Codec support for Cisco VXML Gateway

[Vamsi Daggubati]

Hi,

I am new to UniMRCP. We are using UniMRCP with Cisco with GSR, GSS and GDF Plugins. I have successfully installed and configured my UniMRCP setup. While testing, I ran into an audio codec issue. 

My company's Cisco VXML gateway only supports audio file codec of type "Mu-Law mono 8000Hz 64kbps". 

We just verified the unimrcpserver.xml file and found that current setting is below one which our gateway doesn't support.

 

<codecs own-preference="false">PCMU PCMA L16/96/8000 telephone-event/101/8000</codecs>

What is the codec setting that supports the Cisco VXML gateway?

Any help would be appreciated!

Thanks,

Vamsi Daggubati

[Mohan Karki]

What error are you seeing?

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[Vamsi Daggubati]

There is no error from MRCP side. MRCP is successfully able to establish RTP conection to VXML gateway and streaming. But gateway was not able to play the audio and throwing "error.badfetch". My best guess is the unsupported Codec.

Default setting is PCMA-Law

But our gateway only supports MU-Law with 8000Hz and 64kbps bit rate

What is the codec setting for ths in unimrcpserver.xml?

[Mohan Karki]

If you can post the unimrcp logs, i can help. i recently did this.

[Vamsi Daggubati]

Attached are the UniMRCP logs and UniMRCP server config.

Thanks

[Vamsi Daggubati]

BTW, I forgot to mention. 10.3.74.80 is IP for UniMRCP and 10.3.74.99 is IP for VXML Gateway.

Regards,

Vamsi Daggubati

[Mohan Karki]

I use MRCPV2, set the following vxml property and corresponding voice class defined in gateway. 

PCMU should work for you.

  <property name="com.cisco.tts-server" value="sip:t...@10.190.66.1xx:5060" />

[Vamsi Daggubati]

Thanks for the reply.

We are using mrcpv2 as well. We have already set this configuration in VXML gateway as per Cisco's guide. 

Additionally, I changed umsgss.xml config to save waveforms. I verified those waveforms in Audacity/Goldwave and found that their codec is PCMA 8000Hz 128 KBPS. 

Also, when I dial in to this application, I hear some static noise instead of TTS. This seems to be the case of unsupported codec.

[Arsen Chaloyan]

Hi Vamsi,

> My company's Cisco VXML gateway only supports audio file codec of type "Mu-Law mono 8000Hz 64kbps". 

The corresponding RTP codec is outlined below

<codecs own-preference="false">PCMU PCMA L16/96/8000 telephone-event/101/8000</codecs>

and defined here

https://tools.ietf.org/html/rfc3551#section-4.5.14

This is very clear and out of question.

Also, following the logs that you provided, I can tell that PCMU was used in the communication between CVP and UniMRCP server. In fact, there were two SIP/MRCPv2 sessions established: one for speech synthesis and the other for speech recognition. The latter was not even used.

Here are some logs regarding RTP streams.

2018-09-11 16:22:31:999207 [INFO]   Open RTP Transmitter 10.3.74.80:5000 -> 10.3.74.99:16684

2018-09-11 16:22:31:999214 [INFO]   Media Path 0x7f00c4001a58 Source->[LPCM/8000/1]->Bridge->[LPCM/8000/1]->Encoder->[PCMU/8000/1]->Sink

2018-09-11 16:22:32:019189 [INFO]   Open RTP Receiver 10.3.74.80:5002 <- 10.3.74.99:16764 playout [50 ms] bounds [0 - 600 ms] adaptive [1] skew detection [1]
2018-09-11 16:22:32:019197 [INFO]   Media Path 0x7f00c4003d78 Source->[PCMU/8000/1]->Decoder->[LPCM/8000/1]->Bridge->[LPCM/8000/1]->Sink

2018-09-11 16:22:34:379159 [INFO]   Close RTP Receiver 10.3.74.80:5002 <- 10.3.74.99:16764 [r:0 l:0 j:0 p:50 d:0 i:0]

2018-09-11 16:22:34:379329 [INFO]   Close RTP Transmitter 10.3.74.80:5000 -> 10.3.74.99:16684 [s:91 o:14560]

You can see that no RTP packets were received, which is expected, as no RECOGNIZE was reached the server. In the meantime, the server sent 91 RTP packets, which I strongly believe contained the intended audio data.

BTW, you can make a network capture and not only follow the RTP stream but also listen to the synthesize audio.

> Additionally, I changed umsgss.xml config to save waveforms. I verified those waveforms in Audacity/Goldwave and found that their codec is PCMA 8000Hz 128 KBPS. 

This would be very hard for me to believe. The stored wave file must be in clear PCM. If you send the file, I'll double check.

> Also, when I dial in to this application, I hear some static noise instead of TTS. This seems to be the case of unsupported codec.

Post your VoiceXML file to check what might be wrong. There must be something specific to your environment.

--

Arsen Chaloyan
Author of UniMRCP
http://www.unimrcp.org

[Vamsi Daggubati]

Thanks Arsen,

I have removed the PCMA part from the <codec> tag and TTS now works!!

Here is the final codec tag config that worked for me...

<codecs>PCMU telephone-event/101/8000</codecs>

Thanks for your Help!!