qPALS: Quality-aware synchrony protocol for distributed real-time systems

Woochul Kang, Lui Sha

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish (US)
Pages (from-to)3361-3377
Number of pages17
JournalKSII Transactions on Internet and Information Systems
Issue number10
StatePublished - Oct 31 2014


  • Cyber physical systems
  • Feedback control
  • GALS
  • Globally asynchronous locally synchronous
  • Middleware
  • QoS
  • Quality-of-service
  • Real-time systems
  • Synchrony protocol

ASJC Scopus subject areas

  • Information Systems
  • Computer Networks and Communications


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