This paper presents the design, implementation and experimental analysis of a distributed real-time MPEG video audio player. Section 2 describes the overall system architecture. Section 3 discusses the software feedback, synchronization, and QoS control mechanisms adopted in the player. Sections 4 then describes the implementation and presents some initial performance results. Related work is outlined in Section 5. Finally, Section 6 discusses future work and concludes the paper. 2 System Architecture

. Distributed object middleware, such as CORBA, hides systemand network-specific characteristics of objects behind functional interface specifications. This simplifies development and maintenance of distributed objects, contributing to their growing acceptance. Critical applications have Quality of Service (QoS) requirements, however, such as real-time performance, dependability, or security, that are hidden by middleware. Because of this, application developers often bypass distributed object systems, thus gaining little or no advantage from the middleware. We have developed Quality Objects (QuO), a framework for developing distributed applications with QoS requirements. QuO provides a set of aspect languages, called Quality Description Languages (QDL), for specifying possible QoS states, the system resources and mechanisms for measuring and controlling QoS, and behavior for adapting to changing levels of available QoS at runtime. This paper describes QuO's aspect languages, their usa...

This paper describes the design and implementation of a real-time, streaming, Internet video and audio player. The player has a number of advanced features including dynamic adaptation to changes in available bandwidth, latency and latency variation; a multi-dimensional media scaling capability driven by user-specified quality of service (QoS) requirements; and support for complex content comprising multiple synchronized video and audio streams. The player was developed as part of the QUASAR + project at Oregon Graduate Institute, is freely available, and serves as a testbed for research in adaptive resource management and QoS control. Keywords: Internet, video, real-time, MPEG, adaptive, feedback, quality of service 1. INTRODUCTION Digital multimedia systems are becoming ubiquitous, with nearly all computer platforms offering support for realtime datatypes such as audio and video. There has also been a rapid proliferation of communications networks, giving multimedia computing th...

In this paper, we revisit and challenge the dogma that TCP is an undesirable choice for streaming multimedia, video in particular. For some time, the common view held that neither TCP nor UDP, the Internet's main transport protocols, are adequate for video applications. UDP's service model doesn't provide enough support to the application while TCP's provides too much. Consequently, numerous research works proposed new transport protocols with alternate service-models as more suitable for video. For example, such service models might provide higher reliability than UDP but not the full-reliability of TCP. More recently, study of Internet dynamics has shown that TCP's stature as the predominant protocol persists. Through some combination of accident and design, TCP's congestion avoidance mechanism seems essential to the Internet's scalability and stability. Research on modeling TCP dynamics in order to e#ectively define the notion of TCP-friendly congestion avoidance is very active. Meanwhile, proposals for video-oriented transport protocols continue to appear, but they now generally include TCPfriendly congestion avoidance. Our concern is over the marginal benefit of changing TCP's service model, given the presence of congestion avoidance. As a position paper, our contribution will not be in the form of final answers, but our hope is to convince the reader of the merit in reexamining the question: do applications need a replacement for TCP in order to do streaming video? 1

In this paper, we introduce an XML-based Hierarchical QoS Markup Language, called HQML, to enhance distributed multimedia applications on the World Wide Web (WWW) with Quality of Service (QoS) capability. The design of HQML is based on two observations: (1) the absence of a systematic QoS specification language, that can be used by distributed multimedia applications on the WWW to utilize the state-of-the-art QoS management technology; and (2) the power and popularity of XML to deliver richly structured contents over the Web. HQML allows distributed multimedia applications to specify all kinds of application-specific QoS policies and requirements. During runtime, the HQML Executor translates the HQML file into desired data structures and cooperates with the QoS proxies that assist applications in end-to-end QoS negotiation, setup and enforcement. In order to make QoS services tailored toward user preferences and meet the challenges of uncertainty in the distributed heterogeneous environments, the design of HQML is featured as interactive and flexible. In order to allow application developers to create HQML specifications correctly and easily, we have designed and developed a unified visual QoS programming environment, called QoSTalk. In QoSTalk, we adopt a grammatical approach to perform consistency check on the visual QoS specifications and generate HQML files automatically. Finally, we introduce the distributed QoS compiler, which performs the automatic mappings between application and resource level QoS parameters to relieve the application developer of the burden of dealing with low level QoS specifications. keywords Quality of Service, XML, Distributed Multimedia Applications, Visual Programming Environment 1

This paper describes problems and solutions for delivering real-time, multi-media presentations across the Internet. A key characteristic of presentations of continuous media datatypes, such as digital video and audio, is their need for predictable real-time data delivery. For example, an NTSC quality video presentation requires video frames to be displayed every 1/30th of a second. Variations in this display rate can be observable as stalls or glitches in the video stream and reduce the quality of the presentation [6]. Delivering such presentations across the Internet is difficult because highly variable bandwidth and latency make it difficult to predict the arrival time of network packets containing video or audio data. Our solution is for distributed multi-media systems to adapt dynamically to these changing network conditions. This paper describes the use of software feedback

Specialization is a technique that has the potential to provide operating system clients with the performance and functionality that they need, while still retaining the advantages of a simple generic code base for the operating system maintainer. However, at present the specialization process is labor-intensive and requires the knowledge of an expert in the domain of application behavior. In order to realize the full advantages of specialization, we believe that the process must be automated. This means building tools for specialization, and also making the domain knowledge explicit in some form or other. A specialization toolkit has been developed jointly at the Oregon Graduate Institute and IRISA, as part of the Synthetix project. This paper discusses our preliminary ideas on the use of Microlanguages to describe application behavior and to make that information available to the specialization tools. 1

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INTRODUCTION Modern workstation and network technology has made software-only solutions feasible for real-time playback of compressed continuous video and audio across the Internet. The Internet environment is characterised by widespread resource sharing, dynamic workload, great diversity in host processing speed and network bandwidth, no end-to-end resource reservation facility, and lack of a common clock. To meet the strict timing requirements of distributed multimedia presentation in the face of such characteristics requires new approaches to client/server synchronization, Quality-of-Service (QoS) control and system adaptiveness. Client/server synchronization can be achieved through external mechanisms like the Network Time Protocol (NTP). Such protocols are not ubiquitous on the Internet, and so it is necessary for applications to implement their own mechanisms. Similarly, QoS guarantees can be provided with admission control and resource reservation. However, such approac

Adaptation is a key technique in constructing survivable information systems. Allowing a system to continue running, albeit with reduced functionality or performance, in the face of reduced resources, attacks, or broken components is often preferable to either complete shutdown or continued normal operation in compromised mode. However, unpredictable adaptation can sometimes be worse than the problem it seeks to cope with. In this paper we introduce adaptation spaces, which precisely and predictably specify the adaptation of a software component. We then present two survivable systems that have been specified and implemented using adaptation spaces. The first example uses user preferences regarding quality in an audio application to guide the adaptation when available bandwidth decreases. The second trades off performance overhead with intrusion resistance for "stack-smashing" attacks. We formally define an adaptation space and show briefly how it enables certain kinds of reasoning about adaptive applications. We conclude with related work and future plans.