For systems communicating over Serial0/1/0:0. Use the interface that connects to the WAN for your network.
xxx.xxx.xxx.xxx is the IP of the NCM server.
ip flow-capture ip-id
ip flow-export version 5
ip flow-export destination xxx.xxx.xxx.xxx 2055
ip flow-top-talkers
interface Serial0/1/0:0
ip flow ingress
ip flow egress