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

The basic question you raise is whether to set the E bit only at the end of the long event. I think that makes sense. The idea of the bit is to signal to the application that it's safe to hand the event to the next-higher layer. Clearly, this is a rare corner case, at least for DTMF. (It might occur for some of the line events.)

Prabhu, Raghavendra wrote:
Hi ,

I agree that this will not likely happen in the real world. However, the
reverse consequence maybe realistic. An example: Lets say a user wants to
dial '91' with legal interdigit spacing, the '1' lasting approx 16 secs at
8000Hz sampling rate.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| digit |E R| volume | duration |
| 9 |1 0| 10 | 1600 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| Interdigit time |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| digit |E R| volume | duration |
| 1 |1 0| 10 | 0xFFFF | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

| No gap |

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| digit |E R| volume | duration |
| 1 |1 0| 10 | 0xFFFF | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


According to approach (1), this should be deciphered as 2 events: '9'
followed by '1' since there was no gap between the two '1' events. To do
this, the receiving end should ignore the End bit (End bit means 'End of
event') when there is no gap between two events. Is this the general
understanding (or) should the E-bit not be set ?


Thanks
Raghavendra

-----Original Message-----
From: Henning Schulzrinne [mailto:hgs@cs.columbia.edu]
Sent: Tuesday, October 22, 2002 5:20 PM
To: Prabhu, Raghavendra
Cc: avt@ietf.org
Subject: Re: [AVT] Re: RFC 2833: Is there a way to handle tones with a
dur ation over 8 a pproximately seconds?


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.

Prabhu, Raghavendra wrote:

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:hgs@cs.columbia.edu]
Sent: Monday, October 21, 2002 1:11 PM
To: Paul Smith; avt@ietf.org
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
avt@ietf.org
https://www1.ietf.org/mailman/listinfo/avt
_______________________________________________
Audio/Video Transport Working Group
avt@ietf.org
https://www1.ietf.org/mailman/listinfo/avt



_______________________________________________
Audio/Video Transport Working Group
avt@ietf.org
https://www1.ietf.org/mailman/listinfo/avt