[Freeswitch-users] VAD and CN question

[Tamas]

Hello,

to answer for my own email - for other who might be interested...


Tamas írta:
> Hello,
>
> I've talked about CNG, VAD with Anthony and Brian already but I still
> have a mess in it and don't really know how it works.
>
> Could anybody explain the practical side of these magic options?
>
> 1. What does suppress_cng=true do exactly? (yep, I know it suppresses
> CNG, but what does this mean? Won't send out the CN/8000 rtpmap in SDP?)
>   
suppress-cng and suppress_cng are used to manage the sending of CN RTP
packets after agreement through SDP.

> 2. What do VAD settings do in sofia profile? I've read
> http://wiki.freeswitch.org/wiki/Sofia.conf.xml
>
>    <!-- <param name="vad" value="in"/> -->
>    <!-- <param name="vad" value="out"/> -->
>    <!-- <param name="vad" value="both"/> -->
>
> What do these options do in practice? Can FS detect silence (e.g. no
> RTP?) and than what can it do with?
>   
When VAD is turnd on, FS checks on the given channel for incoming or/and
outgoing channel (depends on the settings) and when detects silence,
stops sending out RTP.

> 3. I found undocumented options rtp_enable_vad_in, rtp_enable_vad_out
> for sofia which might be the per call settings for point 2. ? If this is
> correct, what will this do?
>             <action application="set" data="rtp_enable_vad_in=true"/>
>             <action application="set" data="rtp_enable_vad_out=true"/>
>            <action application="bridge" data="sofia/....."/>
>   
These settings are the same as in 1. but can be used per call.

> 4. What will FS do when one side of the bridge supports CN but the other
> doesn't?
> E.g. softphone->FS->GW (sends CN packets)
> the softphone does not support CN
> Would it be possible to turn on comfort noise generation in FS for the
> side which cannot handle CN?
>   
When on side does not support CN, FS simply won't forward CN RTP
packets. Comfort noise generation into media channel in FS is possible with
bridge_generate_comfort_noise=true
added in r9543. More about on http://wiki.freeswitch.org/wiki/VAD_and_CNG

> 5. Is it possible to let FS detect silence and on one leg send CN
> packets insted of RTP?
> E.g. softphone->FS->GW (sends  CN packets)
> the softphone does not support CN, but for saving bandwidth it would be
> good to have silence detection and in case of silence FS lets send CN
> instead of RTP.
>   
Yes, possible. VAD has to be turned on that channel and both sides have
to agree on CN RTP packets (in SDP).

> Sorry for my dump questions, I would like to understand the whole picture.
>   
I hope I'm on the right way :)

> I would like to add the clarification to FS wiki to lets other have less
> troubles (with endpoints on one side supporting VAD/CNG and endpoints on
> other side not supporting VAD/CNG, e.g. CallWeaver)
>   
Check
http://wiki.freeswitch.org/wiki/VAD_and_CNG
> Thanks in advance!
>
> Regards,
>     Tamas
>   

Tamas