[Asterisk-Users] X100P Echo Problems..What's going to happen?

[TC]

>Where does the 4 wire change to a 2 wire?

with just a x100p that would be at the telco in their switching gear
where they do the a/d to route the call
but if you have a channel bank withn T1 to * then you have the a/d at the
telco switch
and then again more a/d when coming off channel banks fxo to  T1 inerface in
*

you can also get echo because of a an impedance mismatch between the analog
line trunk
from the telco and the x100p (eg tip/ring reversed, incorrectly provisioning
on the analog line)

so much for theory ..:)
Now i have  questions
1)  how do you actually measure the impedance that is provisioned on the
line ??
2) what impedance does the x100 expect ??