04_1 - High-Reliability Architectures for Networks under...

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High-Reliability Architectures for Networks under Stress Guy E. Weichenberg, Vincent W. S. Chan, Muriel M´edard Laboratory for Information and Decision Systems Massachusetts Institute of Technology Abstract — In this paper, we consider the design of a physical network topology that meets a high level of reliability using un- reliable network elements. We are motivated by the use of net- works, and in particular, all-optical networks, for high-reliability applications which involve unusual and catastrophic stresses. Our network model is one in which nodes are invulnerable and links are subject to failure, and we consider both statistically indepen- dent and dependent link failures. Our reliability metrics are the all-terminal connectedness measure and the less commonly con- sidered two-terminal connectedness measure. We compare in the low and high stress regimes, via analytical approximations and simulations, common commercial architectures designed for all- terminal reliability when links are very reliable with alternative architectures which are mindful of both of our reliability metrics and regimes of stress. Furthermore, we show that for independent link failures network design should be optimized with respect to reliability under high stress, as reliability under low stress is less sensitive to graph structure; and that under high stress, very high node degrees are required to achieve moderate reliability perfor- mance. Finally, in our discussion of correlated failure models we show the danger in relying on an independent failure model and the need for the network architect to minimize component failure dependencies. Index Terms —system design, graph theory. I. INTRODUCTION AND MOTIVATION Local-area network (LAN) design for applications which de- mand very high levels of reliability is becoming an important research issue owing to the increase in the number of such ap- plications and the inability of commercial architectures to meet their stringent reliability requirements. For example, the transport of control signals in aircraft re- quires virtually uninterrupted communication in the face of a variety of stresses (see Figure 1). Commercial architectures are unable to provide this level of service, as they are typi- cally designed to recover from single failures at a given time with unacceptable delays on the order of tens of milliseconds. High-reliability applications inherently require rich connected- ness among network nodes to provide multiple communication paths, in addition to specially designed protocols to ensure that temporal disruptions in communication are mitigated as much as possible. In this work, we focus on the former requirement of rich connectedness among network nodes. The cost of rich connectedness is a secondary issue in LANs in contrast to wide- area networks (WANs), where connectedness is hampered by The research in this paper was supported by: Defense Advanced Research Projects Agency, “Robust Architectures for Multi-Service, Multi-Level Reli-
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04_1 - High-Reliability Architectures for Networks under...

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