asterisk users - Oct 2004 - Chaining more than one zap echo canceller?

I have Asterisk connected to a channel bank via a t100p card. There
excessive sidetone generated on the analog side due to an impedance mismatch
- I am very close to my serving CO which brings the line down to about
150ohms and the channel bank is expecting 600ohms. However, the very loud
sidetone is being fairly effectively supressed by the zap echo canceller and
I have quite usable lines as a result.

 From time to time calls are placed to other PSTN numbers (even terminating
off of the same CO) that are introducing their own far end echo component on
the line and it isn't being supressed at all - thus my outbound callers
begin to hear their own voice and get very frustrated. I have to assume the
second reflection couldn't be supressed by design - the zap echo can has
already locked on to the sidetone echo after all.

 So, I have a fix for the sidetone/impedance problem (PRI on order) however
is it possible to insert another can into the system somehow? For example,
if I were to run TDMoE to a second box and access to the t100p/channel bank
through there?

Any suggestions welcome (apart from curing the sidetone)  :-)

Kris Boutilier
Information Systems Coordinator
Sunshine Coast Regional District

> I have Asterisk connected to a channel bank via a t100p card. There
> excessive sidetone generated on the analog side due to an impedance
mismatch
> - I am very close to my serving CO which brings the line down to about
> 150ohms and the channel bank is expecting 600ohms.
where/how did you measure this ?
> However, the very loud
> sidetone is being fairly effectively supressed by the zap echo canceller
and
> I have quite usable lines as a result.
>
>  From time to time calls are placed to other PSTN numbers (even
terminating
> off of the same CO) that are introducing their own far end echo component
on
> the line and it isn't being supressed at all - thus my outbound callers
> begin to hear their own voice and get very frustrated. I have to assume
the
> second reflection couldn't be supressed by design - the zap echo can
has
> already locked on to the sidetone echo after all.
>
>  So, I have a fix for the sidetone/impedance problem (PRI on order)
however
heh looks like your in BC, is replacing with  a pri cost effective in my
calc's
here the break pt is usually about 16-18 analog lines ?
> is it possible to insert another can into the system somehow?
some of us that have been around the block a few times with this fscking
echo echo echo
have ended up buying an inline hardware echo can between the T1xx/T4xx
and the channel bank then turn off all echo cans in asterisk
i have used the Tellab 2572 64ms and have crystal clear sound others report
the same
google for some other brands other have used ...
(its prolly more cost effective that buying the PRI here in BC as well :)

If you're certain it is an impedance problem and the impedance of your 
line is lower than that of the CO, you can increase the impedance of 
your line by putting a potentiometer in-line and adjusting it until the 
sidetone disappears.  This is a bare-bones solution and decreases the 
efficiency of the line because you're putting in pure resistance.

If your impedance is higher than the CO, or if you want to be more 
efficient, you'll need a more complicated impedance matching network.

On Oct 12, 2004, at 10:26 AM, Kris Boutilier wrote:
>  I have Asterisk connected to a channel bank via a t100p card. There
> excessive sidetone generated on the analog side due to an impedance 
> mismatch
> - I am very close to my serving CO which brings the line down to about
> 150ohms and the channel bank is expecting 600ohms. However, the very 
> loud
> sidetone is being fairly effectively supressed by the zap echo 
> canceller and
> I have quite usable lines as a result.
>
>  From time to time calls are placed to other PSTN numbers (even 
> terminating
> off of the same CO) that are introducing their own far end echo 
> component on
> the line and it isn't being supressed at all - thus my outbound callers
> begin to hear their own voice and get very frustrated. I have to 
> assume the
> second reflection couldn't be supressed by design - the zap echo can 
> has
> already locked on to the sidetone echo after all.
>
>  So, I have a fix for the sidetone/impedance problem (PRI on order) 
> however
> is it possible to insert another can into the system somehow? For 
> example,
> if I were to run TDMoE to a second box and access to the t100p/channel 
> bank
> through there?
>
> Any suggestions welcome (apart from curing the sidetone)  :-)
>
> Kris Boutilier
> Information Systems Coordinator
> Sunshine Coast Regional District
>
> _______________________________________________
> Asterisk-Users mailing list
> Asterisk-Users@lists.digium.com
> http://lists.digium.com/mailman/listinfo/asterisk-users
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>    http://lists.digium.com/mailman/listinfo/asterisk-users

True, but you can make an apple pie taste better by adding a little
orange juice....

Jim Shilliday


-----Original Message-----
From: Rich Adamson [mailto:radamson@routers.com] 
Sent: Tuesday, October 12, 2004 3:58 PM
To: Asterisk Users Mailing List - Non-Commercial Discussion
Subject: Re: [Asterisk-Users] Chaining more than one zap echo canceller?

Impedance does not equal resistance. Apples and oranges.

------------------------
> If you're certain it is an impedance problem and the impedance of your
> line is lower than that of the CO, you can increase the impedance of 
> your line by putting a potentiometer in-line and adjusting it until
the 
> sidetone disappears.  This is a bare-bones solution and decreases the 
> efficiency of the line because you're putting in pure resistance.
> 
> If your impedance is higher than the CO, or if you want to be more 
> efficient, you'll need a more complicated impedance matching network.
> 
> On Oct 12, 2004, at 10:26 AM, Kris Boutilier wrote:
> 
> >  I have Asterisk connected to a channel bank via a t100p card. There
> > excessive sidetone generated on the analog side due to an impedance 
> > mismatch
> > - I am very close to my serving CO which brings the line down to
about
> > 150ohms and the channel bank is expecting 600ohms. However, the very
> > loud
> > sidetone is being fairly effectively supressed by the zap echo 
> > canceller and
> > I have quite usable lines as a result.
> >
> >  From time to time calls are placed to other PSTN numbers (even 
> > terminating
> > off of the same CO) that are introducing their own far end echo 
> > component on
> > the line and it isn't being supressed at all - thus my outbound
callers
> > begin to hear thei          rownvoiceandgetveryfrustrated.Ihaveto
> > assume the
> > second reflection couldn't be supressed by design - the zap echo
can
> > has
> > already locked on to the sidetone echo after all.
> >
> >  So, I have a fix for the sidetone/impedance problem (PRI on order) 
> > however
> > is it possible to insert another can into the system somehow? For 
> > example,
> > if I were to run TDMoE to a second box and access to the
t100p/channel 
> > bank
> > through there?
> >
> > Any suggestions welcome (apart from curing the sidetone)  :-)
> >
> > Kris Boutilier
> > Information Systems Coordinator
> > Sunshine Coast Regional District
> >
> > _______________________________________________
> > Asterisk-Users mailing list
> > Asterisk-Users@lists.digium.com
> > http://lists.digium.com/mailman/listinfo/asterisk-users
> > To UNSUBSCRIBE or update options visit:
> >    http://lists.digium.com/mailman/listinfo/asterisk-users
> 
> _______________________________________________
> Asterisk-Users mailing list
> Asterisk-Users@lists.digium.com
> http://lists.digium.com/mailman/listinfo/asterisk-users
> To UNSUBSCRIBE or update options visit:
>    http://lists.digium.com/mailman/listinfo/asterisk-users
---------------End of Original Message-----------------


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> -----Original Message-----
> From: TC [mailto:trclark@shaw.ca]
> Sent: October 12, 2004 11:06 AM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: Re: [Asterisk-Users] Chaining more than one zap echo 
> canceller?
> 
> 
> - I am very close to my serving CO which brings the line down to about
> 150ohms and the channel bank is expecting 600ohms.
{clip}
> where/how did you measure this ?
This was measured out of the distribution frame at the CO by a telco cable
technician.
> >  So, I have a fix for the sidetone/impedance problem (PRI on order)
{clip}
> heh looks like your in BC, is replacing with  a pri cost effective in my
> calc's here the break pt is usually about 16-18 analog lines ?
We have both overline and DID facilities that we are consolidating onto the
PRI. Combined with the addition of CallerID services, the ability to
reassign existing analog numbers as DID numbers and our contract discounts
it works out economical for us to implement as 11B+D at this site. The costs
for adding facilities later are pretty scary though.

For those who may be interested prices for all of Telus offerings can be
gleaned from their tariff documents at:
http://about.telus.com/cgi-bin/tariffs.cgi
> > is it possible to insert another can into the system somehow?
> some of us that have been around the block a few times with this fscking
> echo echo echo
> have ended up buying an inline hardware echo can between the T1xx/T4xx
> and the channel bank then turn off all echo cans in asterisk
> i have used the Tellab 2572 64ms and have crystal clear sound 
> others report the same
I think I'm going to end up going down this road also as I have other sites
where PRI would not be economical at all.

You're refering to inserting artificial resistance on just the tip -
wouldn't that introduce a longitudinal imbalance between tip & ring? 
> -----Original Message-----
> From: Chad Scott [mailto:chad@idworld.net]
> Sent: October 12, 2004 11:33 AM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: Re: [Asterisk-Users] Chaining more than one zap echo 
> canceller?
> 
> 
> If you're certain it is an impedance problem and the 
> impedance of your 
> line is lower than that of the CO, you can increase the impedance of 
> your line by putting a potentiometer in-line and adjusting it 
> until the 
> sidetone disappears.  This is a bare-bones solution and decreases the 
> efficiency of the line because you're putting in pure resistance.
> 
> If your impedance is higher than the CO, or if you want to be more 
> efficient, you'll need a more complicated impedance matching network.
> 
> On Oct 12, 2004, at 10:26 AM, Kris Boutilier wrote:
> 
> >  I have Asterisk connected to a channel bank via a t100p card. There
> > excessive sidetone generated on the analog side due to an impedance 
> > mismatch
> > - I am very close to my serving CO which brings the line 
> down to about
> > 150ohms and the channel bank is expecting 600ohms. However, 
> the very 
> > loud
> > sidetone is being fairly effectively supressed by the zap echo 
> > canceller and
> > I have quite usable lines as a result.
{clip}

To be clear then, my subscriber loop may have a DC resistance of 150ohms due
to the physical loop length but should have an AC impedance of 600ohm (+/- a
few)? I have to assume that as the telco cable guy was performing the test
he's telling me the AC impedance.

If so, then would I need to insert some sort of complex impedance network to
build out a match rather than just a single resistor?
> -----Original Message-----
> From: Rich Adamson [mailto:radamson@routers.com]
> Sent: October 12, 2004 2:58 PM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: Re: [Asterisk-Users] Chaining more than one zap echo 
> canceller?
> 
> 
> Adding resistance to one side of the line only begs for problems
> as it creates a tip-ring imbalance that will "cause" echo, etc,
> when other imperfections exist.
> 
> If that approach works at all for anyone, its addressing a symptom
> and not the root cause.
> 
> Try this one: Each customer loop is made up of copper and the longer 
> the copper, the more resistance. Yet the impedance (in the US) is
> consistently 600 ohms. A short loop might be a 100 ohms while a long
> loop might be well over 1500 ohms; still both are 600 ohm impedance.
> 
> ------------------------
> 
> > Impedance is the measure of total opposition (resistance, 
> capacitance, 
> > and inductance) to alternating current flow.  Adding 
> resistance will 
> > raise the impedance of the line.
> > 
{clip}