Subject: RE: [AVT] Re: RFC 2833: Is there a way to handle tones with a dur ation over 8 a pproximately seconds?

From: "Prabhu, Raghavendra" <[email-masked]>
Date: Tue, 22 Oct 2002 16:42:25 -0700

If using approach (1) below, How do you distinguish between two same Events
like digit '1' in '911' with no (noticeable) gaps between the events ? If
bis-01 went with approach (1), implementations would(should ?) recognize
'91'.

-----Original Message-----
From: Henning Schulzrinne [mailto:[email-masked]]
Sent: Monday, October 21, 2002 1:11 PM
To: Paul Smith; [email-masked]
Subject: [AVT] Re: RFC 2833: Is there a way to handle tones with a
duration over 8 a pproximately seconds?

(Cc'ing AVT, for general input)

There are, I believe, two approaches:

(1) have two or more contiguous tones of 8 seconds each. You will be 
able able tell from the timestamps that there was no gap, i.e., that 
this is one tone instead of two;

(2) define a different, lower sampling rate for the event 'codec' if it 
is anticipated that tones could last longer than 8 seconds.

I'm adding wording on (1) to bis-01.

How common is this, btw?

Paul Smith wrote:

> Mr. Schulzrinne,
> Since a DTMF tone can last longer than 8 seconds: How should this be
> handled?
>
> >From RFC 2833:
> 3.5 Payload Format
> duration: Duration of this digit, in timestamp units. Thus, the event 
> began
> at the instant identified by the RTP timestamp and has so far lasted 
> as long
> as indicated by this parameter. The event may or may not have ended. For a
> sampling rate of 8000 Hz, this field is sufficient to express event
> durations of up to approximately 8 seconds.
> E: If set to a value of one, the "end" bit indicates that this packet
> contains the end of the event. Thus, the duration parameter above measures
> the complete duration of the event.
>
> Thank you for your time,
> Paul Smith

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt
_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

---

From: Henning Schulzrinne <[email-masked]>
Date: Tue, 22 Oct 2002 20:20:02 -0400

For real DTMF digits, there is a minimum interdigit spacing. I believe 
it's somewhere between 20 and 50 ms. Thus, such contiguous digits should 
never occur in the PSTN.