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Eighth IEEE International Symposium on Object-Oriented Real-Time Distributed Computing (ISORC'05) (2005)
Seattle, Washington
May 18, 2005 to May 20, 2005
ISBN: 0-7695-2356-0
pp: 267-274
Paul Ezhilchelvan , University of Newcastle, UK
Jean-Michel H?lary , IRISA, France
Michel Raynal , IRISA, France
This paper is on the construction of a fault-tolerant and responsive server subsystem in an application context where the subsystem is accessed through an asynchronous network by a large number of clients. The server is made fault-tolerant by the Triple Modular Redundancy (TMR) technique: at least two server processes behave correctly, while the third one can behave arbitrarily. An essential requirement for process replication is that the client inputs be delivered to server replicas for processing in an identical order. Moreover, in order to cope with process' memory requirement, a time bound constraint is imposed: no client input can stay in the local memory of a server process more than Σ units of time. Based on known technologies, two assumptions are made: (1) the network delivers a given client input to any two server processes within a known bounded time (D), and (2), there is an Ordered Timed Atomic Broadcast protocol built on top of the TMR system with timeliness Δ. The paper presents two results. The first is a protocol that delivers an ordered stream of client inputs, such that every client input is delivered exactly once to each correct server, thus eliminating redundant verification. It works under the assumption Σ > D + Δ. The second is an impossibility result, namely there can be no ordering protocol where Σ > D + ⍙, where Δ is the minimum timeliness of any reliable broadcast protocol that can be implemented on top of the TMR server (⍙ ≤ Δ).

J. H?lary, M. Raynal and P. Ezhilchelvan, "Building Responsive TMR-Based Servers in Presence of Timing Constraints," Eighth IEEE International Symposium on Object-Oriented Real-Time Distributed Computing (ISORC'05)(ISORC), Seattle, Washington, 2005, pp. 267-274.
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