| Author |
|
grcgrc
Intermediate
Joined: August 16 2006
Posts: 6
|
| Posted: August 16 2006 at 10:46am | IP Logged
|
|
|
Does version 5.12 support out of band DTMF signalling as per RFC 2833? This is crucial to support IVR applications with the low bandwidth codecs like G.729 and G.723.1. If not, is it planned for v5.13?
Regards,
Guillermo
|
| Back to Top |
|
| |
support
Administrator
Joined: January 26 2005
Location: United States
Posts: 1666
|
| Posted: August 16 2006 at 12:42pm | IP Logged
|
|
|
Hi Guillermo,
Thanks for posting your questions to the support forum.
v5.12 of the VOIP Media Engine does not yet support out of band DTMF as per RFC2833.
You have hit the nail right on the head - we need this capability as soon as possible. I know it will be available in the v5.13 release. Our software developers are busy implementing this (and other) new functionality as we speak.
We do not yet have a firm release date for v5.13. We anticipate it to be available soon however.
Repost as needed,
Support
|
| Back to Top |
|
| |
grcgrc
Intermediate
Joined: August 16 2006
Posts: 6
|
| Posted: August 16 2006 at 1:13pm | IP Logged
|
|
|
Thanks for the quick reply.
What experience have you had with the low bit codecs and DTMF detection? Is iLBC any better than G.729 for this?
|
| Back to Top |
|
| |
support
Administrator
Joined: January 26 2005
Location: United States
Posts: 1666
|
| Posted: August 16 2006 at 2:49pm | IP Logged
|
|
|
Hi Guillermo,
We do have customers using the media engine to decode DTMF from the iLBC and G729 media streams of a VOIP call. They say it works for what they want to do. That’s their choice. Part of the reason they report success lies in how we implemented the internal DTMF decoder block. Even with “lossy” codecs such as G729 and iLBC, the distortions in the channel do not completely overcome the ability to pick out distorted DTMF tones. The smarter the DTMF decoder, the less false positive detections occur – up to a point.
Let me explain further:
Both G729 and iLBC are sampled at 8kHz. Due to the laws of sampling theory, the max frequency that can be used in the voice channel with these codecs is 4kHz. This is ˝ the sampling rate.
A 4kHz voice channel is enough bandwidth to send DTMF in-band signaling. The table below shows the standard DTMF frequencies:
The reason why (in theory) in-band DTMF cannot be used with G729 and iLBC is because these codecs are “lossy”. What this means is that these codecs introduce distortion in the in-band signal channel which makes DTMF decoding unreliable.
In-band DTMF signaling can only theoretically be 100% accurate if the signal channel does not introduce added distortions – such as the case with using 8kHz uLaw or aLaw codecs.
If you chose to use in-band DTMF with G729 or iLBC – which codec is better? We like iLBC.
As a test:
The trial VOIP Media Engine comes with sample applications. Fire up the 2 line IVR app and the single line soft phone. Call the IVR server using either iLBC or G729. The IVR server will be able to decode received DTMF from your soft phone.
Hope this helps.
Support
|
| Back to Top |
|
| |
grcgrc
Intermediate
Joined: August 16 2006
Posts: 6
|
| Posted: August 23 2006 at 8:10pm | IP Logged
|
|
|
I really want to congratulate you on a clear, concise and accurate answer!
I hope 5.13 is just around the corner. My application s pure IVR and relies on accurate DTMF detection.
Thanks again,
Guillermo
|
| Back to Top |
|
| |
support
Administrator
Joined: January 26 2005
Location: United States
Posts: 1666
|
| Posted: August 24 2006 at 8:11am | IP Logged
|
|
|
Hi Guillermo,
Thanks for your kind words.
v5.13 is coming soon and it will definitely support the out of band DTMF capability we previously talked about.
Other possible option to speed things up:
If you cannot wait until we officially release v5.13, we can perform custom work on the product right now on a contract basis (hourly rate or fixed).
Support
|
| Back to Top |
|
| |
Active Topics 
Member List 
Search 
Help 
Register 
Login
LanScape Support Forum -> LanScape VOIP Media Engine™ - Pre-Sales Technical Support
Topic: DTMF Detection
