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ROBUS-2 Protocol Processor (RPP) is a custom-designed hardware
component implementing the functionality of the ROBUS-2 fault-
tolerant communication system. The Reliable Optical Bus (ROBUS)
is the core communication system of the Scalable Processor-
Independent Design for Enhanced Reliability (SPIDER), a general-
purpose faulttolerant integrated modular architecture currently
under development at NASA Langley Research Center.  ROBUS is a
time-division multiple access (TDMA) broadcast communication
system with medium access control by means of time-indexed
communication schedule. ROBUS-2 is a developmental version of
the ROBUS providing guaranteed faulttolerant services to the
attached processing elements (PEs), in the presence of a bounded
number of faults. These services include message broadcast
(Byzantine Agreement), dynamic communication schedule update,
time reference (clock synchronization), and distributed
diagnosis (group membership). ROBUS a