This paper makes two contributions to the study of configuring real-time aspects into quality of service (QoS)-enabled component middleware and distributed real-time and embedded (DRE) systems. First, it compares and contrasts the integration of real-time aspects into DRE systems using conventional QoS-enabled distributed object computing (DOC) middleware versus QoS-enabled component middleware. Second, it presents experiments that evaluate several real-time aspects con gured in The ACE ORB (TAO) versus in the Component-Integrated ACE ORB (CIAO). Our results show that QoS-enabled component middleware implementations can offer real-time performance that is comparable to DOC middleware, while offering greater flexibility in composing and configuring key DRE system aspects.

Avionics mission computing systems have traditionally been scheduled statically. Static scheduling provides assurance of schedulability prior to run-time and can be implemented with low runtime overhead. However, static scheduling handles non-periodic processing inefficiently, and treats invocation-to-invocation variations in resource requirements inflexibly. As a consequence, processing resources are underutilized and the resulting systems are hard to adapt to meet worst-case processing requirements. Dynamic scheduling has the potential to offer relief from some of the restrictions imposed by strict static scheduling approaches. Potential benefits of dynamic scheduling include better tolerance for variations in activities, more flexible prioritization, and better CPU utilization in the presence of non-periodic activities. However, the cost of these benefits is expected to be higher run-time scheduling overhead and additional application development complexity. This report reviews the...

Distributed object computing forms the basis for nextgeneration application middleware. At the heart of distributed object computing are Object Request Brokers (ORBs), which automate many tedious and error-prone distributed programming tasks. Like many other distributed applications, conventional ORBs use statically configured software designs, which are hard to maintain, port, and optimize. Likewise, conventional ORBs cannot be extended without modifying their source code, which forces recompilation, relinking, and restarting running ORBs and their associated application objects. This article makes two contributions to the study of extensible and maintainable ORB middleware. First, it presents a case study of key design patterns needed to develop ORBs that can be dynamically configured and evolved for specific application requirements and system characteristics. Second, we quantify the impact of applying patterns to reduce the complexity and improve the maintainability of common ORB tasks.

Distributed object computing forms the basis of nextgeneration communication software. At the heart of distributed object computing are Object Request Brokers (ORBs), which automate many tedious and error-prone distributed programming tasks. Like much communication software, conventional ORBs use statically configured designs, which are hard to port, optimize, and evolve. Likewise, conventional ORBs cannot be extended without modifying their source code, which forces recompilation, relinking, and restarting running ORBs and their associated application objects. This paper makes two contributions to the study of extensible ORB middleware. First, it presents a case study illustrating how a pattern language can be used to develop dynamically configurable ORBs that can be customized for specific application requirements and system characteristics. Second, we quantify the impact of applying this pattern language to reduce the complexity and improve the maintainability of common ORB tasks, ...

Adaptation of distributed software to maintain the best possible application performance in the face of changes in available resources is an increasingly important and complex problem. We discuss the application of the QuO adaptive middleware framework and the CORBA A/V Streaming Service to the development of real-time embedded applications. We demonstrate a standards-based middleware platform for developing adaptive applications that are better architected and easier to modify and that can adapt to changes in resource availability to meet QoS requirements. These are presented in the context of a video distribution application. The application is developed using QuO and the A/V Streaming Service, and uses adaptive behavior to meet timeliness requirements in the face of restrictions in processing power and network bandwidth. We present experimental results we have gathered for this application. 1.

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Middleware is increasingly used as the infrastructure for applications with stringent quality of service (QoS) requirements, including scalability. One way to improve the scalability of distributed applications is to use adaptive middleware to balance system processing load dynamically among multiple servers.

Next-generation distributed interactive simulations have stringent quality of service (QoS) requirements for throughput, latency, and scalability, as well as requirements for a flexible communication infrastructure to reduce software lifecycle costs. The CORBA Event Service provides a flexible model for asynchronous communication among distributed and collocated objects. However, the standard CORBA Event Service specification lacks important features and QoS optimizations required by distributed interactive simulation systems.

It is widely accepted that in order to deliver the best Quality-of-Service (QoS), applications need to be adaptive to the fluctuating computing and communication environments. The middleware layer may assist such adaptation behavior in two ways. First, the middleware may adapt and reconfigure itself in order to transparently provide a stable and predictable environment to the application. Second, it may control the behavior of the applications so that they adapt and reconfigure themselves. The latter alternative enjoys the advantage of knowing exactly what are the application-specific adaptation priorities and requirements, but lacks an easy way to pinpoint the relationships between applicationspecific adaptation choices and the actual changes in resource demands, caused by reconfiguring an adaptive application. In this paper, we present QualProbes, a set of middleware QoS Probing and Profiling services to discover such relationships at run-time. Our approach focuses on meeting the requirements of the critical performance criterion in the application. Frequently, such criterion may be affected by changes in more than one application-specific QoS parameters, and these parameters have diversely different resource usage patterns. QualProbes services are able to precisely capture the effects made to the critical performance criterion when resource availability varies, and thus enable more effective control of the application to adapt to resource variations. Our case study with OmniTrack, an omni-directional visual tracking application, provides solid proof that QualProbes significantly enhance our capabilities to satisfy the critical performance criterion, the tracking precision, while controlling the adaptation process of the application. QualProbes: Mid...

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