W eaddr esstheproblem ofhighly transient populations inunstructur edandloosely-structur edpeer-to-peer systems. Wepropose anumber ofillustrati vequery-r elated strategies and organizational protocols that, bytaking into consideration theexpected session times ofpeers (their lifespans), yield systems with performance characteristics moreresilient tothe natural instability oftheir environments. Wefirst demonstrate thebenefits oflifespan-based organizational protocols interms ofend-application performance and inthecontext ofdynamic and heter ogeneous Inter net environments. Wedothis using anumber ofcurrently adopted and proposed query-r elated strategies, including methods forquery distrib ution, caching and replication. Wethen show,through trace-dri vensimulation and wide-ar eaexperimentation, the performance advantages oflifespan-based, query-r elated strategies when layeredover currently employ edand lifespan-based organizational protocols. While merelyillustrati ve,theevaluated strategies and protocols clearly demonstrate theadvantages ofconsidering peers’ session time indesigning widely-deploy edpeer-to-peer systems. IndexTerms —Lifespan, session time, resilience, peer-to-peer . I.INTRODUCTION Peer-to-peer (P2P) computing canbedefined asthesharing ofcomputer resources and services bydirect exchange between theparticipating nodes. Since Napster’ s[2]introduction inthelate90s, thearea hasrecei vedincreasing attention from theresearch community andthegeneral public. Peers inP2P systems typically define anoverlay netw orktopology bykeepinganumber ofconnections toother peers, their “friends, ” and implementing amaintenance protocol that continuously repairs theoverlay asnewmembers join andothers leavethe system. Due inparttotheautonomous nature ofpeers, their mutual dependenc y,and their astoundingly largepopulations, the transienc yofpeers (a.k.a. churn) and itsimplications on theoverall system’ sperformance haverecently attracted the attention oftheresearch commu