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The PSTR/SNS Scheme for Real-Time Fault Tolerance via Active Object Replication and Network Surveillance

The TMO (Time-triggered Message-triggered Object) scheme was formulated as a major extension of the conventional object structuring schemes with the idealistic goal of facilitating general-form design and timeliness-guaranteed design of complex real-time application systems. Recently, as a new scheme for realizing TMO-structured distributed and parallel computer systems that are capable of both hardware and software fault tolerance, we have formulated and demonstrated the PSTR (Primary-Shadow TMO Replication) scheme. An important new extension of the PSTR scheme discussed in this paper is an integration of the PSTR scheme and a network surveillance (NS) scheme. This extension results in a significant improvement in the fault coverage and recovery time bound achieved. The NS scheme adopted is a recently-developed scheme that is effective in a wide range of point-to-point networks, and it is called the SNS (Supervisor-based Network Surveillance) scheme. The integration of the PSTR scheme and the SNS scheme is called the PSTR/SNS scheme. The recovery time bound of the PSTR/SNS scheme is analyzed on the basis of an implementation model that can be easily adapted to various commercial operating system kernels.