Carlo Marchetti Roberto Baldoni Sara Tucci Piergiovanni Antonino Virgillito Fully Distributed Three-Tier Active Software Replication. 633-645 2006 17 IEEE Trans. Parallel Distrib. Syst. 7 http://doi.ieeecomputersociety.org/10.1109/TPDS.2006.89 db/journals/tpds/tpds17.html#MarchettiBTV06