echo cancellation / suppression in chan_capi & isdn4bsd by HPS

[Michael Iedema]

Greetings everyone,

I'm trying to understand what options are available to me regarding
echo cancellation and suppression in chan_capi and isdn4bsd from HPS
(http://www.turbocat.net/~hselasky/isdn4bsd/).

Great software, just trying to understand it a bit more thoroughly.

In the chan_capi code, I see references to:
- echo cancellation in hardware
- echo cancellation in software
- echo suppression in software

I understand the chan_capi options to mean:
- echocancel -  activates hardware echo cancellation if it is
available or software echo cancellation in the i4b driver if it is
not.
- echosquelch - activates some "light" echo cancellation in the
chan_capi code itself
- echocancelold - must be activated for older cards not supporting the
new echo cancellation method
- echotail - echo can tap count

Here's what I'm still not clear on:
- What do the g164, g165 and force options cause on the "echocancel" line?
- Are the echocancel/echosquelch options smart enough to only be
activated if the "better" of the two is already activated?
- Is there a way to tell if a card needs "echocancelold" to be set?
- What is the value range for "echotail"? (32, 64, 128, 256?)

Thanks in advance for any feedback on this.
-Michael I.