From Unofficial BOINC Wiki
RPC stands for Remote Procedure Call. Normally Procedure calls are made from one place in a computer program to another place in the computer program all on the same computer. A Remote Procedure Call is made from a computer program on one machine to a computer program on a different machine. In this case the function call is made from the Host computer to the Project's Scheduler. The reply to the Remote Procedure Call has information about any new settings that the Scheduler needs to send to the client and any Work Units that the Scheduler wants the Host to process.
 Scheduler RPC Triggers
- More work is needed. When more work is needed for the same Project the Scheduler RPC to request more work will also Report completed work.
- Ready To Report work is less than 24 hours from the Deadline.
- Ready To Report work has been Ready To Report longer than the Work Buffer size. First implemented in Version 4.43, but was buggy.
- To send a Trickle-message in Climateprediction.net (CPDN)
- Manually requested by the Participant.