[Standards-JIG] Jingle: DTMF

Joe Beda jbeda at google.com
Wed Feb 15 17:31:10 UTC 2006

>From my quick research into the topic, it looks like there are two ways that
SIP does DTMF:
1) Over RTP w/ rfc2833
2) Over the signalling path with a custom cisco SIP extension (

If someone wants to connect to a SIP network (the most common way to connect
to the PSTN network and a major scenario behind DTMF) then you are dealing
with one of these cases:

1) Requiring DTMF to go over the signalling pathway will, in effect, require
the media to go via the same path as the signalling.  This is because the
gateway will have to interpret the media stream enough to hoist DTMF events
onto the signalling channel -- or if going the other way -- convert DTMF
signals to RTP packets.  This means that a service provider would have to
relay *all* media traffic.  This can add *significantly* to the bandwdith
cost of providing a SIP gateway.
2) Limit the types and numbers of PSTN service providers you can work with
because they may or may not support the cisco extension.  It isn't clear to
me how widely supported this extension is.

So -- in the interests of being pragmatic, we should support both ways of
doing DTMF.  In an ideal world we wouldn't have to do this two ways but we
don't live in an ideal world.

Support for RFC 2833 is signalled in jingle-audio by declaring support for
that 'payload-type''.  We should have another element under the jingle-audio
description to signify support for DTMF 'info' messages over the XMPP


On 2/15/06, Matthew O'Gorman <ogorman at gmail.com> wrote:
> this in my opinion is yet another reason not to do rfc2833 as jabber
> already provides a straight forward and reliable path for this data.
> On 2/15/06, Justin Karneges < justin-keyword-jabber.093179 at affinix.com>
> wrote:
> >
> > Hi,
> >
> > This is not true.  See XMPP-Core, Section 10:
> >
> > "Compliant server implementations MUST ensure in-order processing of XML
> > stanzas between any two entities."
> >
> > -Justin
> >
> > On Wednesday 15 February 2006 00:10, Jean-Louis Seguineau wrote:
> > > Simon, the simple answer to this is yes it is possible for stanza to
> > be out
> > > of order. XMPP does not 'guarantee' the ordered delivery of stanzas.
> > Even
> > > if they are in order most of the time, we should not assume it to be
> > always
> > > true.
> >
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