Abstract. Next-generation Grid applications will be highly heterogeneous in nature, will run on many types of computer and device, will operate within and across many heterogeneous network types, and must be explicitly configurable and runtime reconfigurable. We refer to this future Grid environment as the “divergent Grid”. In this paper, we propose a “deep middleware ” approach to meeting key requirements of the divergent Grid. Deep middleware reaches down into the network to provide highly flexible network support that underpins a rich, extensible and reconfigurable set of application-level “interaction paradigms ” (such as publish-subscribe, multicast, tuple spaces etc.). In our Gridkit middleware platform, these facilities are encapsulated in two key component frameworks: the interaction framework and the overlay framework, which are the subject of this paper. The paper also evaluates the two frameworks in terms of their configurability (e.g. ability to be profiled for different device types) and reconfigurability (e.g. to self-optimise as the environment changes). 1

We present and evaluate a generic approach to the repair of overlay networks which identifies general principles of overlay repair and embodies these as a reusable service. At the heart of our approach is an algorithm that discovers the extent of a failed section of any type of overlay, and assigns responsibility to carry out the repair. The repair strategy itself is ‘pluggable ’ and can be tailored to the requirements of a specific overlay type or instance. Our approach is efficient in terms of the number of repair-related message exchanges it incurs; scalable in that it involves only nodes in the locality of the failed section of the overlay; and resilient in that it correctly handles cases in which multiple adjacent nodes fail simultaneously, and it tolerates new failures that occur while a repair is underway. The benefits of our approach are that: (i) it extracts and encapsulates best practice in repair for overlays; (ii) it simplifies the design and implementation of new overlays (because repair issues can be treated orthogonally to basic functionality); and (iii) it supports tailorable levels of dependability for overlays, including pluggable repair strategies. 1.

Abstract. Use of web services also on mobile devices becomes increasingly relevant. However, realizing such mobile web services based on the standard protocol stack is often inappropriate for resource-restricted mobile devices in dynamic networks. On the other hand, using specialized alternative protocols restricts compatibility with traditional service applications. Thus, existing approaches often do not allow to integrate heterogeneous service instances dynamically, as it is, e.g., required for executing mobile service-based business processes. In order to adequately support such more complex and dynamic applications, this paper presents a lean and flexible system architecture which supports both mobile web service consumers and providers by allowing to integrate multiple protocols depending on their capabilities and to dynamically access suitable service instances at runtime. As a proof of concept, the paper shows an exemplary combination of practically relevant protocols for resource-limited devices based on WSDL, ASN.1 and overlay transport and presents its integration in a prototype scenario for supporting decentralized mobile business processes. 1

Current research trends in networks and telecommunications suggest that future architectures will aim for the convergence not only of fixed and mobile infrastructures, but also of different network layer technologies. Proposals like OCALA from UC Berkeley and our own TRANSIT can be used to converge different architectures and network layer overlays while supporting legacy applications. In this paper we analyse and assess the security threats against such systems. Our contribution constitutes the first step in designing security models for convergence architectures as part of their design and deployment phases, rather than as retrofitted mechanisms. 1.

IP Multicast holds great promise for the Internet in the near future. With the explosion in the multimedia content providers, very soon current Internet infrastructure will begin to feel the pressure due to higher bandwidth demands that may limit the content provider subscriber base and / or limit the quality of the stream. Multicast is best suited to address such concerns of scale and efficient network bandwidth utilization. One of the limiting factors that have stopped widespread Multicast deployment is the lack of global session’s directory structure. Ubiquitous URLs along with the DNS infrastructure which has been a major factor for fast and increasing popularity of the Internet and the lack thereof for the Multicast points towards one of the last stumbling blocks for its widespread deployment. 0.1.2 Research Goals • Proposal for a global and scalable Multicast session directory architecture • Design of user friendly URLs for various Multicast Streams • Efficient Multicast address allocation infrastructure

Abstract — This paper describes our work on real-time twoparty and multi-party VoIP (voice-over-IP) systems that can achieve high perceptual conversational quality. It focuses on the fundamental understanding of conversational quality and its trade-offs among the design of speech codecs and strategies for network control, playout scheduling, and loss concealments. We have studied three key aspects that address the limitations of existing work and improve the perceptual quality of VoIP systems. Firstly, we have developed a statistical approach based on just-noticeable difference (JND) to significantly reduce the large number of subjective tests, as well as a classification method to automatically learn and generalize the results to unseen conditions. Using network and conversational conditions measured at run time, the classifier learned helps adjust the control algorithms in achieving high perceptual conversational quality. Secondly, we have designed a cross-layer speech codec to interface with the loss-concealment and playout scheduling algorithms in the packet-stream layer in order to be more robust and effective against packet losses. Thirdly, we have developed a distributed algorithm for equalizing mutual silences and an overlay network for multi-party VoIP systems. The approach leads to multi-party conversations with high listening only speech quality and balanced mutual silences.

Nowadays, a very useful platform is becoming widely used to deploy new services and applications in the Internet: the overlay networks. These networks create a virtual topology on top of existing ones with the purpose of providing several different services such as file sharing or content delivery. This survey focuses on diverse research issues concerning overlay networks applicability and management strategies required for emergent network environments. In this way, mobility, security, scalability, dependability and resource constraints are studied with regard to overlay networks. We finally discuss the evolution of these networks in order to satisfy new technological improvements.