Service replication is a key to providing high availability, fault tolerance, and good performance in distributed systems. Various replication schemes have been proposed, they are based on two streams of techniques, namely passive replication and active replication. This paper focuses on two implementation approaches of the passive primary-backup scheme, the remote method invocation approach and the replica-proxy approach, using Java RMI and Java network packages respectively. Issues addressed in this paper also include: the primary-backup protocol; restarting a failed server at any site; and a general naming service for the maintenance of dynamic memberships of replica groups. Finally, performance studies based on two implementation approaches are given.