RE: DTMF timing (was Re: [Sip] INFO ...)

["Eric Burger" <[e-mail]>]

Review KPML and the Application Interaction Framework.

RTP (RFC 4733/2833) is for the *timely*, _unreliable_, delivery of
TONES.

SIP (RFC 4730) is for the _reliable_, *soon-enough*, delivery of
SIGNALING.

Please don't confuse signaling with tones.  Sometimes, we do use tones
for signaling.  That was from the days of analog transmission of user
input.  We have moved beyond that, one hopes...
 

-----Original Message-----
From: Hadriel Kaplan [mailto:[e-mail]] 
Sent: Thursday, November 01, 2007 6:15 PM
To: Dean Willis; Michael Procter
Cc: [e-mail]
Subject: RE: DTMF timing (was Re: [Sip] INFO ...)



> -----Original Message-----
> From: Dean Willis [mailto:[e-mail]]
>
> On Nov 1, 2007, at 3:20 PM, Michael Procter wrote:
>
> > Whilst having the RFC2833 arriving in the timestamped audio stream 
> > is certainly beneficial, it is also true to say that the RTP stream 
> > generally travels quicker than signalling.  One of the main reasons 
> > for this is that the RTP usually travels point-to-point, whilst the 
> > signalling path often includes a couple of proxies.  Even if the 
> > proxies process the messages in zero time (which they don't), there 
> > are still multiple network hops introduced as a consequence.
> > Additional delays incurred by the proxies/other intermediate 
> > signalling elements swiftly add up too.
>
> I agree that this sounds correct in theory.
>
> What I'm wondering about is those deployments that use media-path 
> control elements (aka SBCs that police media) and/or decoupled media 
> and signaling processors.
>
> I suspect that that SBCs slow down RTP about as much as they slow down

> SIP. COuld be more, could be less -- I don't really know.

Uh, nope.  There are such things as software-based SBCs, for enterprises
and such, but most of the provider ones use dedicated hardware to handle
RTP/RTCP. (using NPs/ASICS/whatever)  It's not discernibly slower than a
router, depending on the vendor.


> We don't really use DTMF much between "traditional SIP endpoints" -- 
> the kind of all-in-one device that does everything in a dedicated 
> general-purpose processor. It seems that in practice we use it more 
> frequently in transactions that involve large-scale decoupled gateways

> and decoupled media servers, at least at one end of the call. I 
> wouldn't be surprised to see the practical reality collide with the 
> theory around 2833.

Yeah, I buy that.
My worry though isn't about speed.  It's about use.  One of the obvious
use cases for signaling-based DTMF is it follows the signaling, and the
media doesn't need to.  For an info-dtmf model, that essentially means
something in the middle that wants dtmf (an app-server, for example) has
to act as a b2bua for signaling, but doesn't need to be in the media
path.  So even if both info-dtmf and 2833 get negotiated, you'd want to
use the info-dtmf.  Although I guess if the app-server needed it that
way, it would have to have removed 2833 from SDP (yuck), 'cause
otherwise as a UA it's essentially lying by offering 2833.

-hadriel



_______________________________________________
Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol Use
[e-mail] for questions on current sip Use
[e-mail] for new developments on the application of sip

Notice:  This email message, together with any attachments, may contain information  of  BEA Systems,  Inc.,  its subsidiaries  and  affiliated entities,  that may be confidential,  proprietary,  copyrighted  and/or legally privileged, and is intended solely for the use of the individual or entity named in this message. If you are not the intended recipient, and have received this message in error, please immediately return this by email and then delete it.


_______________________________________________
Sip mailing list  https://www1.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use [e-mail] for questions on current sip
Use [e-mail] for new developments on the application of sip