1. MPAC 2004Rae Harbird 1 RUBI Adaptive Resource Discovery for Ubiquitous Computing Rae Harbird R.Harbird@cs.ucl.ac.uk Stephen Hailes S.Hailes@cs.ucl.ac.uk Cecilia Mascolo C.Mascolo@cs.ucl.ac.uk

2. MPAC 2004Rae Harbird 2 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

3. MPAC 2004Rae Harbird 3 Outline Ubiquitous computing and resource discovery Review of existing protocols RUBI, design and evaluation Future work Conclusions and questions

4. MPAC 2004Rae Harbird 4 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

5. MPAC 2004Rae Harbird 5 Communications Paradigm

6. MPAC 2004Rae Harbird 6 Communications Paradigm

7. MPAC 2004Rae Harbird 7 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

8. MPAC 2004Rae Harbird 8 Proactive Resource Advertisement

9. MPAC 2004Rae Harbird 9 Proactive Resource Advertisement

10. MPAC 2004Rae Harbird 10 Proactive Resource Advertisement

11. MPAC 2004Rae Harbird 11 Requests & Replies

12. MPAC 2004Rae Harbird 12 Reactive Resource Requests & Replies

13. MPAC 2004Rae Harbird 13 Reactive Resource Requests & Replies

14. MPAC 2004Rae Harbird 14 Reactive Resource Requests & Replies

15. MPAC 2004Rae Harbird 15 Reactive Resource Requests & Replies

16. MPAC 2004Rae Harbird 16 Varying level of node mobility

17. MPAC 2004Rae Harbird 17 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

18. MPAC 2004Rae Harbird 18 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

19. MPAC 2004Rae Harbird 19 Proactive Request to Reactive Region

20. MPAC 2004Rae Harbird 20 Proactive Request to Reactive Region

21. MPAC 2004Rae Harbird 21 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

22. MPAC 2004Rae Harbird 22 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

23. MPAC 2004Rae Harbird 23 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

24. MPAC 2004Rae Harbird 24 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

25. MPAC 2004Rae Harbird 25 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

26. MPAC 2004Rae Harbird 26 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