A troupe is a set of replicas of a module, executing on machines that have independent failure modes. Troupes are the building blocks of replicated distributed programs and the key to achieving high availability. Individual members of a troupe do not communicate among themselves, and axe unaware of one another's existence; this property is what distinguishes troupes from other software architectures for fault tolerance.Replicated procedure call is introduced to handle the many-to-many pattern of conmmnication between troupes. The semantics of replicated procedure call can be summarized as exactly-once execution at all replicas.An implementation of troupes and replicated procedure call is described, and its performance is measured. The problem of concurrency control for troupes is examined, and a commit protocol for replicated atomic transactions is presented. Binding and reconfiguration mechanisms for replicated distributed programs are described.otherwise, or to republish, requires a fee and/or specific permission. © 1985ACM-0-89791-174-1-12/85-0063 $00.75 this approach was proposed by yon Neumann thirty years ago [29]. The idea is to replicate each component to such a degree that the probability of all replicas failing becomes acceptably small. The advent of inexpensive distributed computing systems (consisting of computers connected together by a network) makes replication an attractive and practical means of tolerating hardware crashes.

is in the soware group at Fore Systems, where his responsibilities include the switch control sofiare described in this article. ERIC COOPER cofounded Fore Systems to commercialize ATM LANs. As president and CEO, he has overall responsibility forATMtechnohgv at Fore Systems. ROBERT SANSOM is cofounder and executive vice president of Fore Systems, Inc. He manages Fore Systems' business development and is responsible for Fore Systems' technical stmtegv.

Wc have built a high-speed local-area network called Nectar that uses programmable communication processors as host interfaces. In contrast to most protocol engines, our communication processors have a flexible runtime system that supports multiple transport protocols as well as application-specific activities. In particular, we have implemented the TCP/IP protocol suite and Nectar-specific communication protocols on the communication processor. The Nectar network currently has 25 hosts and has been in use for over a year. The flexibility of our communication processor design does not compromise its performance. The latency of a remote procedure call between application tasks executing on two Nectar hosts is less than 500 //sec. The same tasks can obtain a throughput of 28 Mbit/sec using either TCP/IP or Nectar-specific transport protocols. This throughput is limited by the VME bus that connects a host and its communication processor. Application tasks executing on two communication processors can obtain 90 Mbit/sec of the possible 100 Mbit/sec physical bandwidth using Nectar-specific transport protocols.PITTSBURGH, PA 15213-3SSP

A troupe is a set of replicas of a module, executing on machines that have independent failure modes. Troupes are the building blocks of replicated distributed programs and the key to achieving high availability. Individual members of a troupe do not communicate among themselves, and axe unaware of one another's existence; this property is what distinguishes troupes from other software architectures for fault tolerance.Replicated procedure call is introduced to handle the many-to-many pattern of conmmnication between troupes. The semantics of replicated procedure call can be summarized as exactly-once execution at all replicas.An implementation of troupes and replicated procedure call is described, and its performance is measured. The problem of concurrency control for troupes is examined, and a commit protocol for replicated atomic transactions is presented. Binding and reconfiguration mechanisms for replicated distributed programs are described.