[Asterisk-Users] VAD, CNG, for Zap

[yusuf]

Hi,

I have a few questions that I have been researching for a while. Sorry 
if it is a bit long winded?
I have a huge need for VAD and CNG support in Asterisk, as my bandwith 
is *very * limited and expensive, and VAD, CNG and DTX will save me 
alot, at least 30 - 50%.  I have installed and am using the 
SVN-bweschke-bug_5374-r9733, which adds VAD and silence suppression 
support to Asterisk.  However, my understanding(and i am hoping people 
will correct me) is that VAD and CNG is based on the codec being used, 
so if g723 is being used, it will detect silence, and the codec will set 
a silence tag, which will tell asterisk this is silence, so generate 
comfort noise.  So all of this will work if both endpoints of a 
particular call is using SIP with g723(for example).  However,if one or 
both of the voice endpoints are ZAP, will CNG and VAD still be possible.?

My topology is an Asterisk with an E1, calls come into the E1 from a 
PBX, and then get trunked to another Asterisk box, then go out on that 
E1.  And since ZAP is analogue, is it possible for it to support silence 
suppresion and VAD?

So, my question again, is silence suppresion possible when ZAP is involved

I would greatly appreciate any pointers/suggestions.
thanks,
yusuf