Fault-tolerant clock synchronization in distributed systems

Abstract

igital computers have become essential to critical real-time applications such as aerospace systems, life support systems, nuclear power plants, drive-by-wire systems, and computer-integrated manufacturing systems. Common to all these applications is the demand for maximum reliability and high performance from computer controllers. This requirement is necessarily stringent because a single controller failure in these applications can lead to disaster. For example, the allowable probability of failure for a commercial aircraft is specified to be less than per 10-hour mission because a controller failure during flight could result in a crash.Because of such stringent requirements, traditional methods for design and validation of computer controllers are often inadequate. Ad hoc techniques that appear sound under a careful failure-modes-andeffects analysis are often susceptible to certain subtle failure modes. The clock synchronization problem shown in Figure 1 is a classic example. The figure shows a three-node system in which each node has its own clock. The clocks are synchronized by adjusting each to the median of the three Figure 1 b the faulty clock B reports incorrectly to clocks A and C. As a result, clocks A and C do not make any corrections because both behave as if they are the median clock. Lamport and Melliar-Smith were the first to study the three-clock synchronization problem in the presence of arbitrary fault behavior.' They coined the term Byzantine fault to refer to the fault model in which a faulty clock can exhibit arbitrary behavior including, but not limited to, misrepresenting its value to other clocks in the system. They showed that in the presence of Byzantine faults, no algorithm can guarantee synchronization of the nonfaulty clocks in a three-node system. They also showed that 3m + 1 clocks are sufficient to ensure synchronization of the nonfaulty clocks in the presence of m Byzantine faults. This condition later proved not only sufficient but also necessary for ensuring synchronization in the presence of Byzantine faults.Since the initial study by Lamport and Melliar-Smith, the problem of clock synchronization in the presence of Byzantine faults has been studied extensively by several other researchers. All this attention is mainly beOctober 1990 @@18~91h?i9Oll0@@-0033$@1.00 G 1990 IEEE

Research Overview of Clock Synchronization in Wireless Sensor Network

“…TSync algorithm adopts dual-channel the method combines the broadcast, synchronization mechanism and the message bidirectional exchange model algorithm, and the communication overhead is small. But it assumes that each node knows its underlying neighboring node ID number, which is a problem that needs to be solved in the actual synchronization [35]. "For some applications that do not require high precision, but require low computational complexity, consider using DMTS.…”

MuON: Epidemic based mutual anonymity in unstructured P2P networks

“…Clocks may be synchronized in hardware, software, or some hybrid combination [32][33][34]. The increasing availability of global positioning system (GPS) based hardware allows physically dispersed systems to be synchronized [35] with a clock skew of a few microseconds 4 via their mutual synchronization to Coordinated Universal Time (UTC).…”

A Runtime Stability Analysis of Clock Synchronization Precision on a Time-Triggered Bus Prototype

“…For a more deep discussion in this subject the reader is referred to (Lamport and Melliar-Smith, 1985), (Srikanth and Toueg, 1987), (Ramanathan et al, 1990) and (Schneider, 1986). In this section, only the fundamental principles applicable to TDMA-based systems are reviewed and basic notation is provided.…”