Hi Guillermo,
Please read through RFC 2833 especially section "3.5 Payload Format."
In practice we have found that there are many variations used for RFC 2833
(telephone-event) DTMF generation in RTP.
We have also found there are many variations in the way a device (e.g., ATA)
will interpret received RTP telephone event packets to generate DTMF signals on
the analog port.
Most issues we have observed are due to improper setting (or not setting!) of
the DTMF event end bit.
Also issues arise when not correctly interpreting the "duration" field when
generating the RFC 2833 RTP event.
The duration field is in "Timestamp Units" which means it is based on the audio
sampling rate for the audio codec in use.
This is often 8000 Hz.
For an 8000 Hz audio sampling rate, to generate a 100 ms DTMF signal, the
duration field would need to be 8000 X 0.1 = 800.
I noticed in your examples:
Functioning DTMF: Duration= 1200 (if 8000 Hz sampling then this is 1200/8000 =
150 ms.
Non-Functioning DTMF: Duration= 960 (if 8000 Hz sampling then this is 960/8000
= 120 ms.
Most CO type DTMF receivers should detect DTMF as short as 60 ms so if the
duration is the problem then:
1) The DTMF receiver in use requires a longer than 120 ms DTMF signal for
detection.
OR
2) The device that is receiving the RTP DTMF event packets is not generating
the analog DTMF signal for the specified duration.
OR
3) The sampling rate is not 8000 Hz but perhaps 16000 Hz (for example for
wideband audio) which would make the RTP durations half as long (75 ms (pass)
and 60 ms (fail).
We have found that the volume parameter has not been used for most of the
devices we have tested and instead the device generating the analog DTMF just
uses a fixed amplitude.
You can capture the DTMF on the analog line and measure the duration, levels,
etc.
See: www.tsa6000.com for one device that can do this (and much more).
I hope this helps!
Sincerely,
///////////////////////////////////////////////////
James R. Bress
AST Technology Labs Inc.
Office: +1-321-254-8118
Mobile: +1-321-795-6201
1430 Sarno Rd.
Melbourne, FL 32935
USA
Email: jrbr...@asttechlabs.com
Website: www.asttechlabs.com
///////////////////////////////////////////////////
-----Original Message-----
From: sip-implementors-boun...@lists.cs.columbia.edu
<sip-implementors-boun...@lists.cs.columbia.edu> On Behalf Of wodb0...@daum.net
Sent: Thursday, December 17, 2020 9:31 AM
To: sip-implementors@lists.cs.columbia.edu
Subject: Re: [Sip-implementors] [SIPForum-discussion] RTP Volume Values
-----Original Message-----
From: Zuñiga, Guillermo <guillermo.zun...@cwpanama.com>
Sent: Tue, 6 Jun 2017 20:52:04 +0000
To: "SIP FORUM" <discuss...@sipforum.org>,<br>
"sip-implementors@lists.cs.columbia.edu"
<sip-implementors@lists.cs.columbia.edu>
Subject: [SIPForum-discussion] RTP Volume Values
Hi fellows,
I would like you can help me with the following issue.
I am sending a DTMF event packet to a carrier and the carrier is just decoding
the DTMF for the first RTP and when I send the second RTP values doesn´t.
I am not clear with the Volume values, I was trying looking for information
about this values and how is measured.
This value could be affecting that carrier is not recognizing the dtmf?
Where I can find information about this value?
DTFM for call completed:
Real-Time Transport Protocol
[Stream setup by SDP (frame 234844)]
[Setup frame: 234844]
[Setup Method: SDP]
10.. .... = Version: RFC 1889 Version (2)
..0. .... = Padding: False
...0 .... = Extension: False
.... 0000 = Contributing source identifiers count: 0
0... .... = Marker: False
Payload type: telephone-event (96)
Sequence number: 307
[Extended sequence number: 65843]
Timestamp: 45440
Synchronization Source identifier: 0x6c97d60e (1821890062) RFC 2833 RTP
Event
Event ID: DTMF One 1 (1)
0... .... = End of Event: False
.0.. .... = Reserved: False
..00 0110 = Volume: 6
Event Duration: 1200
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
DTMF for call Not completed:
Real-Time Transport Protocol
[Stream setup by SDP (frame 133217)]
[Setup frame: 133217]
[Setup Method: SDP]
10.. .... = Version: RFC 1889 Version (2)
..0. .... = Padding: False
...0 .... = Extension: False
.... 0000 = Contributing source identifiers count: 0
0... .... = Marker: False
Payload type: telephone-event (96)
Sequence number: 811
[Extended sequence number: 66347]
Timestamp: 124240
Synchronization Source identifier: 0xbaca1533 (3133805875) RFC 2833 RTP
Event
Event ID: DTMF One 1 (1)
0... .... = End of Event: False
.0.. .... = Reserved: False
..00 1101 = Volume: 13
Event Duration: 960
+++++++++++++++++++++++
Regards
Guillermo
Thanks a lot for all your help.
Guillermo Zuniga
Especialista de Soporte Técnico
Gerencia de Soporte Técnico
Tel: +507 263-6671
Cel: +507 6670-0481
Fax: +507 265-3295
Email: guillermo.zun...@cwpanama.com
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