ECCO : data centric asynchronous communication

The thesis of this dissertation deals with ubiquitous and wireless pervasive computing. The main focus is on data centric networking in distributed systems, which relies on content addressing instead of host addressing for participating nodes, thus providing network independence for applications. Publish/subscribe asynchronous group communication realises the vision of data centric networking that is particularly important for networks supporting mobile clients over heterogeneous wireless networks. In such networks, client applications prefer to receive specific data, requiring selective data dissemination. Underlying mechanisms such as asynchronous message passing, distributed message filtering and query/subscription management are essential requirements. Furthermore, recent progress in wireless sensor networks brought a new dimension of data processing in ubiquitous computing, where the sensors are used to gather high volumes of different data types and to feed them as contexts to a wide range of applications. This data processing requires advanced mechanisms that make intelligent use of simple data to create meaningful information. The following specific subjects in ubiquitous computing environments are addressed. Particular emphasis has been placed on fundamental design of event representation. Besides the existing event attributes, event order, and continuous context information such as time or geographic location could be incorporated within an event description. Data representation of event and query will be even more important in future ubiquitous computing, where events flow over heterogeneous networks. This dissertation presents a multidimensional event representation (i.e., Hypercube structure in RTree) for efficient indexing, filtering, matching, and scalability in publish/subscribe systems. The hypercube event with a typed content-based publish/subscribe system for wide-area networks is demonstrated for improving the event filtering process. As a primary focus, this dissertation investigates a structureless, asynchronous group communication over wireless ad hoc networks named ECCO* Pervasive Publish/Subscribe (ECCO-PPS). ECCO-PPS uses a context adaptive controlled flooding, which takes a cross layer approach between middleware and network layer and provides a content-based publish/subscribe paradigm. Traditionally events have been payload data within network layer components; the network layer never touches the data contents. However, application data have more influences on data dissemination in ubiquitous computing scenarios. The state information of the local node may be the event forwarding trigger. Thus, the model of publish/subscribe must become more symmetric, with events being disseminated based on rules and conditions defined by the events themselves. The event can thus choose the destinations instead of relying on the potential receivers’ decision. The publish/subscribe system offers a data centric approach, where the destination address is not described with any explicit network address. The symmetric publish/subscribe paradigm brings another level to the data centric paradigm, and this new paradigm leads to a fundamental change of the functionality at the network level of asynchronous group communication and membership maintenance. Dynamic channelisation by clustering the subscriptions is also attempted. To add an additional dimension of event processing in global computing, understanding event aggregation, filtering and correlation is an important issue. Event correlation is discussed as part