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

[Robinson Tim-W10277]

Michael

The problem lies not with Asterisk or the cards but with the combination
of voip and analogue telephony in general.  I can guarantee that you
will have very similar echo when you connect your Panasonic pbx to the
analogue lines.  In fact, your echo will most likely be worse. It is
just that you do not perceive it as echo because it occurs more or less
coincident with the original sound.

However, the propagation delay through the systems that is introduced by
Asterisk and voip (by necessity and design) is the culprit, because this
adds the delay which causes the echo to become perceptable.

You will never get a match good enough to eliminate echo.  What you may
be able to do is to get a match that is good enough to allow the
built-in echo cancellers to be effective.

You don't say where you hear the echo - near end or far end?  A small
diagram of your system posted on your web site, with an indication of
who hears the echo and which echo they are hearing would help me (or
countless others!) to help you work this out.

I am using 2 X100P cards here in the UK connected to extension ports of
a Panasonic KXT616 and we get no perceptable echo at all.

Good luck!

Rgds
Tim Robinson

-----Original Message-----
From: asterisk-users-bounces at lists.digium.com
[mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of
mgraves at mstvp.com
Sent: 03 November 2004 15:14
To: Asterisk Group
Subject: [Asterisk-Users] An anniversary and a lament for FXOs


This week marks one year since I first setup an Asterisk server in the
hopes of transitioning my home office to a total VoIP system. The
process has been an incredible learning experience. I've tried numerous
IP hard phones, eventually settling upon the Polycom IP600 as my choice.
I've also used multiple ATAs including all the Sipura products. Using
Asterisk has been a challenge, a thrill and (when its working) a joy.
However, the one thing that I am not satisfied with is the performance
of the FXO interfaces that bring in my PSTN lines.

I've tried X100p cards but found them horribly unreliable. I presently
use Sipura SPA-3000s but they're only marginally better. How is it that
my Panasonic 4 line SOHO phone system (KX-TG4000B) can have four stable,
reliable FXOs with no echo at all in a device with a total cost of
<$500? It seems to me that there ought to be hardware available that
behaves just as well, but bridges the PSTN to the SIP/IAX domain?

I've read a lot on the list about how difficult designing FXOs can be,
but that flies in the face of the fact that every small multi-line phone
system has them...and without expection those behave better than the
devices I've been able to try with Asterisk. The Sipura SPA-3000 has
several settings to adjust for line impedance and inductive/capacitive
line loading....lots of settings, but it provides nowhere near the basic
performance of one of the lines on the Panasonic KSU. It's simply mind
boggling.

So, while I've posted with respect to FXOs previously, I must ask
again....what FXO interface device can anyone recommend from real
experience?

Michael

P.S.  -  I even investigated switching my lines to ISDN to get around
the need for FXOs, but SBC won't do it where I live.
--
Michael Graves                           mgraves at pixelpower.com
Sr. Product Specialist                          www.pixelpower.com
Pixel Power Inc.                                 mgraves at mstvp.com

o713-861-4005
o800-905-6412
c713-201-1262




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