Scheduling Distributed Real-Time Tasks in Unreliable and Untrustworthy Systems
In this dissertation, we consider scheduling distributed soft real-time tasks in unreliable (e.g., those with arbitrary node and network failures) and untrustworthy systems (e.g., those with Byzantine node behaviors). We present a distributed real-time scheduling algorithm called Gamma. Gamma consid...
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Format: | Others |
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Virginia Tech
2014
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Online Access: | http://hdl.handle.net/10919/26917 http://scholar.lib.vt.edu/theses/available/etd-04162010-132432/ |
Summary: | In this dissertation, we consider scheduling distributed soft real-time tasks in unreliable
(e.g., those with arbitrary node and network failures) and untrustworthy systems (e.g., those
with Byzantine node behaviors). We present a distributed real-time scheduling algorithm
called Gamma. Gamma considers a distributed (i.e., multi-node) task model where tasks are
subject to Time/Utility Function (or TUF) end-to-end time constraints, and the scheduling
optimality criterion of maximizing the total accrued utility. The algorithm makes three novel
contributions. First, Gamma uses gossip for reliably propagating task scheduling parameters
and for discovering task execution nodes. Second, Gamma achieves distributed real-time
mutual exclusion in unreliable environments. Third, the algorithm guards against potential
disruption of message propagation due to Byzantine attacks using a mechanism called
Launcher-Attacker-Infective-Susceptible-Immunized-Removed-Consumer (or LAISIRC). By
doing so, the algorithm schedules tasks with probabilistic termination-time satisfactions,
despite system unreliability and untrustworthiness.
We analytically establish several timeliness and non-timeliness properties of the algorithm
including probabilistic end-to-end task termination time satisfactions, optimality
of message overheads, mutual exclusion guarantees, and the mathematical model of the
LAISIRC mechanism. We conducted simulation-based experimental studies and compared
Gamma with its competitors. Our experimental studies reveal that Gammaâ s scheduling algorithm
accrues greater utility and satisfies a greater number of deadlines than do competitor
algorithms (e.g., HVDF) by as much as 47% and 45%, respectively. LAISIRC is more tolerant
to Byzantine attacks than competitor protocols (e.g., Path Verification) by obtaining as much as 28% higher correctness ratio. Gammaâ s mutual exclusion algorithm accrues greater
utility than do competitor algorithms (e.g., EDF-Sigma) by as much as 25%. Further, we
implemented the basic Gamma algorithm in the Emulab/ChronOS 250-node testbed, and
measured the algorithmâ s performance. Our implementation measurements validate our
theoretical analysis and the algorithm's effectiveness and robustness. === Ph. D. |
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