Protocols for the efficient dissemination of context-aware messages

Context-aware applications are able to react and adapt to the context of their users. This context includes, for instance, location, properties of the user or their surroundings, nearby devices, etc. Over the last years, powerful mobile devices, i.e., smartphones or tablet computers, have become an important part in many people's computing life. Most of these devices maintain a continuous high-speed network connection, allowing to provide distributed applications with an uninterrupted stream of data. Additionally, a huge number of sensors, both in these mobile devices and deployed in our surroundings, enable the creation of comprehensive context models. Such large-scale context models open up new possibilities for the development of context-aware applications by providing access to relevant context information from providers all over the world. However, until now, applications need to query the context model for relevant information or register for events or messages; it is not possible to "push" information to the mobile devices, neither from the infrastructure nor from other mobile devices. To support application developers, we propose Contextcast, a novel communication paradigm that allows for the dissemination of context-aware (or contextual) messages in a system of context-aware routers. This includes the fundamental semantics to address clients using context constraints and a reference dissemination scheme for such messages. To enable Contextcast to grow to scales similar to the context-aware systems that it is intended to be used with, we also propose a couple of optimized routing approaches. They are designed to reduce the number of maintenance messages that are necessary for the dissemination of contextual messages. One optimized routing algorithm uses coarse context information to reduce the amount of context updates propagated to routers. To this end, routers use the similarity of contexts to automatically find groups of similar clients, whose information can then be propagated as a single, coarse context. While this reduces the amount of context information to be propagated, the resulting information loss causes more messages to be forwarded, since routers no longer possess exact information to match against the constraints in contextual messages. A configurable similarity threshold allows for various trade-offs between the coarseness of the context information and the resulting additional message load. The second orthogonal routing approach relies on statistics to determine the characteristics of contexts and messages in the system. Without context knowledge, routers must assume the presence of a matching recipient and forward a message speculatively to disseminate it to all recipients. Using statistics, routers can determine how often certain messages occur and then calculate the benefit of propagating contexts corresponding to these messages. Several parameters enable an administrator to adjust how fast the system reacts to changes, depending on the observed messages and context updates. Additionally, temporal support extends Contextcast with a powerful mechanism that allows application developers and clients to address messages to certain contexts in the past or future. This includes an additional context attribute \cattr{time} and a constraint with various, easy to use temporal operators. We also propose efficient routing approaches for historical and future messages. Routing historical messages focuses on efficient routing while effectively protecting the clients' privacy, i.e., their respective context history. The routing approach for future messages delays forwarding messages until a matching context is registered, thus preventing needlessly forwarded messages

Hybrid-Vehfog: A Robust Approach for Reliable Dissemination of Critical Messages in Connected Vehicles

Vehicular Ad-hoc Networks (VANET) enable efficient communication between vehicles with the aim of improving road safety. However, the growing number of vehicles in dense regions and obstacle shadowing regions like Manhattan and other downtown areas leads to frequent disconnection problems resulting in disrupted radio wave propagation between vehicles. To address this issue and to transmit critical messages between vehicles and drones deployed from service vehicles to overcome road incidents and obstacles, we proposed a hybrid technique based on fog computing called Hybrid-Vehfog to disseminate messages in obstacle shadowing regions, and multi-hop technique to disseminate messages in non-obstacle shadowing regions. Our proposed algorithm dynamically adapts to changes in an environment and benefits in efficiency with robust drone deployment capability as needed. Performance of Hybrid-Vehfog is carried out in Network Simulator (NS-2) and Simulation of Urban Mobility (SUMO) simulators. The results showed that Hybrid-Vehfog outperformed Cloud-assisted Message Downlink Dissemination Scheme (CMDS), Cross-Layer Broadcast Protocol (CLBP), PEer-to-Peer protocol for Allocated REsource (PrEPARE), Fog-Named Data Networking (NDN) with mobility, and flooding schemes at all vehicle densities and simulation times

Swarm-based Intelligent Routing (SIR) - a new approach for efficient routing in content centric delay tolerant networks

This paper introduces Swarm-based Intelligent Routing (SIR), a swarm intelligence based approach used for routing content in content centric Pocket Switched Networks. We first formalize the notion of optimal path in DTN, then introduce a swarm intelligence based routing protocol adapted to content centric DTN that use a publish/subscribe communication paradigm. The protocol works in a fully decentralized way in which nodes do not have any knowledge about the global topology. Nodes, via opportunistic contacts, update utility functions which synthesizes their spatio-temporal proximity from the content subscribers. This individual behavior applied by each node leads to the collective formation of gradient fields between content subscribers and content providers. Therefore, content routing simply sums up to follow the steepest slope along these gradient fields to reach subscribers who are located at the minima of the field. Via real traces analysis and simulation, we demonstrate the existence and relevance of such gradient field and show routing performance improvements when compared to classical routing protocols previously defined for information routing in DTN

GCP: Gossip-based Code Propagation for Large-scale Mobile Wireless Sensor Networks

Wireless sensor networks (WSN) have recently received an increasing interest. They are now expected to be deployed for long periods of time, thus requiring software updates. Updating the software code automatically on a huge number of sensors is a tremendous task, as ''by hand'' updates can obviously not be considered, especially when all participating sensors are embedded on mobile entities. In this paper, we investigate an approach to automatically update software in mobile sensor-based application when no localization mechanism is available. We leverage the peer-to-peer cooperation paradigm to achieve a good trade-off between reliability and scalability of code propagation. More specifically, we present the design and evaluation of GCP ({\emph Gossip-based Code Propagation}), a distributed software update algorithm for mobile wireless sensor networks. GCP relies on two different mechanisms (piggy-backing and forwarding control) to improve significantly the load balance without sacrificing on the propagation speed. We compare GCP against traditional dissemination approaches. Simulation results based on both synthetic and realistic workloads show that GCP achieves a good convergence speed while balancing the load evenly between sensors

Improving the Scalability of DPWS-Based Networked Infrastructures

The Devices Profile for Web Services (DPWS) specification enables seamless discovery, configuration, and interoperability of networked devices in various settings, ranging from home automation and multimedia to manufacturing equipment and data centers. Unfortunately, the sheer simplicity of event notification mechanisms that makes it fit for resource-constrained devices, makes it hard to scale to large infrastructures with more stringent dependability requirements, ironically, where self-configuration would be most useful. In this report, we address this challenge with a proposal to integrate gossip-based dissemination in DPWS, thus maintaining compatibility with original assumptions of the specification, and avoiding a centralized configuration server or custom black-box middleware components. In detail, we show how our approach provides an evolutionary and non-intrusive solution to the scalability limitations of DPWS and experimentally evaluate it with an implementation based on the the Web Services for Devices (WS4D) Java Multi Edition DPWS Stack (JMEDS).Comment: 28 pages, Technical Repor