Ratatoskr: Wide-Area Actuator RPC over GridStat with Timeliness, Redundancy, and Safety
GridStat is a QoS-managed middleware framework designed to replace the power grid’s aging, inflexible, and slow data communications system. GridStat is a specialization of the publish-subscribe paradigm that takes advantage of the semantics of periodic status data updates to provide data delivery with a per-subscriber rate, latency, and redundant paths. While GridStat is well-suited for delivery of sensor data over a wide-area network, its baseline one-way mechanisms are not suitable for round-trip invocations such as setting an acutator or calling between control centers. In this paper we present the design, implementation and experimental evaluation of Ratatoskr, a tunable RPC mechanism that builds on the QoS semantics of GridStat and supports three kinds of redundancy. Additionally, user-defined pre- and post-condition predicates over GridStat status variables are built into the call semantics. Preconditions can abort an RPC call if the measured conditions dictate, while post-conditions provide additional physical
assurance the call succeeded.
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