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

[parijat]

Hi,
Thanks for helping me out.

I want to clear out few more points

1) zaptel cards receive PCM from PSTN. 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.

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.  

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

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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