[Asterisk-Users] VAD/DTX implementation through zaptel cards

[Steve Kann]

On Apr 16, 2005, at 4:32 AM, parijat wrote:

>
> Hi,
> Thanks for helping me out.
>
> I want to clear out few more points
>
> 1) zaptel cards receive PCM from PSTN.

They receive it in either uLaw, aLaw, or signed linear PCM, depending 
on the model and what it's connected to.

> In what form do they give it to
> asterisk.
>  Do Zaptel cards CODE/DECODE PCM from PSTN to RTP or zaptel cards
> forward PCM to asterisk which converts it to RTP.

They give it to the drivers in whatever form they have.  The drivers 
may convert it amongst those formats.

Asterisk doesn't always use RTP.

>
> 2) If asterisk does that conversion then, using which file
> does it convert. I want to change code of that file so that I can 
> implement
> VAD.

Did you do even the most basic research here before asking this 
question?

If you can't find the codec files, you obviously didn't even look.


> 3) If all this is not possible then why they have give so many codec 
> files
> in asterisk.
>

All _what_ is not possible?  Anything is possible.  It would be 
possible to implement VAD and DTX for zaptel cards in software.

-SteveK


> Regards,
> Parijat
>
> -----Original Message-----
> From: asterisk-users-bounces at lists.digium.com
> [mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Steve
> Underwood
> Sent: Tuesday, April 12, 2005 9:40 PM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: Re: [Asterisk-Users] VAD/DTX implementation through zaptel 
> cards
>
> Steve Kann wrote:
>
>> Eric Wieling wrote:
>>
>>> parijat at varaha.com wrote:
>>>
>>>> Hi,
>>>> How can i implement VAD/DTX using zaptel with asterisk towards PSTN.
>>>
>>>
>>>
>>> TDM (PSTN/telcos) do not support VAD. The entire idea of VAD is not
>>> even a valid idea.
>>
>>
>> Doing VAD on audio coming _from_ the TDM world certainly is something
>> you might want to do, to dramatically reduce the bandwidth you consume
>> when sending the audio via VoIP channels.
>>
>> This kind of thing is not presently implemented in *, though, but it
>> could be. (note: doing it well will require a bunch of CPU, though. I
>> wonder if it could be done in the same DSP that is doing
>> echo-cancellation on the new TE4xxP boards?
>
> Unless Digium's plans changed since the last time I spoke to Mark, the
> answer would be no. I believe they are using a dedicated function echo
> canceller device.
>
> Regards,
> Steve
>
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