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tntknight at gmail.com
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Posted: Tue Mar 17, 2009 12:03 am Post subject: [Freeswitch-users] echo cancellation on PRI cards

I'm thinking about doing a project that would use FreeSWITCH as an IVR, with callers being routed in by both ISDN PRI, and also SIP trunks, with occasional bridge calls between callers. I'm wondering in what use cases hardware echo cancellation on the PRI cards is needed. And does hardware echo cancellation work with OpenZap/FreeSWITCH? It looks like all the major cards (Sangoma, Digium, etc..) use Octasic Echo cancellation add-on cards. Is there any difference between brands? Any recommendations on PRI boards and whether I need to pay for echo cancellation are appreciated Thanks. Tony

krice at freeswitch.org
Guest

Posted: Tue Mar 17, 2009 12:46 am Post subject: [Freeswitch-users] echo cancellation on PRI cards

The cards that feature Hardware Echo Can’s work on hardware/driver level and are supported... From: Anthony Knight <tntknight@gmail.com> Reply-To: <freeswitch-users@lists.freeswitch.org> Date: Tue, 17 Mar 2009 00:55:35 -0400 To: <freeswitch-users@lists.freeswitch.org> Subject: [Freeswitch-users] echo cancellation on PRI cards I'm thinking about doing a project that would use FreeSWITCH as an IVR, with callers being routed in by both ISDN PRI, and also SIP trunks, with occasional bridge calls between callers. I'm wondering in what use cases hardware echo cancellation on the PRI cards is needed. And does hardware echo cancellation work with OpenZap/FreeSWITCH? It looks like all the major cards (Sangoma, Digium, etc..) use Octasic Echo cancellation add-on cards. Is there any difference between brands? Any recommendations on PRI boards and whether I need to pay for echo cancellation are appreciated Thanks. Tony _______________________________________________ Freeswitch-users mailing list Freeswitch-users@lists.freeswitch.org http://lists.freeswitch.org/mailman/listinfo/freeswitch-users UNSUBSCRIBE:http://lists.freeswitch.org/mailman/options/freeswitch-users http://www.freeswitch.org

wasim at convergence.pk
Guest

Posted: Tue Mar 17, 2009 12:55 am Post subject: [Freeswitch-users] echo cancellation on PRI cards

2009/3/17 Anthony Knight <tntknight@gmail.com (tntknight@gmail.com)>

Quote:

I'm thinking about doing a project that would use FreeSWITCH as an IVR, with callers being routed in by both ISDN PRI, and also SIP trunks, with occasional bridge calls between callers.

I'm wondering in what use cases hardware echo cancellation on the PRI cards is needed.

When there is Echo being generated from the far end, usually in a bridged call. If you application is just an IVR, with no far end connectivity, then you shouldn't need an echo can. If you are bridging calls, then at some point you may need it, depending on what else is in the loop.

Quote:

And does hardware echo cancellation work with OpenZap/FreeSWITCH?

Yes, it really has nothing to do with the software then, its handled by the card and its hardware driver. In Sangoma's case, by Wanpipe.

Quote:

It looks like all the major cards (Sangoma, Digium, etc..) use Octasic Echo cancellation add-on cards. Is there any difference between brands?

Sangoma has 1024 tap Octasic Echo Cans. Very nice they are indeed.

Quote:

Any recommendations on PRI boards and whether I need to pay for echo cancellation are appreciated

Unashamedly, Sangoma's. 100% of the cases where our customers have used Sangoma A10Xd vs A10X, they've been much happier with the quality on the line. Its a tad bit more $, but well worth it (especially in places with bad copper).

--

wasim h. baig | principal consultant | convergence pk | +92 300 8508070 | peace be upon you ...

steveu at coppice.org
Guest

Posted: Tue Mar 17, 2009 7:22 am Post subject: [Freeswitch-users] echo cancellation on PRI cards

Wasim Baig wrote:

Quote:

2009/3/17 Anthony Knight <tntknight@gmail.com
<mailto:tntknight@gmail.com>>

I'm thinking about doing a project that would use FreeSWITCH as an
IVR, with callers being routed in by both ISDN PRI, and also SIP
trunks, with occasional bridge calls between callers.

I'm wondering in what use cases hardware echo cancellation on the
PRI cards is needed.

When there is Echo being generated from the far end, usually in a
bridged call. If you application is just an IVR, with no far end
connectivity, then you shouldn't need an echo can. If you are bridging
calls, then at some point you may need it, depending on what else is
in the loop.

This is VERY VERY WRONG. IVRs badly need echo cancellation. Without it
they give very poor reliability detecting DTMF while the prompts are
playing. If the system uses voice recognition, its reliability will be
even worse.

Quote:

And does hardware echo cancellation work with OpenZap/FreeSWITCH?

Yes, it really has nothing to do with the software then, its handled
by the card and its hardware driver. In Sangoma's case, by Wanpipe.

It looks like all the major cards (Sangoma, Digium, etc..) use
Octasic Echo cancellation add-on cards. Is there any difference
between brands?

Sangoma has 1024 tap Octasic Echo Cans. Very nice they are indeed.

Any recommendations on PRI boards and whether I need to pay for
echo cancellation are appreciated

Unashamedly, Sangoma's. 100% of the cases where our customers have
used Sangoma A10Xd vs A10X, they've been much happier with the quality
on the line. Its a tad bit more $, but well worth it (especially in
places with bad copper).

If you use Sangoma make sure everything is up to date. People have had a
lot of DTMF detection trouble with some revisions of the driver, or on
board firmware, or possibly both. Clearly DTMF trouble would be pretty
bad for an IVR. I didn't manage to trace which were the offending
versions, but the current stuff is apparently OK.

Steve

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dave at 3c.co.uk
Guest

Posted: Tue Mar 17, 2009 10:17 am Post subject: [Freeswitch-users] echo cancellation on PRI cards

Steve Underwood wrote:

Quote:

When there is Echo being generated from the far end, usually in a
bridged call. If you application is just an IVR, with no far end
connectivity, then you shouldn't need an echo can. If you are bridging
calls, then at some point you may need it, depending on what else is
in the loop.

With respect, this is at best half true. DTMF detection has always worked just fine
without echo cancellation - the Dialogic, Aculab and Rhetorex cards which I used
in the late 1990s managed it perfectly well; if the DTMF detection code in * and FS
can't, then maybe that's something for its author to look at Wink

ASR - yes, maybe, but L&H's ASR1500 used to work perfectly well on the same
hardware above back in the day. I'd be interested to see results of testing an ASR
engine in with echo; unfortunately, most vendors appear to prohibit the publication
of test results in their licensing.

--Dave

steveu at coppice.org
Guest

Posted: Tue Mar 17, 2009 10:50 am Post subject: [Freeswitch-users] echo cancellation on PRI cards

David Knell wrote:

Quote:

Steve Underwood wrote:

Quote:

When there is Echo being generated from the far end, usually in a
bridged call. If you application is just an IVR, with no far end
connectivity, then you shouldn't need an echo can. If you are bridging
calls, then at some point you may need it, depending on what else is
in the loop.

With respect, this is at best half true. DTMF detection has always
worked just fine
without echo cancellation - the Dialogic, Aculab and Rhetorex cards
which I used
in the late 1990s managed it perfectly well; if the DTMF detection
code in * and FS
can't, then maybe that's something for its author to look at Wink

Try reading the Dialogic and Aculab documentation. Those cards used
quite a bit of their DSP capability to remove the spillback of outgoing
voice into their DTMF receivers. You'll find the DTMF detector in
spandsp (not necessarily the ones in * or FS, which have been altered a
bit) is superior to either Dialogic or Aculab's.

Quote:

ASR - yes, maybe, but L&H's ASR1500 used to work perfectly well on the
same
hardware above back in the day. I'd be interested to see results of
testing an ASR
engine in with echo; unfortunately, most vendors appear to prohibit
the publication
of test results in their licensing.

L&H used to work fine with the J series Dialogic cards. The Dialogic
documents go into considerable details about the echo cancellation
arrangements to make that happen.

Regards,
Steve

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tntknight at gmail.com
Guest

Posted: Tue Mar 17, 2009 11:47 am Post subject: [Freeswitch-users] echo cancellation on PRI cards

Thanks for the feedback.

I have plenty of experience with IVRs and Dialogic cards (starting with D121/LSI120s and SS96s under DOS in the 90's all the way up to Intel's DM/Vs) and didn't ever have a problem with DTMF collection with ISDN PRI lines except occasionally with wireless and cell phones (Bad line quality).

These new cards are so much cheaper than the Dialogic cards were, I should just buy the version with the cancellers.

Tony

On Tue, Mar 17, 2009 at 11:36 AM, Steve Underwood <steveu@coppice.org (steveu@coppice.org)> wrote:

Quote:

David Knell wrote:

Quote:

Steve Underwood wrote:

Quote:

When there is Echo being generated from the far end, usually in a
bridged call. If you application is just an IVR, with no far end
connectivity, then you shouldn't need an echo can. If you are bridging
calls, then at some point you may need it, depending on what else is
in the loop.

With respect, this is at best half true. DTMF detection has always
worked just fine
without echo cancellation - the Dialogic, Aculab and Rhetorex cards
which I used
in the late 1990s managed it perfectly well; if the DTMF detection
code in * and FS
can't, then maybe that's something for its author to look at Wink

Quote:

ASR - yes, maybe, but L&H's ASR1500 used to work perfectly well on the
same
hardware above back in the day. I'd be interested to see results of
testing an ASR
engine in with echo; unfortunately, most vendors appear to prohibit
the publication
of test results in their licensing.

L&H used to work fine with the J series Dialogic cards. The Dialogic
documents go into considerable details about the echo cancellation
arrangements to make that happen.

Regards,

Steve

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steveu at coppice.org
Guest

Posted: Tue Mar 17, 2009 11:48 am Post subject: [Freeswitch-users] echo cancellation on PRI cards

Anthony Knight wrote:

Quote:

You have my deepest sympathy. Smile

Steve

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dave at 3c.co.uk
Guest

Posted: Tue Mar 17, 2009 1:05 pm Post subject: [Freeswitch-users] echo cancellation on PRI cards

Steve Underwood wrote:

Quote:

David Knell wrote:

Quote:

Steve Underwood wrote:

Quote:

When there is Echo being generated from the far end, usually in a
bridged call. If you application is just an IVR, with no far end
connectivity, then you shouldn't need an echo can. If you are bridging
calls, then at some point you may need it, depending on what else is
in the loop.

With respect, this is at best half true. DTMF detection has always
worked just fine
without echo cancellation - the Dialogic, Aculab and Rhetorex cards
which I used
in the late 1990s managed it perfectly well; if the DTMF detection
code in * and FS
can't, then maybe that's something for its author to look at Wink

The first bit of that's a tad patronising, isn't it, and, in the case of the decade-old Aculab
cards which which I'm most familiar, is also untrue.

As for the second, do you have any test results to back that up? I'm more curious than
setting out for an argument..

Quote:

ASR - yes, maybe, but L&H's ASR1500 used to work perfectly well on the
same
hardware above back in the day. I'd be interested to see results of
testing an ASR
engine in with echo; unfortunately, most vendors appear to prohibit
the publication
of test results in their licensing.

L&H used to work fine with the J series Dialogic cards. The Dialogic
documents go into considerable details about the echo cancellation
arrangements to make that happen.

You've missed the point I was trying to make. It used to work fine with no echo cancellation
at all.

--Dave

steveu at coppice.org
Guest

Posted: Tue Mar 17, 2009 1:36 pm Post subject: [Freeswitch-users] echo cancellation on PRI cards

David Knell wrote:

Quote:

Steve Underwood wrote:

Quote:

David Knell wrote:

Quote:

Steve Underwood wrote:

Quote:

When there is Echo being generated from the far end, usually in a
bridged call. If you application is just an IVR, with no far end
connectivity, then you shouldn't need an echo can. If you are bridging
calls, then at some point you may need it, depending on what else is
in the loop.

With respect, this is at best half true. DTMF detection has always
worked just fine
without echo cancellation - the Dialogic, Aculab and Rhetorex cards
which I used
in the late 1990s managed it perfectly well; if the DTMF detection
code in * and FS
can't, then maybe that's something for its author to look at Wink

The first bit of that's a tad patronising, isn't it,

You are the one who started out being offensive.

Quote:

and, in the case of the decade-old Aculab
cards which which I'm most familiar, is also untrue.

I can't find too much about the old cards on the web now, but I found
http://www.amdevcomm.com/voice-mail-products/voice-mail-components/dialogic/dti_sc.html
which is pretty much a copy and paste from the old Dialogic web pages,
and you'll see it says "Cut through : Local echo cancellation permits
100% detection with a >4.5 dB return loss line". The Aculabs did the
same thing for sure. They just couldn't work without cancellation. There
were some very early Dialogic cards, using DTMF receiver chips and OKI
ADPCM chips, and had no general purpose DSPs. They performed really
badly because of the lack of cancellation, and were quickly replaced
with cards that put the OKI ADPCM, DTMF anf echo cancellation algorithms
into a Motorola 56k DSP chips.

Quote:

As for the second, do you have any test results to back that up? I'm
more curious than
setting out for an argument..

Quote:

ASR - yes, maybe, but L&H's ASR1500 used to work perfectly well on the
same
hardware above back in the day. I'd be interested to see results of
testing an ASR
engine in with echo; unfortunately, most vendors appear to prohibit
the publication
of test results in their licensing.

L&H used to work fine with the J series Dialogic cards. The Dialogic
documents go into considerable details about the echo cancellation
arrangements to make that happen.

You've missed the point I was trying to make. It used to work fine
with no echo cancellation
at all.

I think you've missed the point. These things don't work by pixey dust.
They work by engineering. If you have any old J or JCT cards around
record the signal from the far end. You'll find only the tiniest trace
of the outgoing signal mixed in with it. How do you think that happens?

Steve

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dave at 3c.co.uk
Guest

Posted: Tue Mar 17, 2009 6:31 pm Post subject: [Freeswitch-users] echo cancellation on PRI cards

Steve Underwood wrote:

Quote:

[whopping big snip]

Quote:

The first bit of that's a tad patronising, isn't it,

You are the one who started out being offensive.

I'm sorry if you find disagreement offensive; you might not wish to read beyond this
point if so.

Quote:

and, in the case of the decade-old Aculab
cards which which I'm most familiar, is also untrue.

The same document, under the bit which you've quoted, says:
"(E-1) Digital trunks use separate transmit and receive paths to network.
Performance dependent on far end handset's match to local analog loop."
- i.e. the card does no echo cancellation.

Aculab didn't even offer echo cancellation on Prosody for years and, when they did, it
consumed prodigious amounts of DSP. Nonetheless, the DTMF detection worked
perfectly well, even across 120 channels per 40MHz SHARC - there's just no way
that those DSPs had enough horsepower to do echo cancellation across that many
channels.

An Asterisk box with an el-cheapo quad E1 card in that I use for TDM-SIP gatewaying
detects DTMF perfectly well with no echo cancellation.

You just don't need echo cancellation to achieve perfectly acceptable DTMF detection.

ASR - yes, maybe, but surely only in the case where the application requires barge-in;
even then, I'd be interested to see some test results, particuarly where the outbound prompt
is killed the moment the ASR reports start of speech.

I'm afraid that your original bald claim - that "IVRs badly need echo cancellation" is simply
wrong, misleading and irresponsible: those believing it will end up spending large sums
of money on technology which they probably do not need.

--Dave

msc at freeswitch.org
Guest

Posted: Tue Mar 17, 2009 6:48 pm Post subject: [Freeswitch-users] echo cancellation on PRI cards

Quote:

I'm afraid that your original bald claim - that "IVRs badly need echo
cancellation" is simply
wrong, misleading and irresponsible: those believing it will end up spending
large sums
of money on technology which they probably do not need.

Anybody with years, perhaps decades, of DSP programming experience
plus testing in the real world - and all over the world - has my vote
of confidence. Furthermore, when this person writes spandsp, makes it
open source, and freely answers questions about it on public fora, I
am inclined not only to believe him but to trust his judgment.

Bottom line: thousands of people have chosen to heed Steve's advice.
He is well-respected in many technical communities. His reputation is
as solid as it gets. "Do what Steve says" is about the safest bet you
will ever make in this business.

-MC

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steveu at coppice.org
Guest

Posted: Tue Mar 17, 2009 7:37 pm Post subject: [Freeswitch-users] echo cancellation on PRI cards

David Knell wrote:

Quote:

Steve Underwood wrote:

Quote:

[whopping big snip]

Quote:

The first bit of that's a tad patronising, isn't it,

You are the one who started out being offensive.

I'm sorry if you find disagreement offensive; you might not wish to
read beyond this
point if so.

Quote:

and, in the case of the decade-old Aculab
cards which which I'm most familiar, is also untrue.

Your messages are starting to looked deranged. Why would they only apply
echo cancellation to T1s? Its a bizarre idea, and you must realise its
wrong. Are you so desperate to support a wrong answer you'll clutch at
straws? :-\

Quote:

Aculab didn't even offer echo cancellation on Prosody for years and,
when they did, it
consumed prodigious amounts of DSP. Nonetheless, the DTMF detection
worked
perfectly well, even across 120 channels per 40MHz SHARC - there's
just no way
that those DSPs had enough horsepower to do echo cancellation across
that many
channels.

This page
http://www.aculab.com/support/pdf_documents/v6_solaris/ting/pubdoc/an-dtmf-det-issues.html
seems to support what you say. It also implies DTMF detection sucks
unless you echo cancel. The statement "If the outgoing signal is a tone
of some sort (e.g. a 'beep'), ensure that its frequency is below 600Hz"
is telling you to keep your outgoing signal in the same frequency range
as dial-tone where the dial-tone filter on the DTMF receiver will
obviate the need for an echo canceller. They are freely admitting
exactly what I have said. If you want a normal IVR with cut-through to
work you better turn that echo canceller on.

My only experience with Aculab was fitting a box designed by other
people into a system. That one definitely echo cancelled, as it worked
as well as the Dialogic based boxes we developed ourselves.

Quote:

An Asterisk box with an el-cheapo quad E1 card in that I use for
TDM-SIP gatewaying
detects DTMF perfectly well with no echo cancellation.

You must have very low standards for "works well".

Quote:

You just don't need echo cancellation to achieve perfectly acceptable
DTMF detection.

Well, not if you expect people to wait for silence before entering DTMF,
but who would tolerate that these days? Cut through has been de rigeur
since the late 80s.

Quote:

ASR - yes, maybe, but surely only in the case where the application
requires barge-in;
even then, I'd be interested to see some test results, particuarly
where the outbound prompt
is killed the moment the ASR reports start of speech.

Doesn't any sane system expect barge in to be nearly as reliable as
waiting for silence? Who would tolerate something that doesn't? It has
been a standard expectation of any decent IVR since they began.

Quote:

I'm afraid that your original bald claim - that "IVRs badly need echo
cancellation" is simply
wrong, misleading and irresponsible: those believing it will end up
spending large sums
of money on technology which they probably do not need.

You must have very low standards for what works well. If you suggest
people leave out echo cancellation you are just asking for customer
service issues down the line. That whole Aculab page is a clear response
to just such issues they had, which forced them to add the necessary
improvements.

Regards,
Steve

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dave at 3c.co.uk
Guest

Posted: Tue Mar 17, 2009 9:11 pm Post subject: [Freeswitch-users] echo cancellation on PRI cards

Steve Underwood wrote:

Quote:

David Knell wrote:

Quote:

Steve Underwood wrote:

Quote:

[whopping big snip]

Quote:

The first bit of that's a tad patronising, isn't it,

You are the one who started out being offensive.

I'm sorry if you find disagreement offensive; you might not wish to
read beyond this
point if so.

Quote:

and, in the case of the decade-old Aculab
cards which which I'm most familiar, is also untrue.

More insults. Answer me this: if there were echo cancellation in use, why would
DTMF detection performance depend on the far-end handset's match to the loop?

And the follow-up question (which you've already pretty much asked) - if the
card doesn't echo cancel for E1s, why would it for T1s?

As an aside, I'm not convinced that the document's not talking about return loss
on the T1 line itself, the implication being that the T1 is being carried on a single
pair, which makes the first sentence about E1s make a bit more sense. But that's
just a guess.

Quote:

Steve Underwood wrote:

0 Steve Underwood wrote:

That only holds true if your premise - that you need echo cancellation for good
DTMF detection - is correct, which I don't believe it is.

Quote:

Steve Underwood wrote:

2 Steve Underwood wrote:

Nothing like a good old ad hominem attack. Beats reasoned argument any day.

Quote:

Steve Underwood wrote:

4 Steve Underwood wrote:

Oh, for pity's sake, you get perfectly good cut through without echo cancellation.
Humour me and draw a quick mental picture of the spectrum of a random bit of
speech at -20dBm; now add tones at -10dBm and -7dBm. They stick out like
a pair of sore thumbs.

I'm sure it's quite possible to come up with a pathological case - e.g. cut-through
against a 1kHz milliwatt tone, but that sort of thing just doesn't happen in real-
life IVR applications.

Quote:

Steve Underwood wrote:

6 Steve Underwood wrote:

Sorry - ASR with barge-in has been a standard expectation since the first IVRs?

Quote:

Steve Underwood wrote:

8 Steve Underwood wrote:

egghunt at gmail.com
Guest

Posted: Tue Mar 17, 2009 9:48 pm Post subject: [Freeswitch-users] echo cancellation on PRI cards

Sharing my humble experience: in Brazil we usually need echo cancellation to have reliable DTMF detection _and_ voice quality over E1 lines (be it on MFC/R2 - r2d - or ISDN PRI lines), either for sip/tdm gateway devices or IVR applications.

Usually there's no need for echo cancellation on links from some Telcos, in some specific places. But we need it in the majority of cases, even when my box is just a gateway between legacy pbxes.

This represents just a subset of the available E1s in the world and it's just a practical experience, but it's a fact for me. If I don't have a card with echo cancellation, I don't offer reliability to my customer; I've done that in the past and didn't work out.

I'm not theoretically discussing anything, just sharing what I've been through in the last 4 or 5 years.

2009/3/17 David Knell <dave@3c.co.uk (dave@3c.co.uk)>

Quote:

Steve Underwood wrote:

Quote:

David Knell wrote:

Quote:

Steve Underwood wrote:

Quote:

[whopping big snip]

Quote:

The first bit of that's a tad patronising, isn't it,

You are the one who started out being offensive.

I'm sorry if you find disagreement offensive; you might not wish to
read beyond this
point if so.

Quote:

and, in the case of the decade-old Aculab
cards which which I'm most familiar, is also untrue.

Quote:

Steve Underwood wrote:

0 Steve Underwood wrote:

That only holds true if your premise - that you need echo cancellation for good
DTMF detection - is correct, which I don't believe it is.

Quote:

Steve Underwood wrote:

2 Steve Underwood wrote:

Nothing like a good old ad hominem attack. Beats reasoned argument any day.

Quote:

Steve Underwood wrote:

4 Steve Underwood wrote:

Quote:

Steve Underwood wrote:

6 Steve Underwood wrote:

Sorry - ASR with barge-in has been a standard expectation since the first IVRs?

Quote:

Steve Underwood wrote:

8 Steve Underwood wrote:

Repeating you ad-hominem really doesn't make it any stronger, I'm afraid. And
the Aculab page you refer to offers four solutions for problems caused by far-
end echo, of which cancellation is just one; not playing a stationary tone above 600Hz
is another.

Do you have any real-world samples of DTMF+echo which give your DTMF
detection code trouble?

--Dave

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Arnaldo M Pereira

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