A quality of service based framework for dynamic, dependable systems

There is currently much UK government and industry interest towards the integration of complex computer-based systems, including those in the military domain. These systems can include both mission critical and safety critical applications, and therefore require the dependable communication of data. Current modular military systems requiring such performance guarantees are mostly based on parameters and system states fixed during design time, thus allowing a predictable estimate of performance. These systems can exhibit a limited degree of reconfiguration, but this is typically within the constraints of a predefined set of configurations. The ability to reconfigure systems more dynamically, could lead to further increased flexibility and adaptability, resulting in the better use of existing assets. Current software architecture models that are capable of providing this flexibility, however, tend to lack support for dependable performance. This thesis explores the benefits for the dependability of future dynamic systems, built on a publish/subscribe model, from using Quality of Service (QoS) methods to map application level data communication requirements to available network resources. Through this, original contributions to knowledge are created, including; the proposal of a QoS framework that specifies a way of defining flexible levels of QoS characteristics and their use in the negotiation of network resources, a simulation based evaluation of the QoS framework and specifically the choice of negotiation algorithm used, and a test-bed based feasibility study. Simulation experimentation conducted comparing different methods of QoS negotiation gives a clear indication that the use of the proposed QoS framework and flexible negotiation algorithm can provide a benefit in terms of system utility, resource utilisation, and system stability. The choice of negotiation algorithm has a particularly strong impact on these system properties. The cost of these benefits comes in terms of the processing power and execution time required to reach a decision on the acceptance of a subscriber. It is suggested, given this cost, that when computational resources are limited, a simpler priority based negotiation algorithm should be used. Where system resources are more abundant, however, the flexible negotiation algorithm proposed within the QoS framework can offer further benefits. Through the implementation of the QoS framework within an existing military avionics software architecture based emulator on a test-bed, both the technical challenges that will need to be overcome and, more importantly, the potential viability for the inclusion of the QoS framework have been demonstrated

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

A quality of service framework for adaptive and dependable large scale system-of-systems

There is growing recognition within industry that for system growth to be sustainable, the way in which existing assets are used must be improved. Future systems are being developed with a desire for dynamic behaviour and a requirement for dependability at mission critical and safety critical levels. 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 is based around a publish/subscribe model, an approach that, while adaptive, does not typically support critical levels of performance. There is, however, the scope 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. A QoS based framework is proposed for providing adaptive and dependable behaviour for future large-scale system-of-systems. Initial simulation results are presented to demonstrate the benefits of QoS

Adaptive architectures for future highly dependable, real time systems

Many present-day safety-critical or mission-critical military applications are deployed using intrinsically static architectures. Often these applications are real-time systems, where late responses may cause potentially catastrophic results. Static architectures allow system developers to certify with a high degree of confidence that their systems will provide correct functionality during operation, but a more adaptive approach could provide some clear benefits. In particular, the ability to dynamically reconfigure the system at run time would give increased flexibility and performance in response to unpredictable or unplanned operating scenarios. Many current dynamic architectural approaches provide little or no features to facilitate the highly dependable, real-time performance required by critical systems. The challenge is to provide the features and benefits of dynamic architectural approaches while still achieving the required level of performance and dependability. This paper describes the early results of an ongoing research programme, part funded by the Software Systems Engineering Initiative (SSEI), aimed at developing a more adaptive software architecture for future military systems. A range of architectures with adaptive features (including object-based, agent based and publish/subscribe) are reviewed against the desirable characteristics of highly dependable systems. A publish/subscribe architecture is proposed as a potential way forward and a discussion of its advantages and disadvantages for highly dependable, real-time systems is given

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

A quality of service framework for adaptive and dependable large scale system-of-systems

There is growing recognition within industry that for system growth to be sustainable, the way in which existing assets are used must be improved. Future systems are being developed with a desire for dynamic behaviour and a requirement for dependability at mission critical and safety critical levels. 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 is based around a publish/subscribe model, an approach that, while adaptive, does not typically support critical levels of performance. There is, however, the scope 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. A QoS based framework is proposed for providing adaptive and dependable behaviour for future large-scale system-of-systems. Initial simulation results are presented to demonstrate the benefits of QoS