Delay Tolerant Networking is an approach to networking that supports routing in the absence of a contemporaneous end-to-end path between a source and its destination. The concept came out of research into Interplanetary Networks, which support communication between planets by anticipating and utilising the orbital alignment of links along a path. DTN has since been generalised to address other challenging environments including battlefield networks, third world infrastructure provision and wildlife monitoring. This thesis considers the use of a new networking paradigm for data collection, a specialisation of Delay Tolerant Networking, known as Pocket Switched Networks. Pocket Switched Networks use short-hop networking technologies, opportunistic interactions between human-carried devices and human mobility to forward data, hop by hop to its destination. Studies have shown that, in theory, PSN can provide a cheap, infrastructure-free, best effort, high- latency support for applications. However, there are several problems faced by researches when it comes to designing and evaluating PSN protocols. First, there is a lack of compelling mainstream PSN (and even DTN) applications which makes it hard to evaluate PSN protocols within a realistic or widely accepted context. Second, it is hard to 'join up' theory with practice, for example there are few examples of results from practical deployments being reapplied within a theoretical context. Third, there are many inter-related dependencies that come from both the reliance on opportunistic contacts (i.e. human behaviour) and the use of commodity devices. The literature rarely accounts for the impact of workload, architecture, protocol, pragmatic and technical issues upon end performance. This thesis tackles the challenge of studying Pocket Switched Networks in light of these problems. The thesis responds to the challenge by presenting, using and reflecting upon a structured approach to the design and evaluation of PSN protocols. The approach consists of an application bootstrapping phase, a trace-based simulation phase and a deployment stage each of which iteratively informs the others. The thesis demonstrates the use of this structured approach in the design and evaluation of a novel anycast PSN protocol; HEATS/NI(, which utilises a metric of prior encounters with data 'sinks' in its routing decisions. When compared against optimal results in simulation, using Bluetooth traces collected over nine-months from a hundred devices, it performs well and outperforms protocols that do not leverage the repeating patterns of human movement. More generally the results, in both simulation and deployment, show that the contact distributions from a sparse social graph are sufficient to support routing and that stable paths can be created using a metric that leverages the structure inherent in human mobility. Our results confirm that the use of intermediate nodes as carriers in sparse networks provides a performance improvement over direct contact schemes. In order to support the simulation and deployment stages of the structured approach, we present a set of design principles that emerge from the practical constraints of supporting deployment and the need to reflect these constraints in increasingly faithful simulations. We describe the implementation of a set of tools and libraries that embody these principles and which are used to support the structured approach. In the final part of the thesis we discuss how the technical and environmental interdependencies as well as the design of the supporting middleware impact upon results. With reference to our results we show how the evaluation of PSN protocol performance must consider more than the tradeoffs between delivery ratio, latency and overhead. We reflect upon our use of our structured approach and how effective it is in tackling the problems that we highlight, We also argue that the performance results presented in current studies of PSN protocols and PSN networks will often be over optimistic given the constraints that emerge from deployment.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:575361 |
| Date | January 2012 |
| Creators | Lodge, Tom |
| Publisher | University of Nottingham |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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