Quality of service (QoS) has been receiving wide attention in recent years in many research communities including networking, multimedia systems, real-time systems and distributed systems. In large distributed systems such as those used in defense systems, on-demand service and inter-networked systems, applications contending for system resources must satisfy timing, reliability and security constraints as well as application-specific quality requirements. Allocating sufficient resources to different applications in order to satisfy various requirements is a fundamental problem in these situations. A basic yet flexible model for performance-driven resourceallocations can thereforebe useful in making appropriate tradeoffs. In this paper, we present an analytical model for QoS management in systems which must satisfy application needs along multiple dimensions such as timeliness, reliable delivery schemes, cryptographic security and data quality. We refer to this model as Q-RAM (QoS-based Res...

RAM) proposed in [20] presented an analytical approach for satisfying multiple quality-of-service dimensions in a resource-constrained environment. Using this model, available system resources can be apportioned across multiple applications such that the net utility that accrues to the end-users of those applications is maximized. In this paper, we present several practical solutions to allocation problems that were beyond the limited scope of [20]. First, we show that the Q-RAM problem of finding the optimal resource allocation to satisfy multiple QoS dimensions (at least one of which is dependent on another) is NP-hard. We then present a polynomial solution for this resource allocation problem which yields a solution within a provably fixed and short distance from the optimal allocation. Secondly, [20] dealt mainly with the problem of apportioning a single resource to satisfy multiple QoS dimensions. In this paper, we study the converse problem of apportioning multiple resources to satisfy a single QoS dimension. In practice, this problem becomes complicated, since a single QoS dimension perceived by the user can be satisfied using different combinations of available resources. We show that this problem can be formulated as a mixed integer programming problem that can be solved efficiently to yield an optimal resource allocation. Finally, we also present the run-times of these optimizations to illustrate how these solutions can be applied in practice. We expect that a good understanding of these solutions will yield insights into the general problem of apportioning multiple resources to satisfy simultaneously multiple QoS dimensions of multiple concurrent applications. 1.

Introduction Recent research on imprecise computation (that is, flexible computation) at the University of Illinois has focused on the development of operating system support for imprecise computations. The scheduling algorithms and imprecise-computation environment resulting from this work enable the use of imprecise computation as a means to provide scheduling flexibility in real-time systems and to enhance their fault tolerance and allow graceful degradation [7, 9]. A real-time system is one in which tasks have deadlines. A hard realtime system fails if any task does not produce its result by its deadline. Here, the term task loosely refers to a unit of work that is executed by the system to provide some service. FFT and multiple target tracking computations are examples of tasks, as are multimedia transmissions, displays, and operator actions. It is possible to design many real-time applications so that thei

Simulation is often used in the analysis of complex computing systems. The design and validation of complex real-time systems demands capabilities not found in existing simulation environments. We categorize these capabilities into three major functional areas: search control, the execution engine, and output analysis. Search control is an imporant topic often treated lightly in simulation environments for real-time systems. The search controller chooses values for variable input parameters and launches simulation sto determine the performance of the system under different sets of parameter values. The search control framework presented in this thesis allows both conventional design and search and also validation search

Current distributed multimedia applications demand Quality of Service from the system to facilitate effective services to the end users. However, within the range of QoS demands appropriately specified by the application, lower level transport facilities may not be able to constantly provide Quality of Service without perturbations. We introduce facilities in the middleware level to perform Quality of Service adaptations on a specific Quality of Service metric that is measured from the raw Quality of Service provided by the underlying layers, and refer to the component performing the task as adaptors. We are able to approach Quality of Service adaptations from a different perspective with a simplified but precise model for Quality of Service metrics, adaptations, and the adaptation behavior. Utilizing theories and techniques from the digital control theories and digital signal processing, we are able to model adaptation stability and agility of the performed adaptation behavior, and to introduce methods to analyze and configure the transformations according to the demands specified by the distributed multimedia applications. iii TO MY PARENTS iv Acknowledgments First and foremost, I would like to thank my thesis advisor, Professor Klara Nahrstedt, for her invaluable directions and support throughout my research efforts towards this thesis. Her insights and suggestions to the problems presented in this thesis enlightened me in various detailed aspects through the work. I would also like to acknowledge the constant assistance and encouragements from my best friends. Among them, special thanks goes to Dongyan Xu, who was also conducting research in the area of Quality of Service, and who has been generously taking time to discuss research possibilities with me, as well...

In this work, we present a hybrid control structure for a mobile robotic system which combines concepts from homeostatic control and adaptive behavior. The homeostatic control consists of a set of control loops operating on state variables. These variables are computed from pre-categorical sensory data and also from high-level application results. The adaptive behavior is implemented by a fuzzy controller whose rules dynamically modify several system parameters, using the same structure to control both low-level homeostatic loops and high-level application tasks. The objective of this proposal is twofold: guarantee an acceptable image quality keeping the perceptual data into a homeostatic regime, and use the adaptive behavior to obtain a better resource management and dynamic response. To validate this proposal we have carried out some experiments using a mobile robot which performs a line following task under variable lighting conditions. 1

Abstract—In this paper, an exception-based programming paradigm is envisioned to deal with timing constraints violations occurring in soft real-time and multimedia applications written in the C language. In order to prove viability of the approach, a mechanism allowing to use such paradigm has been designed and implemented as an open-source library of C macros making use of the standard POSIX API (a few Linux-specific optimizations are also briefly discussed). The envisioned approach has been validated by modifying mplayer, one of the most widely used multimedia player for Linux, so as to use the introduced library. Experimental results demonstrate how the exception-based paradigm is effective in improving the audio/video delay exhibited by the player. I.

The problem of over-running in hard real-time systems poses critical risks to the hardware under control. The imprecise computation technique offers an effective way of resource utilization in these cases. We introduce Imprecise-DEVS (I-DEVS), a model-driven approach to develop real-time and embedded applications based on the DEVS (Discrete Event Systems Specification) formalism. This approach combines the dynamic advantages of the imprecise computation technique with the rigor of a formal modeling methodology. This framework can be used to develop embedded applications incrementally, integrating imprecise models with hardware components seamlessly. We have defined structural modifications to DEVS in order to allow imprecise model definition. 1.