[asterisk-users] echo with spa-3000

[James Harper]

More an echo algorithm question than a purely asterisk one...

I have the following setup:

Handset - PAP2 - Asterisk - SPA3000 - Telco

And no matter what I do, I get echo on a call routed out via the PSTN
when I talk into the handset, in the order of a hundred ms (my estimate,
could be wildly inaccurate!). Echo will occur also when I have a handset
plugged into the phone port on the SPA3000 (only when the call is routed
via SIP of course), but I think it's more noticeable on the PAP2 due to
the increased latency.

The echo occurs even when I call an automated voice service or
something, so I'm thinking that possibly there is a gross impedance
mismatch on my side of the telco switch. I believe the following is
happening (latency measures are guesses):

Handset -(0ms)- PAP2 -(40ms)- Asterisk -(40ms)- SPA3000 -(0ms)- Telco

Does an EC algorithm need a measurable delay to work? The EC would have
to cope with an almost unmeasurably small echo delay (the delay only
creeps in on the other side of the IP link. Is there another way I
should be solving this problem, especially as I can keep Asterisk in the
loop if I want to?

Thanks

James