[Asterisk-Users] An anniversary and a lament for FXOs

[Peter Svensson]

On Fri, 5 Nov 2004, Ryan Thrash wrote:

> What about an expensive Supermicro dual Xeon PCI-X system with 1GB ECC 
> RAM and a hardware RAID controller (it was SATA, though)?
> 
> Echo was noticeable even on SIP-to-SIP calls internally with the 
> system, with all sorts fo tweaks to tx/rx gain. Supermicro, too. Oh 
> yeah, and we were on a T1 PRI, which is not *supposed* to have echo. 
> Unfortunately when I left the company, they finally replaced the phone 
> system to get rid of the echo and customer complaints.

The sip<->sip echo sounds really strange. What was the audio path? 
   phone<-sip->asterisk<-sip->phone 
or 
   phone<-sip->phone
or some other path?

A T1 connection just means that that particualr call leg does not 
introducce echo. The most common point to introduce echo is at a two wire 
last leg. A digital path is in effect a four wire leg - i.e. the receive 
and transmit paths are separate and can not leak into one another. If you 
are on a T1+sip all digital connection the *you* can still hear echos 
caused by your customers.

If your customers still hear echos even though your path is fully digital 
the you may have an echo canceler somewhere in the path that actaully adds 
the echo. This can happen if the path characteristics change or if the 
echo canceler converges to an incorrect solution.

Peter