[Freeswitch-users] VAD and CN question

[Michael Jerris]

A big thanks to Tamas and Steve Underwood for putting this new page  
together:

http://wiki.freeswitch.org/wiki/VAD_and_CNG

Mike

On Sep 15, 2008, at 5:14 AM, Sluschny, Thomas wrote:

> thank you very much Tamas,
> i found this infos very useful :)
>
> -----Ursprüngliche Nachricht-----
> Von: freeswitch-users-bounces at lists.freeswitch.org [mailto:freeswitch-users-bounces at lists.freeswitch.org 
> ] Im Auftrag von Tamas
> Gesendet: Samstag, 13. September 2008 14:31
> An: freeswitch-users at lists.freeswitch.org
> Betreff: Re: [Freeswitch-users] VAD and CN question
>
>
> 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
>>
>
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