SNOM D3xx phones and DTMF

[Bert Van de Casteele]

Hello,

first and foremost - apologies if this has been answered before. I've searched the forum several times now and have found some threads that might be helpful, but none of the suggestions seem to work. I would be much obliged if someone could point me in the right direction.

Now on to the problem :

We use 3cx with a local SIP provider (trunk). Several days ago some of my colleagues downstairs started complaining that, whenever they called to a number that used a digital receptionist ("press 1 for sales", etc....) they could do nothing.

Since then I've found out that for softphones (windows Clients, mobile app) I only needed to change the DTMF setting from RFC XXXX(sorry, number escapes me now) to In-Band. Since that change, all sofrphones have resumed working with DTMF.

However, we also have some hardphones - SNOM D3XX models. It seems that whatever I do, I cannot get the DTMF going on those phones :

1) updated phones to newest firmware (6.88)
2) in Phone UI - set DTMF to SIP INFO (on and SIP INFO ONLY - does not make difference)
3) downloaded newest 3cx SNOM D3XX templates
4) looked around in "Phone Provisioning" to look for an identical option as for the softphones - no dice.

I'm running out of ideas ATM. What I am planning to do is an update for 3cx itself (minor update, but still), shutting down and restarting the server, factory resetting and reprovisioning all phones (again, I already did that), etc...

Has anyone had any experience with these particular brand of phones and if so, how were you able to resolve that issue?

As always, thanks in advance,

 

[leejor]

If you changed the DTMF method to In-Band, then it suggests the set is sending DTMF audio, not SIP-Info. If that works for you, great...however, your VoIP provider should accept one of the out-of-band methods as well (ask them), which (in theory) should be more reliable.

In many devices, there is an "Auto" DTMF setting, which, if available, I've found to be the best choice in most instances.

 

[YiannisH_3CX]

Hello @Bert Van de Casteele

As i understand it the issue was with all devices using DTMF method RFC2833. If that was the case i would recommend contacting the provider and asking them what do they support for DTMF. If they do not support RFC2833 then i would recommend switching to a supported provider to avoid issues in the future. https://www.3cx.com/partners/sip-trunks/

 

[eddv123]

I would concur with YiannisH, RFC 2833 should definitely be supported (this is commonly what it is known as but has had updated versions such as RFC 4733).

Standard or Classic INBAND DTMF should not be an option for provider or handset, this method places the DTMF digits in the actual RTP stream (where RFC 2833) uses its own stream.

I know you will find this method supported in Yealinks (not sure about snoms) but your provider should not be using this as a compression codec would render these tones useless as they are carried with the compressed RTP traffic.

SIP INFO where an alternate option can offer synchronization issues as packets take a completely different path (via SIP server) instead of in the media flow.

 

[Bert Van de Casteele]

Thanks all for suggestions, I'll contact provider and my reseller,

I'll keep you posted