[Asterisk-biz] T1 Technology and VoIP Gateway Primer

[alex at pilosoft.com]

On Thu, 28 Apr 2005, Matt Roth wrote:

> >I do not understand what distinction you are trying to make between "PSTN" 
> >and "CPE". 
> >
> The distinction I'm trying to make is between our hardware and the
> carrier's.  To be clear, the CPE side will be the equipment we will be
> responsible for purchasing, configuring, and maintaining.  The PSTN side
> will be the T-1 that we order and have configured for us from the
> carrier (up to the demarcation point).  I looked at what was happening
> on the PSTN side primarily in order to better understand the signal we'd
> be receiving and how it is processed.  Hopefully, this will lead to
> predicting and circumventing hardware bottlenecks before they happen.  
> Do you or anyone else have any suggestions for terms other than "PSTN"  
> and "CPE"?
Does it really matter? Network is symmetric. Your "PSTN" is "CPE" to 
carrier. So you should probably refer to those as "FXO" and "FXS".

> >http://home.comcast.net/~mroth01/T1-PSTN.gif
> >Generally, you don't refer to the ulaw codec as DSP.
> >
> Thanks for pointing that out.  I erroneously believed that the
> companding occurred after the analog-to-digital conversion, on the
> digital signal.  After checking here
> (http://en.wikipedia.org/wiki/Companding) I see that the compressing
> occurs before ADC and the expanding occurs after the DAC, both on the
> analog signal.  Since my setup will be strictly digital (no analog
> phones on our side), I do not have to worry about this. Other people
> may, so for their benefit, could you explain where the µ-law codec fits
> into the equation, and if it is resource-intensive if it needs to be
> performed on the Asterisk server?  Also, should I relabel the codec as
> "G.711 µ-law" in my diagram?
u-law is just your basic ADC/DAC. Your input is analog signal and your 
output is g.711 u-law stream. 

-alex