Epidemic broadcast trees

There is an inherent trade-off between epidemic and deterministic tree-based broadcast primitives. Tree-based approaches have a small message complexity in steady-state but are very fragile in the presence of faults. Gossip, or epidemic, protocols have a higher message complexity but also offer much higher resilience. This paper proposes an integrated broadcast scheme that combines both approaches. We use a low cost scheme to build and maintain broadcast trees embedded on a gossip-based overlay. The protocol sends the message payload preferably via tree branches but uses the remaining links of the gossip overlay for fast recovery and expedite tree healing. Experimental evaluation presented in the paper shows that our new strategy has a low overhead and that is able to support large number of faults while maintaining a high reliability.This work was partially supported by project P-SON: Probabilistically Structured Overlay Networks (POSC/EIA/60941/2004)

Field Tests of Kairomones to Increase Parasitism of Spruce Budworm (Lepidoptera: Tortricidae) Eggs by \u3ci\u3eTrichogramma\u3c/i\u3e Spp. (Hymenoptera: Trichogrammatidae)

Hexane extracts of spruce budworm, Choristoneura fumiferana, moth scales, applied at 0.04 moth-gram equivalents/branch and at 0.06 moth-gram equivalents/tree, failed to increase parasitism rates of Trichogramma spp. in two cutover spruce-fir stands in Maine. Releasing Maine-strain T. minutum apparently increased parasitism rates about 20-fold. However, application of kairomone extracts to whole branches and to upper crowns of small trees may have interfered with host-searching behaviors of Trichogramma parasitoids

Broadcasting in Prefix Space: P2P Data Dissemination with Predictable Performance

A broadcast mode may augment peer-to-peer overlay networks with an efficient, scalable data replication function, but may also give rise to a virtual link layer in VPN-type solutions. We introduce a simple broadcasting mechanism that operates in the prefix space of distributed hash tables without signaling. This paper concentrates on the performance analysis of the prefix flooding scheme. Starting from simple models of recursive $k$-ary trees, we analytically derive distributions of hop counts and the replication load. Extensive simulation results are presented further on, based on an implementation within the OverSim framework. Comparisons are drawn to Scribe, taken as a general reference model for group communication according to the shared, rendezvous-point-centered distribution paradigm. The prefix flooding scheme thereby confirmed its widely predictable performance and consistently outperformed Scribe in all metrics. Reverse path selection in overlays is identified as a major cause of performance degradation.Comment: final version for ICIW'0

Epidemic Thresholds with External Agents

We study the effect of external infection sources on phase transitions in epidemic processes. In particular, we consider an epidemic spreading on a network via the SIS/SIR dynamics, which in addition is aided by external agents - sources unconstrained by the graph, but possessing a limited infection rate or virulence. Such a model captures many existing models of externally aided epidemics, and finds use in many settings - epidemiology, marketing and advertising, network robustness, etc. We provide a detailed characterization of the impact of external agents on epidemic thresholds. In particular, for the SIS model, we show that any external infection strategy with constant virulence either fails to significantly affect the lifetime of an epidemic, or at best, sustains the epidemic for a lifetime which is polynomial in the number of nodes. On the other hand, a random external-infection strategy, with rate increasing linearly in the number of infected nodes, succeeds under some conditions to sustain an exponential epidemic lifetime. We obtain similar sharp thresholds for the SIR model, and discuss the relevance of our results in a variety of settings.Comment: 12 pages, 2 figures (to appear in INFOCOM 2014