qPALS: Quality-Aware Synchrony Protocol for Distributed Real-Time Systems
Woochul Kang, Lui Sha · KSII Transactions on Internet and Information Systems · 2014
Synchronous computing models provided by real-time synchrony protocols, such as TTA [1] and PALS [2], greatly simplify the design, implementation, and verification of real-time distributed systems.However, their application to real systems has been limited since their assumptions on underlying systems are hard to satisfy.In particular, most previous real-time synchrony protocols hypothesize the existence of underlying fault tolerant real-time networks.This, however, might not be true in most soft real-time applications.In this paper, we propose a practical approach to a synchrony protocol, called Quality-Aware PALS (qPALS), which provides the benefits of a synchronous computing model in environments where no fault-tolerant real-time network is available.qPALS supports two flexible global synchronization protocols: one tailored for the performance and the other for the correctness of synchronization.Hence, applications can make a negotiation flexibly between performance and correctness.In qPALS, the Quality-of-Service (QoS) on synchronization and consistency is specified in a probabilistic manner, and the specified QoS is supported under dynamic and unpredictable network environments via a control-theoretic approach.Our simulation results show that qPALS supports highly reliable synchronization for critical events while still supporting the efficiency and performance even when the underlying network is not stable.