Event detection is a major issue for applications of wireless sensor networks. In order to detect an event, a sensor network has to identify which application-specific incident has occurred based on the raw data gathered by individual sensor nodes. In this context, an event may be anything from a malfunction of monitored machinery to an intrusion into a restricted area. The goal is to provide high-accuracy event detection at minimal energy cost in order to maximize network lifetime. In this paper, we present a system for collaborative event detection directly on the sensor nodes. The system does not require a base station for centralized coordination or processing, and is fully trainable to recognize different classes of application-specific events. Communication overhead is reduced to a minimum by processing raw data directly on the sensor nodes and only reporting which events have been detected. The detection accuracy is evaluated using a 100node sensor network deployed as a wireless alarm system on the fence of a real-world construction site.

A broadcast mode may augment peer-to-peer overlay networks with an efficient, scalable data replication function, but may also give rise to a virtual link layer in VPN-type solutions. We introduce a generic, simple broadcasting mechanism that operates in the prefix space of distributed hash tables without signaling. This paper concentrates on the performance analysis of the prefix flooding scheme. Starting from simple models of recursive $k$-ary trees, we analytically derive distributions of hop counts and the replication load. Further on, extensive simulation results are presented based on an implementation within the OverSim framework. Comparisons are drawn to Scribe, taken as a general reference model for group communication according to the shared, rendezvous-point-centered distribution paradigm. The prefix flooding scheme thereby confirmed its widely predictable performance and consistently outperformed Scribe in all metrics. Reverse path selection in overlays is identified as a major cause of performance degradation.

Recent efforts are made to construct a globally accessible group communication service by a simultaneous use of network and application layer multicast. Such hybrid approaches provide native multicast to group members wherever available, but relocate data distribution and duplication from the network to applications or gateways if needed. Such services require an abstract programming interface to allow for a transparent use by applications. The contributions of this paper are twofold. First, we explore the problem space of designing a protocol stack for hybrid group communication that covers structured P2P networks. Second, we propose a transparent API that encapsulates a middleware abstraction layer for implementing hybrid multicast, and allows for overlay-underlay agnostic programming.

IPTV, software replication and other large-scale distribution tasks urge the need for efficient multicast mechanisms in overlay networks. Current multicast solutions on the application layer are either efficient, structured, but inflexible, or flexible, unstructured, but of lesser efficiency. This paper introduces scalable adaptive multicast on bi-directional shared trees, a new structured but flexible approach to content distribution. BIDIRSAM is the first DHT-based overlay multicast that distributes any source multicast data according to source-specific shortest path trees. Built upon bi-directional shared prefix trees, the approach distributes packets uniquely via fully redundant paths, and allows for highly flexible network adaptivity. Guided by an overlay abstraction, it operates directly on top of a prefix routing and does not rely on any kind of rendezvous point or bootstrapping.

Service placement deals with the problem of selecting which node in a network is most suitable for hosting a service that responds to queries from other nodes. Optimally placing services reduces network traffic and improves connectivity between clients and servers. Service placement algorithms may thus be regarded as an interesting building block for research into service-oriented middleware. Recently, new approaches to address the service placement problem in the field of ad-hoc networking have been proposed. This paper surveys, classifies and evaluates ten representative approaches, thereby providing a summary of the state of the art in service placement.

In order to avoid transmitting raw data to a base station, sensor nodes are trained to cooperatively recognize deployment-specific events based on the data sampled by their sensors. As both training and event detection are performed without the need for central coordination or processing, only information about the detected event needs to be reported.