Client-access protocols for replicated services

This paper addresses the problem of replicated service provision in distributed systems. Existing systems that follow the State Machine approach concentrate on the synchronization of the server replicas and do not consider the problem of client interaction with the server group. The paper analyzes client interaction and identifies a number of access protocols to meet a range of client requirements and system models. The paper demonstrates that protocols for the "open" group model-clients external to the group of servers-satisfy the requirements of the State Machine approach, even when replication is transparent to the clients. Experimental performance results indicate that the "open" model is clearly desirable when the service is used by a large, dynamically changing set of clients. The situation which pertains to Internet service provision.