A Layered Infrastructure for Mobility-Aware Best Connectivity in the Heterogeneous Wireless Internet

The common availability of wireless devices with multiple communication interfaces, e.g., IEEE 802.11, WiMAX, Bluetooth, and/or UMTS, is pushing towards the necessity of novel supports to seamlessly select the proper connectivity technology to exploit at any time. That selection should be context-dependent and consider several aspects, at very different abstraction layers, from application-specific bandwidth requirements to expected client mobility, from connectivity costs and energy consumption to user preferences. We claim the need of effective mobility-aware middleware solutions to relieve application logic from the burden of determining the most suitable interface and connectivity provider for each client at runtime. In particular, we claim that such middleware supports should be structured according to a two-layer architecture: a lower-layer facility to retrieve available interfaces and connectivity providers and to discard unsuitable ones with a per-node decision, e.g., to reduce power consumption; and a higher-layer facility to select the currently most suitable connectivity provider in a per-application way. The paper describes the design and implementation of our novel middleware built according to those architecture guidelines: that permits to clearly differentiate lower-level wireless interface management and connectivity evaluation from higher-level monitoring/selection, thus simplifying the separation between node- and application-specific requirements and the dynamic introduction of new connectivity evaluation metrics. In addition, to take mobility-aware connectivity decisions, our middleware effectively exploits the predicted degree of client node mobility, estimated in a completely autonomous decentralized way. The reported experimental results demonstrate the feasibility of the approach, with accurate estimations of node mobility associated with very limited overhead

A cross-layer middleware architecture for time and safety critical applications in MANETs

Mobile Ad hoc Networks (MANETs) can be deployed instantaneously and adaptively, making them highly suitable to military, medical and disaster-response scenarios. Using real-time applications for provision of instantaneous and dependable communications, media streaming, and device control in these scenarios is a growing research field. Realising timing requirements in packet delivery is essential to safety-critical real-time applications that are both delay- and loss-sensitive. Safety of these applications is compromised by packet loss, both on the network and by the applications themselves that will drop packets exceeding delay bounds. However, the provision of this required Quality of Service (QoS) must overcome issues relating to the lack of reliable existing infrastructure, conservation of safety-certified functionality. It must also overcome issues relating to the layer-2 dynamics with causal factors including hidden transmitters and fading channels. This thesis proposes that bounded maximum delay and safety-critical application support can be achieved by using cross-layer middleware. Such an approach benefits from the use of established protocols without requiring modifications to safety-certified ones. This research proposes ROAM: a novel, adaptive and scalable cross-layer Real-time Optimising Ad hoc Middleware framework for the provision and maintenance of performance guarantees in self-configuring MANETs. The ROAM framework is designed to be scalable to new optimisers and MANET protocols and requires no modifications of protocol functionality. Four original contributions are proposed: (1) ROAM, a middleware entity abstracts information from the protocol stack using application programming interfaces (APIs) and that implements optimisers to monitor and autonomously tune conditions at protocol layers in response to dynamic network conditions. The cross-layer approach is MANET protocol generic, using minimal imposition on the protocol stack, without protocol modification requirements. (2) A horizontal handoff optimiser that responds to time-varying link quality to ensure optimal and most robust channel usage. (3) A distributed contention reduction optimiser that reduces channel contention and related delay, in response to detection of the presence of a hidden transmitter. (4) A feasibility evaluation of the ROAM architecture to bound maximum delay and jitter in a comprehensive range of ns2-MIRACLE simulation scenarios that demonstrate independence from the key causes of network dynamics: application setting and MANET configuration; including mobility or topology. Experimental results show that ROAM can constrain end-to-end delay, jitter and packet loss, to support real-time applications with critical timing requirements