[Asterisk-biz] T1 Technology and VoIP Gateway Primer

[Matt Roth]

Alex,

Thank you for your answers to the questions at the bottom of my post.

>You are somewhat confused...You are severely confused...
>
No doubt about it, I'm a bit of a newb and am working on developing a 
larger scale Asterisk system than I see commonly documented.  This stuff 
is a first pass and I appreciate any corrections to it.  Better now than 
later, believe me!  ; )

>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"?

>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?

>They are not subtle and they are very clear.
>  
>
>There's no difference. DS1 is a standard signaling with 1.54Mbps raw
>capacity. T1 is a product name for DS1 by your carriers. PRI is "primary
>rate ISDN" which is DS1 partitioned into 23 "Bearer" channels for calls,
>and one "Data"  channel for ISUP call signaling.
>  
>
I should have prefixed that statement with, "To my knowledge."  Thank 
you for the clear explanation.

Matthew Roth
http://voip-info.org/tiki-index.php?page=Running%20Asterisk%20on%20Debian