The Delta-4 extra performance architecture (XPA)

As part of the European Strategic Programme for Research in Information Technology (ESPRIT), the Delta4 project is seeking to define an open, fault-tolerant, distributed computing architccturc. The Delta-4 approach to fault-tolerance is based upon the replication of software components on distinct host computers using a range of different replication strategies. teraction faults (intrusions) and software design faults is also being addressed. Extensive validation activities are being car&d out to justify the reliance being placed on the architecture. This paper presents the design of an Extra Performance Architecture for Delta-4 which explicitly supports the requirements of real-time systems with respect to throughput and response. The problems of replicate divergence are discussed, and a solution based on message selection and preemption synchronisation messages is proposed. The paper includes a description of the on-going implementation of such a system within the overall Delta-4 framework. Openness. in the context of the project, has a number of implications. Firstly, the Delta-4 architecture must be capable of co-existing with. and inter-working under, standards conforming to the Open Systems Interconnection (OSI) reference model. Delta-4 will accommodate existing proprietary computer systems, and the connection of heterogeneous equipment via one or more inter-connected local area networks. Secondly, the Delta-4 Application Support Euvironrnent (Deltase) will conform to the emerging standard for a Support Environment for Open Distributed Processing (SE-ODP) proposed by the European Computer Manufacturers Association (ECMA) working group TC32/IG2. Finally, the results of the project are publish&