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Quality of Time: A New Perspective in Designing Cyber-Physical Systems

  • Author(s): Anwar, Fatima Muhammad
  • Advisor(s): Srivastava, Mani B
  • et al.
Abstract

Unprecedented Cyber-Physical Systems (CPS) and Internet of Things (IoT) applications such as health care, connected vehicles, and augmented/virtual reality are revolutionizing smart spaces and change how we build and manage our systems. These applications span the cloud and the edge devices and give birth to new system designs with critical dependence on temporal use cases. As such, cloud services are expected to provide timely responses and schedulable demands, while edge devices are required to synchronize observations and choreograph actions across distributed entities. Both cloud and edge demand time awareness in general, and time-indexed queries, precise timestamping, and dynamic clock synchronization in particular. However, contemporary distributed system designs are inherently “clockless” and becoming increasingly complex. They fail to meet consistency, causality, and scheduling demands of underlying applications yet enabling time awareness for various applications running on commodity platforms and operating systems (OS) is a challenge in itself.

In this dissertation, we devise a new way of acquiring time information by introducing the notion of Quality of Time (QoT) that collectively captures various time metrics such as resolution, accuracy, stability, and integrity. Analogous to Quality of Service (QoS) in networking, QoT treats time as a controllable OS primitive with observable performance. To provide QoT to applications, we proposed the first OS abstraction – timeline – that reacts to application timing demands and exposes QoT to applications in an easy-to-use, secure, and scalable way. This degree of richness of information had never been available to coordinated applications whose activities are choreographed across time and space. This flow of information was immediately relevant to the broader field of IoT addressing the emerging temporal use cases for applications at the cloud and the edge in a secure fashion. As such, QoT expanded distributed applications to a global scale with no significant overhead and no performance compromise.

This dissertation focuses on covering various aspects of QoT. In the first part of this thesis, we design extensible abstractions to characterize timing uncertainty in the presence of timing variations. In an effort to reduce complexity and overhead of current distributed database designs, our abstractions and systems enable globally replicated lockless transactions with simplified design, low overhead and no loss in performance. The second part exposes timing vulnerabilities in trusted execution technologies and network security mechanisms and provides timing integrity by designing secure time architectures in the presence of vulnerabilities. Thus enabling trusted timestamping in commodity systems to preserve one’s digital rights and digital signals. The third part focuses on redesigning the hardware, OS and network interfaces that help time information flow between applications and systems, and enable timing precision. This precision boosts high-speed measurements at large-scale distributed entities. The final section addresses the inefficacy of testing mechanisms for time synchronization protocols deployed in safety-critical environments. We then propose a customized testbed for testing timing robustness under failures and adversarial attacks.

Current designs in distributed systems rely on message-passing based protocols and come at a huge energy and bandwidth cost along with high system complexity. In contrast, our designed systems based on QoT support new temporal use cases of globally distributed applications with low computation and communication overhead. We released our system designs to support various time management and clock synchronization use cases in emerging distributed applications.

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