ABSTRACT The integration of distributed multimedia systems support into a communications architecture encompassing the new multiservice networks poses significatu challenges. A key observation about the new environment is that Quality of Service (QOS) provides a unifying theme around which most of the new communications requirements can be grouped. For applications relying on the transfer of multimedia information, and in particular continuous media, it is essential that QOS is guaranteed system-wide, including the distributed system pqorm, the tramport protocol and the multiservice network. Enhanced protocol support such as end-to-end QOS negotiation, renegotiation, indication of QOS degradations and co-ordination over multiple related connectwm are also required. Little attention, however, has so far been paid to the defw'tion of a coherent framework that incorporates QOS interfaces, management and mechanisms across all the layers. This paper describes the first stage in the development of an integrated Quality of Service Architecture (QOS-A) which offers a framework to specifr and implement the required performance properties of new multimedia applications over multiservice ATM-based networks. 1.

The desire to transfer continuous media such as digital audio and video across packet switched networks imposes a number of new requirements on transportlevel# communication services. This paper identifies a number of these requirements in the context of an experimental distributed multimedia infrastructure, and reports on research which addresses some of the associated issues. Particular attention is paid to two areas: (i) extended Quality of Service (QoS) provision; and (ii) support for the co-ordination of multiple related connections. We then describe an application level service, known as an orchestrator, which performs synchronisation functions over multiple related transport connections. We also outline the design and implementation of a continuous media transport service which meets the identified requirements. Finally, we outline the way in which the orchestrator and transport services are integrated into an object-based distributed multimedia application platform. 1. Introduc...

. Currently, popular operating systems are unable to support the end-to-end real-time requirements of distributed continuous media. Furthermore, the integration of continuous media communications software into such systems poses significant challenges. This paper describes a design for distributed multimedia support in the Chorus micro-kernel operating system environment which provides the necessary soft real-time support while simultaneously running conventional applications. Our approach is to extend existing Chorus abstractions to include QoS configurability, connection oriented communications and real-time threads. The design uses the following key concepts: the notion of a flow to represent QoS controlled communication between two application threads, a close integration of communications and thread scheduling and the use of a split level scheduling architecture with kernel and user level threads. The paper shows how our design qualitatively improves performance over existing micr...

The combination of high speed multi-service networks and multimedia workstations offers considerable potential for the development of distributed multimedia applications. However, many challenges remain before this potential can be realised. One key challenge is how to integrate continuous media types such as audio and video into a distributed workstation environment. This paper describes an experimental system architecture based on a specialised multimedia network interface that attempts to provide this integration. The design and implementation of this system is discussed in depth in terms of workstation enhancement and distributed system support. A new approach to the problem of media synchronisation is introduced, and the importance of Quality of Service in the architecture is highlighted. The paper also relates our experiences from this work, compares it with other approaches and outlines our views on likely future developments in multimedia network interfacing. 1. INTRODUCTION Mu...

ty (the QoS-A project) on an architectural approach to integrated QoS support for multimedia communications. 2 D. Hutchison, G. Coulson, A. Campbell and G.S. Blair 11.1. Introduction Recent years have seen dramatic advances in computer communications technology. At the network level, new high-speed technologies such as FDDI, DQDB and, most recently, ATM-based networks are becoming available. These networks not only have the capability to transmit information at high speed, but also offer a range of properties including bounded delay, guarantees on throughput and isochronous communications. Multimedia workstation technology for generating, compressing and displaying streams of digital video and audio is available in the marketplace in a range of price/performance categories, along with very high capacity storage systems such as CD-ROM. These technological developments are complemented by new user perspectives. New classes of distributed application are being de

Currently, popular operating systems are unable to support the end-toend real-time requirements of distributed continuous media. Furthermore, the integration of continuous media communications software into such systems poses significant challenges. This paper describes a design for distributed multimedia support in the Chorus micro-kernel operating system environment which provides the necessary soft real-time support while simultaneously running conventional applications. Our approach is to extend existing Chorus abstractions to include QoS configurability, connection oriented communications and real-time threads. The design uses the following key concepts: the notion of a flow to represent QoS controlled communication between two application threads, a close integration of communications and thread scheduling and the use of a split level scheduling architecture with kernel and user level threads. The paper shows how our design qualitatively improves performance over existing micro-k...

A real-time multimedia communication system over broadband networks is introduced in the paper. This system consists of distributed database servers which store and retrieve data objects of different types of media and in different coding formats. The multimedia document is transmitted over the network as streams through different connections and presented to the user simultaneously. A set of stream synchronization control schemes is designed to control the multiple data streams (either in coded or uncoded format) to achieve multimedia synchronization during progressive presentation. A centralized scheduler derives a stream delivery schedule to compensate variable network delay. The synchronization controller at a user's workstation performs synchronization error recovery by adjusting the presentation schedule according to the temporal requirements in the scenario. Skew tolerance parameters are employed as one of the synchronization requirements. In particular, MPEG-2 coded stream sync...

This work presents the proposal and the implementation of a multimedia synchronization service that offers facilities to real time communication and presentation of pre-orchestrated multimedia information, that is stored in remote data bases. As a basis for synchronization mechanisms, the eXtended Object Composition Petri Net (XOCPN) has been employed. The target application is described, the synchronization service is defined by its service primitives and the protocol is specified through its data unit's types and field formats. A high performance implementation architecture has been used, defining specialized modules of priority-based task scheduling, optimized memory management and timer management. This paper also presents the definition of the data structures for the XOCPN model and an implementation diagram of the synchronization's mechanism, describing some procedures of the XOCPN-related synchronization's modules.

this paper, we do not consider constant bit rate streams, but focus on VBR streams where there is need for sophisticated management of flow to accommodate the variability in the use of bandwidth and client buffering

The support for a video conference session recording provides the capability of saving video frames when the quality of service becomes unacceptable or when some of the recipients become unreachable. A user may want to store the conference session to be able to review/edit it later. Efficient retrieval of a session recorded at a remote user's site requires integration of video conferencing software with a video-on-demand (VOD) system. We present the design and implementation of a prototype distributed VOD system that supports efficient continuous video delivery over the Internet. We describe its integration with video conferencing tool, developed at XEROX PARC, called Network Video (NV) [Fre94]. To achieve high performance in video delivery, this VOD prototype employs features such as client-server paradigm, dynamic buffering, and request-on-demand techniques. 1 Introduction Efficient replay and retrieval of video conferencing session recordings by remote users require involvement of ...