No abstract

No abstract

The long awaited 'new environment' of high speed broadband networks and multimedia applications is fast becoming a reality. However, few systems in existence today, whether they be large scale pilots or small scale test-beds in research laboratories, offer a fully integrated and flexible environment where multimedia applications can maximally exploit the quality of service (QoS) capabilities of supporting networks and end-systems. In this paper we describe the implementation of an adaptive transport system that incorporates a QoS oriented API and a range of mechanisms to assist applications in exploiting QoS and adapting to fluctuations in QoS. The system, which is an instantiation of the Lancaster QoS Architecture, is implemented in a multi ATM switch network environment with Linux based PC end systems and continuous media file servers. A performance evaluation of the system configured to support video-on-demand application scenario is presented and discussed. Emphasis is placed on novel features of the system and on their integration into a complete prototype. The most prominent novelty of our design is a 'distributed QoS adaptation' scheme which allows applications to delegate to the system responsibility for augmenting and reducing the perceptual quality of video and audio flows when resource availability increases or decreases.

Because of the increasingly diverse and dynamic environments in which they must operate, modern middleware platforms need to explicitly support modifiability. Modifiability should encompass change that is both static and dynamic; small scale and large scale. Also, the process of modification should be flexible, easy to perform, and consistency-preserving. To address these needs, this paper proposes a generic component-based modifiability approach, and then uses this approach to build a highly-modifiable middleware framework. The modifiability approach provides design support for building component frameworks-i.e., reusable and extensible component architectures that are targeted at specific domains. In the approach, component frameworks build upon a minimal, technology-independent component model, and can be recursively assembled into more complex frameworks. Our middleware framework-an instantiation of our proposed approach-takes the form of a specific assembly of component frameworks, each of which addresses a distinct middleware-related concern. Our middleware framework supports two styles of modification: First, 'architectural modification' enables large-scale, static, changes, such as customizing the framework to a new application domain or underlying infrastructure. Second, 'system modification' enables changes that are based on specific customisations of the framework; these changes are 2 smaller in scope (e.g. replacing protocol implementations) but are applicable at both deploytime and run-time. A prototype implementation demonstrates the feasibility of our approach and framework, and demonstrates a sufficient degree of supported modifiability. 1 We use the term 'modifiable middleware' rather than 'adaptive middleware' because it is a more general term; in particular, it covers large-scale, static modification, not typically addressed by adaptive middleware.

Peer-to-peer file sharing has become popular for many kinds of resource location and distribution applications including file sharing, distributed computation, multi-media messaging and content distribution. Peer-to-peer approaches also have significant potential for supporting large scale, decentralised service oriented computing. This chapter discusses each class of contemporary P2P architecture in turn and discusses the suitability of each architecture class for supporting service oriented computing. Future trends in peer-to-peer architectures are then discussed and multi-layer peer-topeer architectures are highlighted as a promising platform for supporting service oriented computing. This chapter then concludes with a discussion of outstanding issues that must be addressed before peer-to-peer architectures can offer adequate support for service oriented computing.