A well accepted technique to ensure reliability in a distributed system is to replicate every object which performs critical processing. However, it is not easy to achieve replication, i.e to enable a replicated object to communicate with other objects, just as if it were not replicated. This paper presents problems raised by replication encapsulation and describes the solution proposed by the N2M service. The latter allows replicated client objects to communicate with replicated server objects using regular invocations. The N2M service defines a symetric invocation model to achieve replication encapsulation.