[Freeswitch-users] Is RFC 4733 supported ?

Richard Lamkin Richard.Lamkin at mettoni.com
Fri Apr 24 03:18:39 PDT 2009

Thank you all for your contributions to this thread. 


If I understood correctly.

All DTMF signals defined in RFC4733 are supported, and similarly they
are supported to RFC2833.  There are other signals defined in RFC4733
that are not implemented.


The note from Michael "strict in what we send and loose in what we
accept" is a useful clarification. 




Richard Lamkin

Mettoni Group

richard.lamkin at mettoni.com 



From: Arsen Chaloyan [mailto:achaloyan at yahoo.com] 
Sent: 23 April 2009 19:50
To: freeswitch-users at lists.freeswitch.org
Subject: Re: [Freeswitch-users] Is RFC 4733 supported ?


> I should clarify that we support the dtmf tones plus flash but no
other tones at this time.

Seems you have not to support other tones, because they are declared as
deprecated in RFC4733 (See also a companion RFC4734). Flash is
deprecated either, however supporting flash ensures backward
compatibility. Anyway it's used only by a few gateways. 

RFC 2833 caused me a lot of headaches in the past, there were 13 drafts
over 2833, if I'm not mistaken, before they finally published 4733.
It indeed contains some clarifications, while it's mostly backward
compatible with 2833.
The most ridiculous part in out of band implementation is robustness
against network conditions and interference of in-band and out-of-band
tones (SIP -> PSTN) , surely not counting robustness against broken
implementations (from Asterisk 1.2 times).

Anyway, section " Playout of Tone Events in RFC4733" deserves
careful reading.


Date: Thu, 23 Apr 2009 11:48:39 -0400
From: Michael Jerris <mike at jerris.com>
Subject: Re: [Freeswitch-users] Is RFC 4733 supported ?
To: freeswitch-users at lists.freeswitch.org
Message-ID: <909FF661-266E-47D1-A881-52D54C99ACCB at jerris.com>
Content-Type: text/plain; charset=US-ASCII; format=flowed; delsp=yes

I should clarify that we support the dtmf tones plus flash but no  
other tones at this time.


On Apr 23, 2009, at 11:17 AM, Steve Underwood wrote:

> Michael Jerris wrote:
>> rfc 4733 attempts (and fails miserably) to clarify rfc2833.  It
>> doesn't "really" change anything of any real substnace.  Our handling
>> of these packets tries very hard to be strict in what we send and
>> loose in what we accept and we tend to interoperate pretty well with
>> most endpoints.  That being said, there are some very broken  
>> endpoints
>> out there (such as sonus) that require special hacks, some are
>> automatic, some require settings.  All that being said, we should be
>> very compliant with both 2833 and 4733, although you will generally
>> see references in settings refer to 2833.
> RFC4733 largely tries to clarify RFC2833 for the DTMF features.  
> However,
> for most other signal it is very incompatible with RFC2833.

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