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...

This paper describes the design and operation of a composable proxy infrastructure that enables mobile Internet users to collaborate via heterogeneous devices and network connections. The approach is based on detachable Java I/O streams, which enable proxy filters and transcoders to be dynamically inserted, removed, and reordered on a given data stream. Unlike conventional Java I/O streams, detachable streams can be stopped, disconnected, reconnected, and restarted. As such, they provide a convenient method by which to support the dynamic composition of proxy services. Moreover, use of the I/O stream abstraction enables network distribution and stream adaptability to be implemented transparently with respect to application components. The operation and implementation of detachable streams are described. To evaluate the composable proxy infrastructure, it is used to enhance interactive audio communication among users of a Web-based collaborative computing framework. Two forward error correction (FEC) proxylets are developed, one using block erasure codes and the other using the GSM 06.10 encoding algorithm. Separately, each type of FEC improves the ability of the audio stream to tolerate errors in a wireless LAN environment. When composed in a single proxy, however, they cooperate to correct additional types of burst errors. Results are presented from a performance study conducted on a mobile computing testbed.

In heterogeneous network and operating system environments with a fair amount of performance variations, multiple applications compete and share a limited amount of system resources, and suffer from variations in resource availability. These complex applications, such as OmniTrack, a client-server based omni-directional visual tracking application, are thus desired to adapt themselves and to adjust their resource demands dynamically. Frequently, the ultimate objective of application-level adaptation is to preserve the quality of the most critical application-specific parameter, such as tracking precision, even at the cost of other non-critical parameters such as perceptual quality. On one hand, current adaptation mechanisms built within an application have the disadvantage of lacking global information to preserve fairness among all applications. On the other hand, adaptive resource management mechanisms built within the operating system are not aware of data semantics in the application, and reservation-based resource management mechanisms may need modifications to commodity off-the-shelf operating systems or network protocol stacks widely deployed today. We believe that appropriate application-level QoS adaptation decisions can be achieved with the assistance of a middleware architecture, where both application and system level dynamics can be observed and analyzed to decide when, how and to what extent adaptation has to occur. In this work, we present Agilos (Agile QoS), a novel Middleware Control Architecture to enforce the best possible adaptation decisions for distributed multimedia applications, via dynamic controls and reconfigurations of their internal parameters and functionalities. Several major contributions are presented in this dissertation. First, for mo...

Future-generation distributed multimedia applications are expected to be highly scalable to a wide variety of heterogeneous devices, and highly adaptive across wide-area distributed environments. This demands multiple stages of run-time support in QoS-aware middleware architectures, particularly, probing the performance of QoS parameters, instantiating the initial component configurations, and adapting to on-the-fly variations. However, few of the past experiences in related work has shown comprehensive run-time support in all of the above stages --- they often design and build a middleware framework by focusing on only one of the run-time issues. In this paper, we argue that distributed multimedia applications need e#ective run-time middleware support in all these stages in order to be highly scalable and adaptive across a wide variety of execution environments. Nevertheless, the design of such middleware framework should be kept as streamlined and simple as possible, leading to a novel and integrated run-time middleware platform to unify the probing, instantiation and adaptation stages. In addition, for each stage, the framework should enable the interaction of peer middleware components across host boundaries, so that the corresponding middleware function can be performed in a coordinated and coherent fashion. We present the design of such an integrated architecture, with a case study to illustrate how it is simple yet e#ective to monitor and configure complex multimedia applications.

This paper describes the use of programming language constructs to support run-time software adaptation. A prototype language, Adaptive Java, contains primitives that permit programs to modify their own operation in a principled manner. In case studies, Adaptive Java is being used to support adaptation for different crosscutting concerns associated with heterogeneous mobile computing and critical infrastructure protection. Examples are described in which Adaptive Java components support dynamic quality-ofservice on wireless networks, run-time energy management for handheld computers, and self-auditing of potential security threats in distributed environments.

The convergence of data, voice and multimedia communication over digital networks, coupled with continuous improvement in network capacity and reliability has significantly enriched the ways we communicate. However, the stovepipe approach used to develop today’s communication applications and tools results in rigid technology, limited utility, lengthy and costly development cycle, difficulty in integration, and hinders innovation. In this paper, we present a fundamentally different approach, which we call Communication Virtual Machine (CVM) to address these problems. CVM provides a user-centric, modeldriven approach for conceiving, synthesizing and delivering communication solutions across application domains. We argue that CVM represents a far more effective paradigm for engineering communication solutions. The concept, architecture, modeling language, prototypical design and implementation of CVM are discussed.

This paper describes an experimental study in the use of a composable proxy framework to improve the quality of interactive audio streams delivered to mobile hosts. Two forward error correction (FEC) proxylets are developed, one using block erasure codes, and the other using the GSM 06.10 encoding algorithm. Separately, each type of FEC improves the ability of the audio stream to tolerate errors in a wireless LAN environment. When composed in a single proxy, however, they cooperate to correct additional types of burst errors. Results are presented from a performance study conducted on a mobile computing testbed.

A scalable middleware solution for QoS-aware multimedia service delivery in the ubiquitous computing environment remains a challenging problem. Its heterogeneous and dynamic nature demands a more flexible and intelligent framework. We present SMART, a self-reconfigurable component-based middleware solution to address this issue. The system responds to the reconfiguration requests from applications and users to offer extensibility and efficiency. Furthermore, we present an active controlling mechanism, in which the middleware is able to adapt to the environment variation in a timely fashion. In addition, we describe user management in our framework, which preserves our user-centric philosophy. Finally, we discuss MobiMan, an integrated multimedia service platform as the proof-of-concept application of SMART .

Abstract. Distributed multimedia applications are very sensitive to resource variations. An attractive way for dealing with dynamic resource variations consists in making applications adaptive, and even self-adaptive. The objective is to grant applications the ability to observe themselves and their environment, to detect significant changes and to adjust their behavior accordingly. This issue has been the subject of several works; however the proposed solutions lack flexibility and a high-level support that eases the development of adaptive applications. This paper presents PLASMA, a component-based framework for building multimedia applications. PLASMA relies on a hierarchical composition and reconfiguration model which provides the expected support. The experimental evaluation shows that adaptation can be achieved with a very low overhead, while significantly improving QoS of multimedia applications as well as resource usage on mobile equipments. 1.

This paper investigates the use of programming language constructs to realize adaptive behavior in support of collaboration among users of wearable and handheld computers. A prototype language, Adaptive Java, contains primitives that permit programs to modify their own operation in a principled manner. In a case study, Adaptive Java was used to construct MetaSocket components, whose composition and behavior can be adapted to changing conditions during execution. MetaSockets were then integrated into Pavilion, a web-based collaboration framework, and experiments were conducted on a mobile computing testbed containing wearable, handheld, and laptop computer systems. Performance results demonstrate the utility of MetaSockets to improving the quality of interactive audio streams and reliable data transfers among collaborating users.