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

[John McEntee]

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