Hakim Weatherspoon John Kubiatowicz Efficient heartbeats and repair of softstate in decentralized object location and routing systems. 182-185 2002 ACM SIGOPS European Workshop http://doi.acm.org/10.1145/1133373.1133409 conf/sigopsE/2002 db/conf/sigopsE/sigopsE2002.html#WeatherspoonK02