The Reboot RPC is used by the ACS to explicitly cause the device hardware to restart. This could be for any number of reasons, though should never be used as a means to force the CPE to upgrade itself. The Reboot RPC takes only one argument - CommandKey - used as it is elsewhere. The response contains no arguments.
When the device reboots, it must initiate a session with the ACS as soon as it is able to do so. The Inform RPC in this session contains the 1 - BOOT event, and also contains the “M Reboot” event. This tells the ACS that the session is starting because the device rebooted, and that this reboot was explicitly due to the ACS using the Reboot RPC.
The other method the ACS can use to get the CPE into a known state is FactoryReset. This optional RPC and its response have no arguments, and should be used very carefully, since “Factory Default” is not a clearly defined state, though can be used in devices known to have a default ACS configured in its system.