The Internet is undergoing substantial changes from a communication and browsing infrastructure to a medium for conducting business and marketing a myriad of services. The World Wide Web provides a uniform and widely-accepted application interface used by these services to reach multitudes of clients. These changes place the web server at the center of a gradually emerging eservice infrastructure with increasing requirements for service quality and reliability guarantees in an unpredictable and highly-dynamic environment.

The proliferation of communication-intensive real-time applications with "elastic" real-time constraints, such as streaming stored video, and the advent of differential services over the Internet require a new design for end-host communication subsystems. The design should (i) provide per-flow or per-service-class guarantees on the end-host, (ii) maximize the aggregate utility (or revenue) of the end-host's communication service across all clients, (iii) gracefully adapt to transient overload and resource shortage, and (iv) not starve lower-priority service classes during the period of sustained overload. This paper presents a new architecture for QoS-adaptive end-host communication subsystems in order to meet the above-stated goals. This architecture differs from others in that it provides generic end-host communication subsystem support for QoS-adaptive communication, as opposed to devising QoS adaptation for a particular type of real-time applications. Our architecture provides each...

The advent of QoS-sensitive Internet applications such as multimedia, the inception of priced online services, and the proliferation of performance-critical applications such as online trading raise a need for building server systems with guaranteed performance. Unlike embedded software systems designed for a particular special-purpose platform, the new applications should be designed to run on different heterogeneous platforms, provide soft performance guarantees commensurate with platform capacity, and adapt efficiently to upgrades in platform resources over the system's lifetime. The problem of profiling the application for the purposes of providing QoS guarantees on each new platform becomes a significant undertaking. Automated profiling mechanisms must be built to enable efficient computing of QoS guarantees tailored to platform capacity and facilitate wide deployment of soft performance-guaranteed systems on heterogeneous platforms.

The advent of performance-critical services such as online brokerage and e-commerce, as well as QoS-sensitive services such as streaming multimedia, makes existing FIFO servers incapable of meeting application QoS requirements. Re-designing server code to support QoS provisioning, on the other hand, is costly and time-consuming. To remedy this problem, we propose a new QoS-provisioning approach that does not require modification of server and OS code. We develop a middleware, called qContracts, that can be transparently interposed between the server process and the operating system to achieve performance differentiation and soft QoS guarantees. The middleware enables reuse of existing legacy software in QoS-sensitive contexts, and off-loads QoS management concerns from future real-time service programmers. As an example, we show how the Apache [9] web server is endowed with QoS support using qContracts on UNIX. Experimental results show the efficacy of the middleware in achieving the c...

In this paper, we derive a utilization bound on schedulability of apriodic tasks with arbitrary arrival times, execution times, and deadlines. To the author's knowledge, this is the first time a utilization bound is derived for the aperiodic task model. It allows constructing an O(1) admission test for aperiodic tasks. Earlier admission tests are at best O(n). We show that deadline-monotonic scheduling is the optimal fixed-priority scheduling policy for aperiodic tasks in the sense of maximizing the schedulable utilization bound. We prove that the optimal bound is 5=8. Our result is an extension of the well-known Liu and Layland's bound of ln 2 (derived for periodic tasks). The new bound is shown to be tight. We briefly generalize our results to tasks with multiple resource requirements and multiple processors. Dynamic priority scheduling (EDF) of aperiodic tasks is shown to have the same schedulability bound as for periodic tasks. Our findings are especially useful for an emerging ca...

This paper proposes a new ATM multicast scheme within the framework of an Active Multicast Service Architecture (AMSA) that supports user customization of multicast service. The customization is achieved by injecting and invoking user specific programs to shared network resources such as routers and switches. The multicast scheme also allows dynamic joining and (or) leaving of members of different capabilities and quality of service requirements. A prototype of the multicast scheme was developed to verify the major functions of the AMSA and to demonstrate the feasibility of customizing network services within the active service architectural framework . The prototype supports QOS negotiation, non-uniform links QOS, resource reservation and filter program injection. The development platform used consists of virtual ATM switches (implemented as light-weight threads in four workstations for simulating real ATM switches) interconnected via a real FORE ATM switch. The data links between the...

QOS ADAPTATION IN REAL-TIME SYSTEMS by Tarek F. Abdelzaher Chair: Kang G. Shin We propose to design, implement, and evaluate a software framework, called the Adaptware, that consists of architectural support, resource-management mechanisms, and programming abstractions for adapting Quality-of-Service (QoS) to dynamically-fluctuating resource capacity and demands. This framework is to reduce the cost and time of real-time software development by providing the infrastructure necessary for building reusable multi-purpose real-time software components. In much the same way as today's consumers can buy software and hardware components from different vendors and construct a computing environment tailored to their needs, the proposed framework will provide the means of building and integrating real-time system components so as to preserve their temporal correctness while making it possible to dynamically compute predictable end-to-end temporal guarantees commensurate with available resour...

. A next generation distributed system is expected to be flexible in the sense that the system is able to deal with various changes of both the users' requirements and the operational conditions of system's environment. The aim of our research is to establish a new design methodology of the flexible distributed systems based on agent-based computing technology. To do so, we propose an agent-based distributed information processing system (ADIPS) as a design model of flexible distributed systems. Furthermore, we have developed an agent-based computing framework called ADIPS Framework which supports the design and implementation of flexible distributed systems. In this paper, we discuss the architecture and functions of ADIPS Framework together with the applications realized by using ADIPS framework. 1 Introduction The next generation distributed systems have to provide various services for the users living in the networked information spaces realized on the large-scale distr...

Introduction Recently the demand for real-time database services is exploding. The applications requiring such services include sensor data fusion, decision support, web information service, e-commerce, online trading, and dataintensive smart space applications. Furthermore, the information system is being globalized due to the fast growth of the Internet. Despite the importance and wide applicability, the performance and predictability of a database system \Gamma the core component of global information systems \Gamma are relatively limited compared to the other real-time systems such as real-time operating systems. It can not be easily replicated due to the consistency problem. In addition, the database system has relatively low predictability compared to other real-time systems due to data dependence of the transaction execution, data and resource conflicts, dynamic paging and I/O, and transaction aborts and the resulting rollbacks and restarts [36]. Because of the limited perfo

We present a QoS architecture for collaborative virtual environments (CVEs), focusing on the management of streamed video within shared virtual worlds. Users express QoS requirements by negotiating levels of mutual awareness using our previously defined spatial model of interaction. The architecture uses these awareness values as part of dynamic QoS management. A key aspect of the architecture is that it maintains a balance between the needs of a group of users as a whole (e.g., which streams are admitted onto a shared network) versus those of individual users within the group (e.g., which streams are subscribed to by a local host). We walk through a demonstration scenario, a virtual shopping mall, to show the architecture at work.