P2P网络的核心机制ppt课件.pptVIP

P2P网络的核心机制 章节内容 4.1 覆盖网拓扑结构 4.2 分布式散列表 4.3 路由和定位 4.4 查询和有哪些信誉好的足球投注网站 4.5 动态结点算法 4.6 容错性 4.1 覆盖网拓扑结构 P2P网络是构建在底层物理网（如IP网）上的应用层覆盖网，拓扑结构对P2P网络的工作性能以及设计机制有决定性作用 典型拓扑结构：带弦环、树、Plaxton Mesh、环面、超立方体、蝴蝶、异或 问题：拓扑结构对P2P性能的影响情况？ Geometries Nature FNS FRS Performance Resilience Latency Geometries considered Geometry = Flexibility = Performance Geometry captures flexibility in selecting algorithms Flexibility is important for routing performance Flexibility in selecting routes leads to shorter, reliable paths Flexibility in selecting neighbors leads to shorter paths Metrics for flexibility FNS: Flexibility in Neighbor Selection = number of node choices for a neighbor FRS: Flexibility in Route Selection = avg. number of next-hop choices for all destinations Constraints for neighbors and routes select neighbors to have paths of O(logN) select routes so that each hop is closer to destination Summary of flexibility analysis Static Resilience Two aspects of robust routing Dynamic Recovery : how quickly routing state is recovered after failures Static Resilience : how well the network routes before recovery finishes captures how quickly recovery algorithms need to work depends on FRS Evaluation: Fail a fraction of nodes, without recovering any state Metric: % Paths Failed Does flexibility affect Static Resilience? Geometry’s impact on Proximity Both FNS and FRS can reduce latency Tree has FNS, Hypercube has FRS, Ring XOR have both Metric: Overlay Path Latency Which is more useful: FNS or FRS? Plain FRS FNS ≈ FNS+FRS Neighbor Selection is much better than Route Selection 小结 拓扑结构影响性能，其中FRS对resilence显著，而FNS对latency显著。设计需要tradeoff 参考论文： [Gummadi et al.03] K. P. Gummadi, R. Gummadi, S. D. Gribble, S. Ratnasamy, S. Shenker and I. Stoica. The Impact of DHT Routing Geometry on Resilience and Proximity. In SIGCOMM 2003, pp. 381-394. 4.2 分布式散列表 分布式散列表(DHT，Distributed hash table)是P2P网络的核心设施，它基于一致性散列函数，提供对于结点、数据对象在覆盖网中的位置映射 结点的映射可以保证准确的定位，还提供了匿名性 数据对象映射的作用在于将其索引信息放到nodelD与objectID最