On other cases we see the DTMF RTP events coming in to the Asterisk servers but no ARI event being generated; In this case we would expect an event for DTMF digit 1:

Why does this happen? In the Asterisk logs we can see the duration of the DTMF received is between 60 and 300ms. When the duration is short usually there’s an “emulation” warning on the log, but the ARI events are generated. I do not see a pattern that would show when an ARI event is not generated…
Can it be that DTMF RTP events arrive out of order (udp) and this messes up the logic to generate the ARI event?
How can we improve the flow so Asterisk generates the ARI events more reliably?

Thanks for any suggestions

You’d need to enable Asterisk core debug logging[1] and DTMF logging to show what Asterisk is actually seeing. You should also ensure that you’re using the latest version of Asterisk, because I remember at least one DTMF fix involving timestamps for received DTMF.

[1] Collecting Debug Information - Asterisk Project - Asterisk Project Wiki

So we did enable core debug log using this
debug_log_123456 => notice,warning,error,debug,verbose,dtmf
CLI> core set verbose 5

*CLI> core set debug 5

*CLI> module reload logger

We see dtmf 3 coming into wireshark , but no events are generated in Asterisk for this. The dtmf 7 does generate ARI dtmf received event.
Both the dtmfs come in at the 18:26:17 marks, but I do not see any
res_rtp_asterisk.c – RTP creating Begin DTMF Frame
for dtmf 3 , but we do see it for dtmf 7.

Also I confirmed out asterisk version 18.2 has the timestamps fix for received DTMF. What could be causing asterisk to not react to some dtmfs (RTP Event, RFC).

This is wireshark for DTMF 7 , it is not allowing me to post all the images at once so posting them in different messages

This is the debug log for dtmf 7 , but did not see similar events for dtmf 3

Anyone has any update on why the dtmf is not getting sent to ARI.