A quality of service framework for dependability in large-scale distributed systems

As recognition grows within industry for the advantages that can be gained through the exploitation of large-scale dynamic systems, a need emerges for dependable performance. Future systems are being developed with a requirement to support mission critical and safety critical applications. These levels of criticality require predictable performance and as such have traditionally not been associated with adaptive systems. The software architecture proposed for such systems takes its properties from the service-oriented computing paradigm and the communication model follows a publish/subscribe approach. While adaptive, such architectures do not, however, typically support real-time levels of performance. There is scope, however, for dependability within such architectures through the use of Quality of Service (QoS) methods. QoS is used in systems where the distribution of resources cannot be decided at design time. In this paper a QoS based framework is proposed for providing adaptive and dependable behaviour for future large-scale dynamic systems through the flexible allocation of resources. Simulation results are presented to demonstrate the benefits of the QoS framework and the tradeoffs that occur between negotiation algorithms of varying complexities.