[asterisk-users] Echo problems on ISDN. (mainly incoming call s)

[Ron Wellsted]

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Colin Anderson wrote:
> what happens when you drop your gains? use /etc/asterisk/zaptel.conf and
> fiddle with tx and rx values. Works, most of the time. 
> 
> -----Original Message-----
> From: John McEntee [mailto:john at mcentee87.freeserve.co.uk]
> Sent: Wednesday, October 11, 2006 12:25 PM
> To: Asterisk Users Mailing List - Non-Commercial Discussion
> Subject: [asterisk-users] Echo problems on ISDN. (mainly incoming calls)
> 
> 
> OK I have been battling with echo problems with asterisk on ISDN for a 
> few weeks now, and still can't solve it (although I think I have tried 
> everything I can find.)
> 
> I will try a post everything I think is possibly relevant that I can 
> remember with the hope someone can point me in the right direction.
> 
> current spec I am using (Trixbox 1.0 was still in beta at the time an 
> didn't detect the TE110 card, and modules didn't load properly when I 
> tried manually either )
> 
> Asterisk at home 2.8
> Wildcard TE110P ISDN PRI card (set to E1, I live in the UK)
> Telewest Q931 ISDN connection (currently 8 lines 100 phone numbers)
> dell SC1425 server (3.2 Ghz, 512MB, 80GB)
> SIP phones aastra 9133i run 1.4.0 firmware.
> 
> This is on a live system with about 50 users. (I have a identical system 
> for DR so can easily test out of hours)
> 
> Most the time there is no echo,
> If I phone my wife (on a normal telewest analog line) I get a slight 
> echo (fairly quiet) that she does not noticed. This happens on other 
> phone calls but the user can tolerate this (would prefer to solve it)
> 
> If a big customer (one with several thousand employees) phones me, I can 
> hear a very loud echo with an annoying delay (0.5-1.0 sec, ish), which 
> the users cannot tolerate. The customer does not get the echo, currently 
> the user phones back?
> 
> Any suggestion on How to solve the echo problems?
> 
> I have tried with echo cancellation at 800 and changing the RX and TX 
> gains to no effect. I have read that ISDN should not have echo problems 
> and that may I sould ask about the gains on the line provided by the 
> telco. Can anyone give me more information about this as if I phone 
> Telewest I want to pretend that my PBX supplier has told me to ask XXX. 
> As the first thing they ask me is to contact my my PBX supplier (I had a 
> slight problem getting the ISDN card to initially connect)
> 
> 
> Thanks
> 
> John

I have found that Telewest are terrible for echo.  If a one of the
endpoints is on a Telewest system, we get echo (with latency), no matter
if the other end point is via BT or Sipdiscount.  We often call or are
called by people who are on TW centrex systems and get exactly the sort
of echo you describe, it does seem to be worst on inbound calls (TW -> BT).


- --
Ron Wellsted
ron at wellsted.org.uk http://www.wellsted.org.uk
N 52.567623, W 2.137621 Linux Counter No. 202120
FWD:519961
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