A Byzantine Fault-Tolerant and Self-Stabilizing Protocol

for distributed clock synchronization systems
A distributed system is defined to be self-stabilizing when it can come from an arbitrary state and be in the presence of a bounded number of Byzantine faults, yet be guaranteed to reach a legitimate state in a finite amount of time and remain there as long as the number of faults are within a specific bound. (The legitimate state is a state where all good clocks in the system are synchronized within a given precision bound.) The self-stabilization problem is both event-driven and time-driven. Most attempts on solving the problem to date have focused only on the event-driven aspect. The NASA protocol presented here merges both the time- and event-driven aspects in order to self-stabilize the system in a gradual yet timely manner. Furthermore, this protocol is based on a continual vigilance of the state of the system to maintain and guarantee its stabilized status. Finally, initialization and/or reintegration are regarded as inherent parts of this self-stabilizing protocol, and are not treated as special cases. A simplified model of the protocol has been model-checked and has proven to self-stabilize in the presence of one permanent Byzantine faulty node with arbitrarily malicious behavior.
NASA's Langley Research Center researchers have developed and verified an approach to creating a self-stabilizing and Byzantine fault-tolerant protocol for distributed clock synchronization systems. Distributed computing systems are finding increasing usage in applications where individual nodes are operating independently, yet are linked into and serving the needs of a larger, more complex system. Clock synchronization is an example of a critical function for many distributed systems, and thus, fault tolerance and self-stabilization of clock synchronization are of key importance.

Self-stabilizes a distributed
system of nodes from an
arbitrary state


Embedded systems

Distributed process control

Computer networks

Internet and Internet applications

Security and safety

Automotive and other transport

Telecommunication and other
communication systems

Patent Number: 
Internal Laboratory Ref #: 
Patent Status: 
Patent Issue Date: 
May 6, 2015
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