Option on_route_error defines what to do when an attempt to route a call resulted in an error, which is thrown by the Tserver to URS. If you are used to logs, you will find the EventError after RequestRouteCall.
Possible choices include:
default – Route the call to default destination
ignore – Ignore the error
delete – Delete the call from URS memory
reroute – Repeat the request
try_other – Find another target