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Imre Kelényi Budapest University of Technology and Economics

Optimizing Energy Consumption of Mobile Nodes in Heterogeneous Kademlia-based Distributed Hash Tables. Imre Kelényi Budapest University of Technology and Economics Department of Automation and Applied Informatics Jukka K. Nurminen Nokia Research Center. Agenda.

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Imre Kelényi Budapest University of Technology and Economics

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  1. Optimizing Energy Consumption of Mobile Nodes in Heterogeneous Kademlia-based Distributed Hash Tables Imre Kelényi Budapest University of Technology and Economics Department of Automation and Applied Informatics Jukka K. Nurminen Nokia Research Center NGMAST 2008 - Mobile DHT Energy

  2. Agenda • Distributed Hash Tables (DHT) • DHT on mobile phones • Probabilistic message dropping • Measurements and results • Analytical model • Conclusion NGMAST 2008 - Mobile DHT Energy

  3. Distributed Hash Tables (DHT) • Peer-to-peer systems that enable the storage and retrieval of <key,value> pairs in a completely distributed and scalable way • Distributed storage systems, file sharing, service discovery, P2P SIP, etc. • DHT nodes communicate with each other via messages (e.g. over UDP datagramms) • There has not been any mobile implementation NGMAST 2008 - Mobile DHT Energy

  4. DHT on mobile phones • Mobile Kademlia for Symbian OS • Implements the Kademlia DHT protocol • It can connect to the global Mainline BitTorrent DHT network (usually has more than 1 million concurrent users) • Opensource project • More information:http://www.aut.bme.hu/MobileDHT NGMAST 2008 - Mobile DHT Energy

  5. Problem with the mobile DHT • When connected to a large DHT, the energy consumption is so highthat the battery is depleted in a couple of hours • This is mostly the result of thelarge incoming traffic: requests coming from other DHT nodes NGMAST 2008 - Mobile DHT Energy

  6. First solution: block all requests • It is possible to block all incoming requests and thus operate in client-only mode • Significant energy conservation but also decreases DHT performance NGMAST 2008 - Mobile DHT Energy

  7. Probabilistic message dropping • Concept: do not block all incoming requests but a fraction of them • Energy is conserved • The node still participates in the DHT to some degree • Implementation: if an incoming request is received, it isdropped with a certain probability Pdrop • The largerPdropis, the more messages are blocked and more energy is conserved • Fullpeer: Pdrop=0, client-only: Pdrop=1 • It does not require any protocol modifications in the other nodes (backward compatible)! NGMAST 2008 - Mobile DHT Energy

  8. Probabilistic message dropping • Protocol requirement • The DHT must store multiple replicas of the stored values • Energy is conserved • Responsesarenotsent out • Less requests are received NGMAST 2008 - Mobile DHT Energy

  9. Measurement results • Performed with a Nokia N95, connected to the Mainline BitTorrent DHT • Average of 3-hour-long sessions NGMAST 2008 - Mobile DHT Energy

  10. Message traffic statistics NGMAST 2008 - Mobile DHT Energy

  11. Analytical Model on DHT Performance • Increasing Pdrop decreases the performance of the DHT, but to what extent? • Our analytical modelcharacterizes the lookup latency of the DHT as a function of Pdrop and the ratio of mobile nodes in the network m NGMAST 2008 - Mobile DHT Energy

  12. Analytical Model on DHT Performance • Expected lookup latency in Mainline BitTorrent DHT as a function of m(ratio of mobiles) and Pdrop NGMAST 2008 - Mobile DHT Energy

  13. Conclusion • Probabilistic message dropping enables heterogeneity in DHTs without protocol modification • It enables mobile nodes with scarce resources, most importantly battery capacity, to join DHTs • Finding the optimal value for Pdrop is still an open question • Dynamical adjusting NGMAST 2008 - Mobile DHT Energy

  14. Thank You! • More information: • http://www.aut.bme.hu/mobiledht • http://amorg.aut.bme.hu • Questions? NGMAST 2008 - Mobile DHT Energy

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