Imre Kelényi Budapest University of Technology and Economics
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Transcript of Imre Kelényi Budapest University of Technology and Economics
NGMAST 2008 - Mobile DHT Energy 1
Optimizing Energy Consumption of Mobile Nodes in Heterogeneous Kademlia-based Distributed Hash Tables
Imre KelényiBudapest University of Technology and Economics
Department of Automation and Applied Informatics
Jukka K. NurminenNokia Research Center
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Agenda Distributed Hash Tables (DHT)
DHT on mobile phones
Probabilistic message dropping
Measurements and results
Analytical model
Conclusion
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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
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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)
Open source project More information:
http://www.aut.bme.hu/MobileDHT
Problem with the mobile DHT When connected to a large DHT, the energy consumption
is so high that the battery is depleted in a couple of hours
This is mostly the result of the large incoming traffic: requests coming from other DHT nodes
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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
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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 is dropped with a certain probability Pdrop
The larger Pdrop is, the more messages are blocked and more energy is conserved
Full peer: Pdrop=0, client-only: Pdrop=1
It does not require any protocol modifications in the other nodes (backward compatible)!
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Probabilistic message dropping Protocol requirement
The DHT must store multiple replicas of the stored values
Energy is conserved Responses are not sent out
Less requests are received
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Measurement results Performed with a Nokia N95, connected to
the Mainline BitTorrent DHT
Average of 3-hour-long sessions
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Message traffic statistics
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Analytical Model on DHT Performance Increasing Pdrop decreases the performance of
the DHT, but to what extent?
Our analytical model characterizes the lookup latency of the DHT as a function of Pdrop and the ratio of mobile nodes in the network m
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Analytical Model on DHT Performance Expected lookup latency in Mainline BitTorrent DHT
as a function of m (ratio of mobiles) and Pdrop
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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
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Thank You! More information:
http://www.aut.bme.hu/mobiledht
http://amorg.aut.bme.hu
Questions?
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