asterisk users - Oct 2003 - X100P Echo Problems..What's going to happen?

I've read and experienced the echo problems with the X100P.  Is Digium
going to fix the problem or refund our money?  I want to see this work
because myself and other small companies out there use analog lines.  I
would trade up to T1 but that requires me to have at least 9 lines.  If
I did trade up, do the T1 cards work perfectly with no echo at all?  I
get echo with my directly connected computer using Xten SIP.  No matter
with all the suggestions to change the parameters, it still has echo.
 
Does anyone have the T1 and have no problems at all?  I would surely
appreciate you experiences.  What's my option to get this too work
flawlessly?
 
John
 
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> I've read and experienced the echo problems with the X100P.  Is Digium
> going to fix the problem or refund our money?  I want to see this work
> because myself and other small companies out there use analog lines.  I
> would trade up to T1 but that requires me to have at least 9 lines.  If
> I did trade up, do the T1 cards work perfectly with no echo at all?  I
> get echo with my directly connected computer using Xten SIP.  No matter
> with all the suggestions to change the parameters, it still has echo.
Can you explain what you have tried?  If it's _you_ who is getting the echo 
(not the party calling you) and you just can't kill it, the culprit often 
enough seems to be your PSTN interface; near-end echo is largely caused by 
impedance mismatches in the hybrid circuit (the circuit which converts the 
4-line interface to the 2-line one) -- the software echo cancellers just 
try and get rid of the echo in software but the problem is often a hardware 
issue.

Just to reiterate the possible solutions that I am aware of:
- try different echo cancel algorithms (mark2 with agressive mode is what I 
use)
- reduce or increase the number of taps (echocancel=yes is equivalent to 
echocancel=128) -- the fewer taps the better, but more taps may be 
necessary to eliminate echo.
- try reversing the ring and tip on the FXO interface
- try attaching the FXO card right at the demarcation point and remove ANY 
other equipment connected at the point of demarcation.  Stubs can play 
havoc with echo cancellation
> Does anyone have the T1 and have no problems at all?  I would surely
> appreciate you experiences.  What's my option to get this too work
> flawlessly?
I am currently experimenting with the T1 card and a channel bank to see if 
"telco-grade" equipment will do a better job of removing echo. 
I'm waiting
on a cable before I can start testing though.  :-( 

I have a Carrier Access Channel Bank I with 12 FXO ports on it, and an Adit 
600 with 12 FXS ports coming soon.  the CBI is pretty old and I've heard 
that it cannot do far-end disconnect detection but the FXO cards claim that 
they dynamically adjust to compensate for impedance changes to minimize 
echo, so I'm keen on seeing what they can do.

I just got pricing from our telco (Bell Canada) and to purchase an entire 
ISDN PRI (23B+D) with 30DID and 911 service, the per-line cost is almost 
identical to regular analogue PSTN ports.  There'd be no echo on those 
babies, I imagine, since there's no hybrid circuit until you hit the other 
end of the call.

Regards,
Andrew

John:
I have been around voice over data packets for quite a few years and I am
still to see the perfect system that works identical to circuit switching
100% of the time.  My opinion is that there is a lot more to the story than
just parameters.  Packet loses, double compressions, faulty routers,
bandwidth, analog to digital and so on can get in the way.
On the other hand, if your customer understand the benefits, and I mean more
than cost, and can leave with 80% perfect, then you will be able to
understand why a lot of companies have opted for VoIP (or ATM or Frame
Relay).
Regards,
Uriel
 -----Original Message-----
From: asterisk-users-admin@lists.digium.com
[mailto:asterisk-users-admin@lists.digium.com]On Behalf Of John M
Sent: Monday, October 13, 2003 1:41 AM
To: asterisk-users@lists.digium.com
Subject: [Asterisk-Users] X100P Echo Problems..What's going to happen?
Importance: High


  I've read and experienced the echo problems with the X100P.  Is Digium
going to fix the problem or refund our money?  I want to see this work
because myself and other small companies out there use analog lines.  I
would trade up to T1 but that requires me to have at least 9 lines.  If I
did trade up, do the T1 cards work perfectly with no echo at all?  I get
echo with my directly connected computer using Xten SIP.  No matter with all
the suggestions to change the parameters, it still has echo.



  Does anyone have the T1 and have no problems at all?  I would surely
appreciate you experiences.  What's my option to get this too work
flawlessly?



  John



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On Tuesday, October 14, 2003 8:32 AM, Eric Wieling 
[SMTP:eric@fnords.org] wrote:
> Where does the 4 wire change to a 2 wire?
>
4 to 2 wires happen anywhere the signal goes from digital to a cable 
pair. First the digital signal is converted to an analog 2 wire for 
transmit and from 2 wire analog to digital for receive. On the analog 
side the signals are combined from 2 pair to 1 pair. Examples would be 
a channel unit in a channel bank or line equipment in a telephone 
switch. It can also happen in an 4 wire analog to a 2 wire analog as 
can be used to conserve cable pair but this is not as common.

Don Pobanz
> On Tue, 2003-10-14 at 03:30, Mark Spencer wrote:
> > Echo has nothing to do with TCP vs. UDP.  It's an analog
phenomenon
> > that
> > occurs where the "hybrid" is, where the four-wire circuit
changes
to
> > a
> > two-wire circuit.
>
> --
> Sample configs and more: http://www.fnords.org/~eric/asterisk/
>
> BTEL Consulting
> +1-850-484-4535 x2111 (Pensacola)
> +1-504-595-3916 x2111 (New Orleans)
> +1-877-677-9643 x2111 (Toll Free)

>Where does the 4 wire change to a 2 wire?
with just a x100p that would be at the telco in their switching gear
where they do the a/d to route the call
but if you have a channel bank withn T1 to * then you have the a/d at the
telco switch
and then again more a/d when coming off channel banks fxo to  T1 inerface in
*

you can also get echo because of a an impedance mismatch between the analog
line trunk
from the telco and the x100p (eg tip/ring reversed, incorrectly provisioning
on the analog line)

so much for theory ..:)
Now i have  questions
1)  how do you actually measure the impedance that is provisioned on the
line ??
2) what impedance does the x100 expect ??