[cisco-voip] FXO and auto busyout?

[Auralythic]

Good day, all,

Please bear with me, I do consider myself very "green" with VoIP. We
use FXOs for E911 purposes on 3825s and 3925s. We have VIC2-4FXO cards
in each router. Some are full routers, some are just voice gateways.
We used to run various releases of ios 12 spservicesk9 on 3825s. If
the analog line would go down, either due to a bad cross-connect or a
failure on the provider's end, we would have to busy out the port
ourselves. We had the ability to purchase new 3825s and I began to
experiment with ios upgrades. This new batch received a release of ios
15.1 ipvoice. I noticed that this ios would automatically busy out a
port on the FXO if the FXO detected the line was down. This was
fantastic. Some of our sites still needed spservices and they received
15.1 releases with spservices. We are running 3825s with 15.1.4M3
spservices, 15.1.4M ipvoice, a few 3825s still with ios 12 spservices
(hardware limitations) and now some 3925s with spservices and either a
release of 15.0 or 15.1.4M or 15.1.4M3.

My question lies in figuring out why the 3825s with ios 15 ipvoice
will apparently busyout FXO ports on its own and why a 3925 running
ios 15.1.4M3 spservices is NOT busying out an FXO port when I verified
the line is indeed dead at the demark. Is there a difference in
ipvoice and spservices? I could be wrong, but I thought spservices
included everything ipvoice does.

Thank you!

-Diana