Subject: RE: Additional Info on DTMF under SIP

From: "Fox, Mike" <[email-masked]>
Date: Thu, 11 Nov 1999 18:20:34 -0800

> From: Dean Willis [mailto:[email-masked]]
...
> Why does MGCP use media signals rather than just passing the 
> RTP up to the
> softswitch?
> 
> Answer: because signaling is not the same as media. Passing 
> the RTP upstream
> would require splitting off the tones RTP stream, forking it, 
> and proxying
> it numerous times along the control path. Messy and awkward.
>
This cuts both ways. INFO messages must be forwarded, avt-tones can be
forked or forwarded. Forwarded information may cross proxies who do not care
about their content. Forked information is only sent to the interested
listeners. In general, forked information will arrive at all the listeners
of a proxy chain more quickly than forwarded messages. The avt-tones method
leaves the implementation with a choice, INFO messages do not.
> 
> Thinking of a softswitch as an enhancd services platform is a 
> vey limited
> approach. I visualize the current round of softswitch products as
> large-scale media gateway controllers and telephony signaling 
> gateways that
> adapt from GSTN to SIP. Enhanced services can then be built 
> very simply on
> general purpose computers using the same SIP interface to the 
> softswitch
> that softswitches use between themselves. These enhanced 
> services often
> don't need to be anywhere near the media path.
> 
I do not think about avt-tones as only a media stream. It has duality, with
both good media and good signalling characteristics. It is up to the
receiver as to what property it wants from it.

Best regards,
Mike Fox

---

From: "Pete Cordell" <[email-masked]>
Date: Fri, 12 Nov 1999 13:17:59 -0000

I just wanted to ask whether the issues of feature interaction have been
addressed here?  For example, I might be connected to a service that
provides toll by-pass and uses DTMF to control follow-on calls etc.  One of
the calls I make might be to the (now standard) banking service.  In this
case the two systems may interpret the commands in a different way, and
indeed do the interpretation at the same time.  Does this need to be
addressed?  (My understanding of some of the schemes proposed is that the
RTP DTMF sender would send the RTP packets to all entities that had
indicated that they want DTMF info.  This would cause a lot of feature
interaction problems.)

BTW, I do think that any banking system that doesn't allow for unintended
double key hits, or mis-detection of key hits is a bad UI system.  I mis-key
all the time.  Intermittent noise can also cause false detections.  I would
advise changing banking providers in this case!!!

Pete

=============================================
Pete Cordell
[email-masked]
=============================================

---

From: "Pete Cordell" <[email-masked]>
Date: Fri, 12 Nov 1999 13:03:51 -0000

Just for the record, as here, IMTC VoIP came to the conclusion that there
was probably a need for both schemes, and RTP based DTMF signalling was not
favoured over a signalling path equivalent.  The VoIP doc goes on about the
RTP method more than the control plane method because the H.323 docs already
covered off the control plane method, but did not include much (anything?)
on the RTP method.  (Also the original editors of the VoIP doc were very
into DTMF over RTP, so that in itself favoured the RTP approach also!!!  But
not unfairly of course  as none of us would do that!!!)

Pete

-----Original Message-----
From: Fox, Mike <[email-masked]>
To: Dean Willis <[email-masked]>; Jean-Hugues ROBERT <[email-masked]>;
Michael Thomas <[email-masked]>; Gregory D. Girard <[email-masked]>
Cc: [email-masked] <[email-masked]>;
Dye, Robert <[email-masked]>
Date: 11 November 1999 01:18
Subject: RE: Additional Info on DTMF under SIP

>
>The idea, posted earlier, that the H.323 group has looked into this issue
is
>correct. The avt-tones draft is in part the result of the IMTC VOIP work,
>and the agreement of H.323 implementers in this IMTC forum that a rtp
>signalling mechanism is the preferred method to propagate DTMF/signalling
>information. The recommendation of the IMTC VOIP IA is to use a rtp-dtmf
>signalling method when one becomes available.
>