A Peer-to-Peer Approach to Content-Based Publish/Subscribe

Publish/subscribe systems are successfully used to decouple distributed applications. However, their e#ciency is closely tied to the topology of the underlying network, the design of which has been neglected. Peer-to-peer network topologies can o#er inherently bounded delivery depth, load sharing, and self-organisation. In this paper, we present a contentbased publish/subscribe system routed over a peer-to-peer topology graph. The implications of combining these approaches are explored and a particular implementation using elements from Rebeca and Chord is proven correct

A Model Driven Architecture for Adaptable Overlay Networks

Recent years have witnessed a remarkable spread of interest in decentralised infrastructures for Internet services. Peer-to-Peer systems and overlay networks have given rise to a major paradigm shift and to novel challenges in distributed systems research. Numerous projects from several research communities and commercial organisations have started building and deploying their own systems. Adoption, however, has been restricted to sparsely selected areas, dominated by few applications. Among the technical reasons for the limited availability of deployable systems is the complexity of their design and the incompatibility of systems and frameworks. Applications are tightly coupled to a specific overlay implementation and the framework it uses. This leaves developers with two choices: implementing their application based on the fixed combination of overlay, networking framework and programming language, or reimplementing the overlay based on the desired application framework. Both approaches have their obvious draw-backs. Implementing an overlay, even as a reimplementation, is a task that exhibits considerable challenges. Protocols have to be adapted, completed and partially reverse engineered from the original system to implement them correctly. Message serializations and interfaces have to be rewritten for the new framework. State maintenance and event handling are programmed in very different ways in different environments, which typically requires their redesign. Reimplementing an overlay for a new environment is therefore not necessarily less work than designing a new one. As for the alternative, being tied to a specific environment prevents the application designer from freely choosing the best suited framework for the specific application. Deploying different overlays in one application is only possible if they were written for the same framework, and even then, running multiple non-integrated overlays at the same time can become prohibitively resource extensive. Testing with different overlay topologies and adapting to different deployment environments is similarly hard in this scenario. The current techniques used for overlay implementation turn out to become limiting factors in the design of overlay applications. The approach taken by this thesis tackles these issues at design time, at a point long before integration problems arise. It presents a modelling framework that allows to express overlay specific semantics in a platform-independent, domain specific language called the Overlay Modelling Language, OverML. A Model Driven Architecture maps these abstract overlay specifications to concrete, framework specific implementations. Applications based on OverML benefit from state sharing between different overlays and from short topology implementations in the SQL-Like Overlay Specification Language SLOSL. Their conciseness allows an easy adaptation of SLOSL statements to specific quality-of-service requirements. The architecture provides a clean separation between the generated implementation and hand-written components through generic, event-driven interfaces. To evaluate the approach, a series of topologies is exemplarily specified in OverML and/or SLOSL. A complete walk-through from the specification to the deployment of an OverML implemented overlay is additionally presented. The major contribution of this thesis is the first complete design methodology for the integrative, high-level development of portable, adaptable overlay networks

Overlay networks - implementation by specification

Implementing overlay software is non-trivial. Current projects build overlays or intermediate frameworks on top of low-level networking abstractions. This leaves implementing the topologies, their maintenance and optimisation strategies, and the routing to the developer

Models and Languages for Overlay Networks

Implementing overlay software is non-trivial. In current projects, overlays or frameworks are built on top of low-level networking abstractions. This leaves the implementation of topologies, their maintenance and optimisation strategies, and the routing entirely to the developer

Databases and Distributed Systems Group,

Abstract — Publish-subscribe is a powerful paradigm for distributed communication based on decoupled producers and consumers of information. Its event-driven nature makes it very appealing for large-scale data dissemination infrastructures. Various architectures were proposed in recent years that provide very diverse features. However, there are few well-defined metrics in the publish-subscribe area that would allow their evaluation and comparison. In this paper, we provide a broad overview of relevant quality-of-service metrics and describe their specific meaning in the context of distributed and decentralized publish-subscribe systems. Our goal is to provide a common base for future evaluations of emerging systems and for the design of qualityof-service aware publish-subscribe infrastructures. I