Software replication in three-tiers architectures: is it a real challange?

This paper is a first attempt to study the problem of handling software replication in three tiers architectures. In particular a study based on synchronization and communication patterns imposed by replication is presented. We show how the complexity of the replication scheme is affected by the deterministic (or not) behavior of the members of the backtier We also give two generic synchronization and communication patterns used in two and three tiers replication. Well-known schemes such us active and passive replication are particular instances of these generic patterns.