一种抵抗搭便车行为的概率式连接交换unchoking策略

BitTorrent文件共享系统中的搭便车(free-riding)节点会使系统性能大幅下降,目前,BitTorrent主要采用choking策略来抑制搭便车行为,但与choking合作而存在的随机选择节点的unchoking策略仍然给搭便车行为提供了机会.提出了一种基于概率连接交换(probabilistic link exchange,简称PLX)的unchoking策略,在实现unchoking功能的同时,有效地抑制了搭便车行为.由于搭便车节点不提供上传,所以choking以后没有指向搭便车节点的连接,此时, PLX的连接交换机制就能抑制搭便车节点进入文件共享系统.另外,通过对连接交换概率的数学控制,PLX可以区分节点对共享系统的贡献,并根据贡献大小调整其在共享网络中的位置,进一步保证了公平性.最后,对PLX的影响进行了深入的理论分析和模拟实验验证,结果表明:PLX unchoking策略较现有的抵抗搭便车的方法更简单、直接,在效果上有明显提升.

Unchoking Scheme Based on Probabilistic Link Exchange to Resist Free-Riding

Free-riding destroy the foundation of BitTorrent file sharing, and result in bad system performance. The choking scheme adopted in BitTorrent nowadays can suppress the free-riding, however the coexisting unchoking scheme in which the random peers are chosen lend opportunities to free-riders. An unchoking scheme based on probabilistic link exchange, or PLX for short, is provided in this paper. The new scheme can suppress the free-riding effectively while guaranteeing the unchoking function. Free-riders can't enter into the system because they will not be unchoked by PLX after the links to free-riders are choked as PLX works based on link exchanges. Furthermore, by virtue of the mathematical designs for the probability of the link exchange, PLX can distinguish the contribution of peers, adjust their location in network according to contribution, and improve the fairness of the system. The in-depth theoretical analyses and experimental evaluations show that comparing with other methods for fighting against free-riding attacks, the PLX unchoking scheme is simple, direct and effective..