RADIUS accounting can be used for two purposes:
CLI command accounting
Enhanced Subscriber Management subscriber host accounting
The RADIUS accounting application tries to send all the accounting records of a subscriber host to the same RADIUS server. If that server is down, then the records are sent to the next server, and from that moment on, the RADIUS application uses that server as the destination for accounting records for that subscriber host. Enhanced Subscriber Management applies to the 7750 SR platform.