D hot net selectively rewired pa net e hot net started

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Unformatted text preview: k speed with limited connectivity (longhaul connectivity) • Edge routers (access routers) – support wide range of low-speed connections (this traffic then aggregated and sent on to core) also wide range of technologies (dial-up, DSL, cable, etc) with wide range of pricing strategies. “Heuristically Optimal Topologies” • Core routers – high bandwidth, low connectivity • Edge routers – Many low bandwidth connections, aggregating traffic as close to edge as possible. (d) HOT net (selectively rewired PA net), (e) HOT net started from core observed in real-world provider (Abilene), replacing non-Abilene nodes. Metrics (no clear connection to validation) • Performance: maximum throughput of graph g , under gravity model of traffic. • Likelihood: S (g ) = s(g ) smax , where s(g ) = edges wiwj . – degree-degree correlations – s(g) similar to assortativity/dissortativity in ways. High s(g) means hubs connected together and will form core. Empirical data, I • Abilene network (Internet backbone for higher education use, carries 1% of traffic in North America). • CENIC (California education network) “Validation” (a) (b) • (a) Qualitative agreement with HOT derived network • (b) Observed routers sort of seem to segregate into core/edge of their first principles. Empirical data, II (a) (b) • (a) Anonymized ISP, (b) Rocketfuel sampled. • “the point here is that even a heuristic process informed by a detailed understanding of router role and technology constraints can go a long way toward generating realistic annotated router-level maps. While not conclusive, what is remarkable about these results is that the simple assumptions for (fixed) link bandwidths in Table I result in bandwidthdegree combinations that are not inconsistent with our understanding of heuristically optimal network design.” Further points • High variability could be due exclusively to edge. Variability in link technologies (DSL, dial-up, cable) and user demands (pricing). • High variability may be due to errors in sampling approaches (e.g., traceroute) • “Achilles’ Heel” – hubs in core make networks vulnerable to targeted attack. – hubs in periphery have little impact on connectivity. – HOT networks more robust, even “damaged” HOT net better than intact PA network. Comments • Lacks objectivity (heavy self-citation) • Matching the constraint-capacity performance curve does not validate that their first principles approach produces a true topology. • Specific to internet topology (which is their point) / first principles. • See also: W. Willinger, D. Alderson, and J.C. Doyle. “Mathematics and the Internet: A source of enormous confusion and great potential”, Notices of the American Mathematical Society, 56(5):286-299, May 2009. Model Validation Lit Review: Conclusions • New techniques being introduced (classifiers, PCA). • Calls for necessity of validation (e.g., Mitzenmacher) • Specifics may matter, constraint curves “first principles”. • Selection easier than validation!...
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This document was uploaded on 03/12/2014 for the course CSCI 289 at UC Davis.

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