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RUBI Adaptive Resource Discovery for Ubiquitous Computing Rae Harbird [email protected] MPAC 2004 Stephen Hailes [email protected] Rae Harbird Cecilia Mascolo [email protected] 1 RUBI • Resource discovery for Ubiquitous computing • Autonomic, encapsulating overarching adaptive process • Few assumptions are made about the network environment • Operational over a wide range of network conditions MPAC 2004 Rae Harbird 2 Outline • Ubiquitous computing and resource discovery • Review of existing protocols • RUBI, design and evaluation • Future work • Conclusions and questions MPAC 2004 Rae Harbird 3 Ubiquitous Computing • Weiser’s vision becoming reality – 250 million microprocessors sold monthly, < 2 % destined for PCs • Ubicomp revenue – Provision of novel services, low / no ROI from connectivity alone • Environmental implications – Huge heterogeneity, immense scale, dynamic operation and volatility MPAC 2004 Rae Harbird 4 Communications Paradigm MPAC 2004 Rae Harbird 5 Communications Paradigm MPAC 2004 Rae Harbird 6 Previous Work • Global, central index of resources – Jini • Global, distributed index – Distributed hash tables • Resources discovered as needed – Konark, UPnP, SLP • Resource discovery based on ad hoc routing protocols MPAC 2004 Rae Harbird 7 Proactive Resource Advertisement MPAC 2004 Rae Harbird 8 Proactive Resource Advertisement MPAC 2004 Rae Harbird 9 Proactive Resource Advertisement MPAC 2004 Rae Harbird 10 Requests & Replies MPAC 2004 Rae Harbird 11 Reactive Resource Requests & Replies MPAC 2004 Rae Harbird 12 Reactive Resource Requests & Replies MPAC 2004 Rae Harbird 13 Reactive Resource Requests & Replies MPAC 2004 Rae Harbird 14 Reactive Resource Requests & Replies MPAC 2004 Rae Harbird 15 Varying level of node mobility MPAC 2004 Rae Harbird 16 RUBI • RUBI based on two routing algorithms: – proactive (OLSR) and reactive (AODV) • Assumptions: – IP level connectivity over any type of wireless link – Assume nodes can create or obtain an IP address – Operates at the network layer or at the application layer MPAC 2004 Rae Harbird 17 Algorithm Selection • How does a node determine the type of region it belongs to? • Link duration is used as a mobility feedback mechanism • Neighbour establishment used to assess stability of local links • Select routing algorithm based on perceived stability – Proactive algorithm: stable enough to elect relay nodes – Reactive algorithm: in all other cases MPAC 2004 Rae Harbird 18 Proactive Request to Reactive Region MPAC 2004 Rae Harbird 19 Proactive Request to Reactive Region MPAC 2004 Rae Harbird 20 Response Implosion • Problem: – A large number of replies may be returned to the source of the query • Solutions: – Introduce delay for nodes on the reply path • Wait for a period and evaluate replies received before sending one onwards • Evaluation can be difficult – Use request cancellation message from source when reply received MPAC 2004 Rae Harbird 21 Ensure Loop Free Operation • Problem – For composite requests, a node may satisfy only part of it – Will forward a request for remaining (unfulfilled) resources – Must ensure that new request is not processed by nodes that have already seen it • Solution – Preserve original message ID MPAC 2004 Rae Harbird 22 Experiment Design • Choose simple scenarios to test different aspects of protocol behaviour • Fixed characteristics • Network size, density • Relative node mobility • Mobility model • Node: Bandwidth, Power, Speed • Varying characteristics • Cache size and caching period • Request rate MPAC 2004 Rae Harbird 23 Measuring Performance • Request success rate • Protocol message overhead per resource request • Latency of replies – Showing where congestion exists in the network • Amount of state maintained per node • Request path length – Number of hops a query must traverse in order to obtain a response MPAC 2004 Rae Harbird 24 Discussion • RUBI represents trade-off between: – Context-aware operation – Efficiencies gained by assuming stability • Greater overhead than some approaches reviewed – Neighbour establishment and monitoring • More suitable for ubiquitous computing – Adaptive in an uncertain network environment MPAC 2004 Rae Harbird 25 Conclusions • Resource discovery – Key factor in realisation of ubicomp vision • RUBI designed with ubicomp environment in mind – Routing algorithms ensure the efficient dissemination of information – Autonomously adapts using locally obtained information – More suitable than other ‘single algorithm’ approaches MPAC 2004 Rae Harbird 26