Telephone dial tones not recognised by remote PABX

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Phazir50

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#306249 8-Jul-2023 01:13

When I phone my doctor's surgery I get the ubiquitous 'Press 1 for abc, press 2 for xyz', etc. If I am using my mobile phone, this process works as expected, but if I use my portable DECT phone the PABX happily ignores my key presses and drones on with its menu. The problem does not occur with any other phone number answered by a PABX. What might be the cause of this intriguing issue?
Equipment: Pamasonic DECT phone connected to an AVM FritzBox modem using fibre Broadband telephony.

Phazir50

Zeusssy

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#3101136 8-Jul-2023 02:08

Without knowing specifics, and having traces run to confirm...

Its probably in-band DTMF vs RFC2833 in-band DTMF telephone event. So the likely two SIP endpoints are talking to each other in different 'languages' when it comes to DTMF or your button pressing.

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BarTender

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#3101143 8-Jul-2023 06:35

I expect if you tried with a mobile phone to call the number and most likely it should work. As Zeusssy said what will be happening is it will be DTMF encoding and probably because it’s sip to sip and you are using a FXO adapter aka your Fritxbox then your fritxbox isn’t encoding RFC2833 when the call is established.
Here is Poly talking about it
https://community.poly.com/t5/VoIP-SIP-Phones/FAQ-Phone-unable-to-send-DTMF-to-an-IVR-system-or-how-to/td-p/4237

MadEngineer

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#3101149 8-Jul-2023 07:49

Call a third phone that you can answer from your mobile and press one of the numbers a few times. Record it if you can’t remember a tone.

Repeat the same from that DECT phone and compare the tones.

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raytaylor

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#3101167 8-Jul-2023 09:21

I'll explain a little further....

When you are using voip, the call is encoded into a compressed audio format. The sound quality drops a little bit.

When your dect phone sends an analog DTMF tone, it then goes through the encoder inside the router/ATA and converted to the compressed audio format.
However like a low-bitrate mp3 file, the sound doesnt get accurately reproduced at the other end - there are slight differences in the sound of the audio which for speech is okay, but when tones need to meet certain frequency criteria, will not match what the other end is listening for. Eg. the IVM system isnt detecting you are pressing 1,2,3 because the sound of the tone when it arrives doesnt exactly match the specifications for a 1,2,3 tone. The sound is slightly lower or higher than it should be.

To combat this, the router or ATA will have an option called RFC-2833.

If the ATA detects that you are sending a DTMF tone down the line, rather than convert it to the digital audio, it constantly listens for the tones, stops the audio and sends a command instead.
"User pressed 3"

At the other end while converting the digital audio to analog, the recieving ATA will follow the command by stopping the digital audio stream playback and instead generates the correct DTMF tone of the correct specification, then continues to play the audio.

There are a couple of reasons why in-band tones are still used. Alarm systems calling into a monitoring centre is one of them. Alarm systems use more simplistic tones to communicate commands and reports, while also having a much larger index of tones that dont match any of the 1-9,ABCD of the official DTMF standard. The alarm system tones will also handle being sent through a digital audio compressor much easier.

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old3eyes

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#3101231 8-Jul-2023 12:19

In the years I worked on PBX systems with SIP trunks I only ever found one NZ carrier that used inband DTMF the rest use RFC-2833.

Regards,

Old3eyes

Phazir50

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#3101567 8-Jul-2023 21:44

Thanks everyone for the replies. I am not in any way able to comprehend some of the answers, but I did find some references to DTMF and RFC2833 in the modems config file. I should clarify details of my set up. I have an NF18ACV as the master router with the FritzBox as a slave. The reason for this is that the FritzBox is much easier to configure, for all my network needs, than the NF modem. The issue exists with the phone's base unit connected to either modem. I was able to extract the configuration details for the NF modem and the lines referring to DTMF, RFC2833 and SIP are as follows:
<VoiceProfile instance="1">
<Enable>Enabled</Enable>
<MaxSessions>6</MaxSessions>
<DTMFMethod>RFC2833</DTMFMethod>
<Region>NZ</Region>
<DigitMap>[2-9]xxxxxx|0[34679]xxxxxxx|0[589]0[08]xxxxxx|0[02]x.|08[1-689]x.|087[0-8]x.|0879[0-9]|05[1-9]x.|1xx|1xxx|7xx|#x.|01x.|909|606|*xx.</DigitMap>
<BREAK_MIN_DURATION>40</BREAK_MIN_DURATION>
<BREAK_MAX_DURATION>140</BREAK_MAX_DURATION>
<FXSLS_SEIZE_DETECT>300</FXSLS_SEIZE_DETECT>
<X_BROADCOM_COM_DtmfRelayPayload>101</X_BROADCOM_COM_DtmfRelayPayload>
<PbxInsideDigitmap>[0-8]xxx</PbxInsideDigitmap>
<CallIdFskAppendChar>$</CallIdFskAppendChar>
<UaHeaderInfo>NF18ACV-Contact</UaHeaderInfo>
<SIP>
<ProxyServer>voice.vibecom.co.nz</ProxyServer>
<RegistrarServer>voice.vibecom.co.nz</RegistrarServer>
<OutboundProxy>voice.vibecom.co.nz</OutboundProxy>
<RegisterExpires>300</RegisterExpires>
<DSCPMark>18</DSCPMark>
<OutBoundListBakForVTP>UDP:fqdn:voice.vibecom.co.nz:5060</OutBoundListBakForVTP>
<X_CT-COM_Standby-RegistrarServerTransport>UDP</X_CT-COM_Standby-RegistrarServerTransport>
<X_BROADCOM_COM_SessExpireTimer>36000</X_BROADCOM_COM_SessExpireTimer>
<CallReturnActkey>*69</CallReturnActkey>
<DndActkey>*78</DndActkey>
<DndDeactlkey>*79</DndDeactlkey>
<AnonBlockActlkey>*77</AnonBlockActlkey>
<AnonBlockDeactlkey>*87</AnonBlockDeactlkey>
<CallTrsfActkey>#90</CallTrsfActkey>
<CallTrsfconActkey>#91</CallTrsfconActkey>
<CallWaitDeactkey>*70</CallWaitDeactkey>
<AnonCallActlkey>*67</AnonCallActlkey>
<AnonCallDeactlkey>*82</AnonCallDeactlkey>
<CallFwdUnconActkey>*72</CallFwdUnconActkey>
<CallFwdBusyActkey>*74</CallFwdBusyActkey>
<CallFwdNoansActkey>*75</CallFwdNoansActkey>
<CallFwdUnconDeactkey>*92</CallFwdUnconDeactkey>
<CallFwdBusyDeactkey>*94</CallFwdBusyDeactkey>
<CallFwdNoansDeactkey>*95</CallFwdNoansDeactkey>
<CallFwdDeactkey>*73</CallFwdDeactkey>
</SIP>
I will work my way through all that is in the replies thus far and try the suggestions made.

Thanks

Phazir50

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Bung

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#3101574 8-Jul-2023 22:42

Phazir50:
When I phone my doctor's surgery I get the ubiquitous 'Press 1 for abc, press 2 for xyz', etc. If I am using my mobile phone, this process works as expected, but if I use my portable DECT phone the PABX happily ignores my key presses and drones on with its menu.

The problem does not occur with any other phone number answered by a PABX.

If you don't have a problem with other numbers perhaps you should ask your doctor's reception if they have a new system and have any other callers had the same problem before changing your system. The problem could be theirs.

coffeebaron

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#3101577 8-Jul-2023 23:13

Please explain more your master / slave setup with your routers? Are you just using the Fritz as an ATA?

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