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Ratatoskr wide-area actuator RPC over gridstat with timeliness, redundancy, and safety
The development of the communication infrastructure for the north-American electrical powergrid has failed to fully incorporate important developments in the field of computer science,affecting the stability and efficiency of the power grid as a whole. The current power-gridcommunication standard, SCADA, utilizes protocols specialized for centralized communication,hampering communication between field sites key for envisioned improvements of power gridsafety and efficiency. Further, a number of different proprietary communication protocols are inuse, making communication between power utility companies very difficult.GridStat is a communication infrastructure designed for a power grid environment that solvesmany of the problems with the current situation. GridStat uses a specialization of thepublish-subscribe middleware paradigm, status dissemination, that takes advantage of thesemantics of status data to provide flexible acquisition of power-grid data with multipledimensions of QoS semantics. The middleware approach enables communication betweenutilities independent of proprietary network protocols, and allows enhanced network features such as forwarding data through multiple redundant paths. While GridStat provides excellent support for data acquisition, the publish-subscribe architecture supports only one-way communication and provides syntax and semantics unsuitable for control communications.This thesis presents Ratatoskr, a novel scheme for control of actuators using GridStat communication. It constructs a two-way communication channel on top of GridStatpublish/subscribe paths, and utilizes the QoS semantics and middleware properties GridStatprovides. For control communication Ratatoskr uses remote procedure call (RPC), providingprogrammer friendliness and familiarity. The QoS semantics of GridStat are drawn upon toprovide the timeliness required for power-grid operation. Reliability concerns are addressed byproviding three redundancy schemes, ACK/resend, transmitting multiple copies of a singlepacket, and spatial redundancy through GridStat’s redundant routing paths feature. Additionally,pre- and post-condition expressions over GridStat status variables are built into call semantics.The architecture and design of Ratatoskr is presented, along with results from an evaluation of aprototype implementation