Byzantine-Resistant Total Ordering Algorithms

AbstractMulticast group communication protocols are used extensively in fault-tolerant distributed systems. For many such protocols, the acknowledgments for individual messages define a causal order on messages. Maintaining the consistency of information, replicated on several processors to protect it against faults, is greatly simplified by a total order on messages. We present algorithms that incrementally convert a causal order on messages into a total order and that tolerate both crash and Byzantine process faults. Varying compromises between latency to message ordering and resilience to faults yield four distinct algorithms. All of these algorithms use a multistage voting strategy to achieve agreement on the total order and exploit the random structure of the causal order to ensure probabilistic termination

Probabilistic Analysis of Real-Time Dependable Systems

The design of real-time dependable systems is dominated by the need to meet real-time deadlines. In this paper we present a methodology for analyzing durations in real-time dependable systems and for estimating the probabilities that real-time deadlines will be met. The probability density functions for the durations of composite operations are obtained by convolving the probability density functions for the durations of simpler operations. These probability density functions may be correlated, and such correlations must be handled correctly when the convolutions are performed. Example applications of the methodology are given for the Totem multicast group communication protocols. Keywords: Real-time, dependable, probability density function. 1 Introduction Traditionally, real-time systems have been defined by requirements that specific events, typically input or output operations, must occur at or before precisely defined moments in time [2, 4, 7, 8, 17, 18, 19, 21]. The existing m..

Global Causal Ordering with Minimal Latency

Causally order delivery of messages is a useful property for coordinatingthe activities of processors in a distributed system and for maintaining the consistency of replicated information. Timestamps in the messages can be used to impose a causal order on the delivery of messages using logical clocks or physical clocks. However, systems based on logical clocks experience a latency to message delivery that is larger than the channel latency between the most distant nodes in the system, which can be significant for systems spread over wide areas. In this paper, we present a protocol that delivers messages in system-wide causal order almost immediately after receipt, avoiding the additional latency due to causal ordering before delivery. The protocol is based on synchronized clocks, and assumes that the skew between any two clocks is less than the channel latency between the most distant nodes. Key words: Causal order, clock synchronization, latency, multicast, network protocol, wide-are..

Object-Oriented Programming of Complex Fault-Tolerant Real-Time Systems

The challenge is to build, on top of standard operating systems, complex fault-tolerant real-time systems that operate fast enough to meet real-time deadlines even under fault conditions, using an approach that simplifies the application programming. The Realize system, being developed at the University of California, Santa Barbara, aims to meet that challenge. 1 Introduction Research and design paradigms for real-time systems have focused primarily on hard real-time systems. For relatively simple preplanned synchronous systems, effective strategies have been devised that aim to guarantee real-time deadlines using worst-case workloads and worst-case performance measures. Unfortunately, complex real-time systems involve considerable uncertainty. There is variation in processor performance resulting from caches, cycle stealing, and interrupt handling; there is variation in the execution of the programs caused by many special cases and heuristic algorithms; there is variation in message ..