| Summary: | 博士 === 國立中興大學 === 資訊科學與工程學系 === 96 === Reliability is an important research topic of distributed systems. To achieve fault-tolerance in the distributed systems, healthy processors need to reach a common agreement before performing certain special tasks, even if faults exist in many circumstances. This problem is called as the Byzantine Agreement (BA) problem and it must be addressed. In general, the traditional BA problem is solved in well-defined networks, such as a fully connected network or a broadcast network. However, the MANETs (Mobile Ad-hoc NETworks) are increasing in popularity and its network topology is dynamic in nature. Therefore, the BA problem and a closely related sub-problem, the Consensus problem, are re-examined in MANETs. Similarly, the dual failure mode on both processors and transmission media are considered in this dissertation.
Most BA problems require all the healthy processors to obtain an agreement at the same round; this kind of agreement is called an Immediate Byzantine Agreement (IBA). Another kind of agreement, Eventual Byzantine Agreement (EBA), allows its participants to reach a common agreement at different rounds when the f_act < f_m (f_act is the number of actual malicious faulty processors; f_m is the number of tolerate malicious faulty processors). As a result, EBA is more efficient than IBA. The EBA is also revisited in the MANET in this dissertation. Our protocol expects to use the minimum number of message exchanges to reach an agreement within the distributed system while tolerating the maximum number of faulty processors in MANETs.
As for the completeness, one important issue needs to be revised is the Fault Diagnosis Agreement (FDA). The goal of the FDA is to make each healthy processor able to detect/locate a common set of faulty processors. In general, the FDA protocol needs [(k-1)/3] + 2 (k is the number of processors in a network) rounds of message exchange to detect/locate the faulty components. However, the number of messages results in a large overhead in protocol. In this dissertation, the FDA problem is solved early by an evidence-based fault diagnosis protocol that uses the minimum number of rounds characterized by dual failure of processors. In addition, the proposed protocol can detect/locate the maximum number of faulty processors in a network.
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