[Asterisk-Users] Current echo status?

[echo-asterisk at secondphone.com]

On Thu, Jul 15, 2004 at 08:34:18PM -0600, Rich Adamson wrote:
> > I've been following the list for months, and I have a working Asterisk 
> > setup, but it'd be *really* useful to me at this point if someone could 
> > summarize when Asterisk has echo problems and when it doesn't.  For 
> > instance, I usually hear a far-end echo when talking on my 7940, but 
> > not when using a POTS phone plugged into a TDM400 FXO port.  It doesn't 
> > seem to matter if the call goes out over a POTS line or via NuFone; 
> > either way there's a fair bit of echo on most (but not all) calls.
> > 
> > Do different SIP phones have better echo cancellation then the Cisco 
> > 7940/60s?  How about the Polycom IP500/600s?
> > 
> > Does it matter if calls go out via POTS/T-1/PRI/VoIP?
> > 
> > The general impression that I've received is that "fast" channels 
> > (basically traditionally telephony interfaces) don't exhibit noticeable 
> > echo, but the slight delay associated with VoIP packetization unmasks 
> > existing echo.  Is that a reasonable summary?
> > 
> > We're starting to plan for a new office build-out at work, and I'd love 
> > to use Asterisk and SIP phones in the new office, but I'm not going to 
> > try to sell management on a phone system with a horrible echo problem, 
> > even if it will get fixed eventually.
> 
> For the most part, echo is less of a problem today then what it was
> a month or so ago. The source of the echo varys case by case, however
> key points that need to be addressed in _any_ installation include:
>  - * fxo pstn interface cards (eg, x100p, tdm-fxo) have to be configured
>    to match the impedance of the telco standard for whatever country
>    you're in. The x100p, by design, appears to be limited to a 600 ohm 
>    telco impedance (US standard), and will likely generate echo when
>    attached to pstn lines that are not 600 ohms. The tdm cards are
>    different and can be configured to match just about any telco standard
>    worldwide. (Don't know about the x101p, never seen one.)
>  - echo issues with the zap interfaces (eg, x100p, tdm, T1/E1 cards)
>    rely on a software echo canceler within asterisk. If the above
>    impedance match is correct, most implementations seem to have found
>    parameters that minimize echo for them. However, there are still some
>    in which echo is a problem and best 'guess' as of this afternoon is
>    those cases appear to have something to do with undocumented internal 
>    system hardware. Some folks have found swapping a motherboard for
>    another with no other changes reduces echo by noticable amounts.
>    That would suggest buss speed, PCI version, or something like that
>    other then processor speed or RAM. There are working examples of
>    300 mhz machines with no echo, 2.2 ghz machines with echo, and dual
>    processor systems with echo.
>  - Digital interfaces to * (eg, T1/E1, PRI, ISDN) tend to be less prone
>    to echo, however there are some implementations that still have it
>    and non-technical users of those systems do complain. Technical
>    users tend to tune it out.
>  - there has been very little list noise associated with echo that 
>    could be honestly pinned on any sip phone.
>  - there's been a lot of opinions stated about the cause of echo on 
>    the list, and at least some have no technical factual basis.
>  - there's a rather strong belief that additional echo problems exist
>    within asterisk, and a group of non-programmer types are attempting
>    to isolate common items in an effort to document the problem for
>    those that have the programming skills to address. (That's happening
>    on a non-asterisk email list.)
> 
> It seems that production systems either don't have any echo issues, or
> they have objectionable amounts. There does not seem to be anything
> in between. Its probably fair to say the majority (if no all) developers
> don't have the problem, making it most difficult to isolate and
> troubleshoot the cause.
> 
> Best guess (based only on the list noise level since Octomber 2003) is
> that probably 80% of the production * systems are near echo free, and
> 20% still have objectionable echo. Others may argue a different ratio. 
> YMMV.
> 
> Rich
> 

Well, I must be among that 20%.  I have annoying echo on PRI lines and
have tried everything available to mitigate the problem, with no
success.

I am a programmer with sufficient technical skills to attack the
problem.  HOWEVER, I am not about to spend the time it would take to
decipher zaptel.c all by myself.

I OFFER to PAY someone who has an understanding of zaptel.c to help me
with this problem.  Any takers out there???

echo at secondphone.com



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