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EcoRep: An Economic Incentive Model for Mobile-P2P networks. Anirban Mondal (University of Tokyo, JAPAN) Sanjay K. Madria (University of Missouri-Rolla, USA) Masaru Kitsuregawa (University of Tokyo, JAPAN). Contact Email address: anirban@tkl.iis.u-tokyo.ac.jp. INTRODUCTION.
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EcoRep: An Economic Incentive Model for Mobile-P2P networks Anirban Mondal (University of Tokyo, JAPAN) Sanjay K. Madria (University of Missouri-Rolla, USA) Masaru Kitsuregawa (University of Tokyo, JAPAN) Contact Email address: anirban@tkl.iis.u-tokyo.ac.jp
INTRODUCTION Ever-increasing popularity and proliferation of mobile technology Mobile user statistics for JAPAN Jan 31, 2006 (http://www.wirelesswatch.jp/)
Proliferation of mobile devices M-P2P Paradigm
Proliferation of mobile devices + Popularity of the P2P paradigm e.g., Kazaa M-P2P Paradigm
Proliferation of mobile devices + Popularity of the P2P paradigm e.g., Kazaa M-P2P Paradigm
Proliferation of mobile devices + Popularity of the P2P paradigm e.g., Kazaa M-P2P Paradigm • M-P2P network: Mobile Hosts (MHs) interact in a P2P fashion • Sometimes, base station infrastructure does not exist • Current infrastructures are beginning to support P2P interactions among mobile devices e.g., Microsoft’s Zune
M-P2P APPLICATION SCENARIOS Find the cheapest Levis Jeans in a shopping district
M-P2P APPLICATION SCENARIOS Find the cheapest steak restaurant nearby me
M-P2P APPLICATION SCENARIOS Which museum room do I visit next?
M-P2P APPLICATION SCENARIOS What are the traffic conditions a few miles ahead?
Challenges in M-P2P networks Low data availability • frequent network partitioning due to mobility
Challenges in M-P2P networks Dynamic data replication Low data availability • frequent network partitioning due to mobility
Challenges in M-P2P networks Dynamic data replication Low data availability • frequent network partitioning due to mobility Free-riding (limited resources of MHs)
Challenges in M-P2P networks Dynamic data replication Low data availability • frequent network partitioning due to mobility Free-riding (limited resources of MHs) Economic Incentive model
Challenges in M-P2P networks Dynamic data replication Low data availability • frequent network partitioning due to mobility Free-riding (limited resources of MHs) Economic Incentive model This motivates us to investigate an economic incentive model for dynamic replication in Mobile-P2P networks.
Main contributions • An economic model for M-P2P networks • A query issuing mobile peer pays the price of the service to the query serving mobile peer • Virtual currency model • Discourages free-riding • Fairness in replica allocation • by considering the origin of queries for data items
Related Works • Economic models have been discussed primarily for resource allocation in distributed systems. • They do not address fairness in replica allocation and P2P concerns such as free-riding. • They do not address M-P2P issues such as frequent network partitioning and mobile resource constraints. • [Ouri:04] has proposed an M-P2P economic model • [Ouri:04] aims at data dissemination, while we consider on-demand services. • [Ouri:04] does not consider replication. • Works on free-riding discuss utility functions to capture user contributions and trust issues • These works are completely orthogonal to replication issues associated with free-riding. • Existing P2P replication protocols are not adequate for M-P2P due to mobility issues. • [Hara:05] presents M-P2P replica allocation methods with periodic and aperiodic updates • [Hara:05] does not consider economic issues, load sharing and tolerance to weaker consistency.
ARCHITECTURE OF EcoRep • EcoRep considers a hybrid super-peer architecture • some of the MHs act as the ‘Super-peers’ (SPs). • SPs have high processing capacity, high available bandwidth and high energy. • Neighbouring SPs periodically exchange their regional information concerning MH characteristics (e.g., load, energy) to facilitate replication. • In case of SP failures, neighbouring GNs could take over the responsibility of the failed GN. • SPs can also collaborate for search and replication across different regions.
QUERY PROCESSING IN EcoRep • When an MH enters a region R, it registers with the SP S in R. • S provides the MH with the list of data items currently available in R. • EachMH periodicallysends its list of data items and replicas to its corresponding SP. • SP periodically broadcasts the list of available items within its region to the MHs in its region. • A query issuing MH M can distinguish whether its query is local or global. • EcoRep supports both local and remotequerying. • Local queries: Broadcast mechanism (need not pass via SP) • Remote queries: SP forwards query to its neighbouring SPs.
Core idea • Services • providing data • providing computational power e.g., convert to PDF • message relay services • Every service has a price • Service-requestor pays the price of the service to the service-provider. • Revenue of an MH is how much currency it has • MH spends currency on obtaining services • MH earns currency by providing services
Computation of data item price • Price of data item d depends on • access frequency
Computation of data item price • Price of data item d depends on • access frequency • number of MHs served by d (fairness issue)
Computation of data item price • Price of data item d depends on • access frequency • number of MHs served by d (fairness issue) • number of existing replicas of d
Computation of data item price • Price of data item d depends on • access frequency • number of MHs served by d (fairness issue) • number of existing replicas of d • (replica) consistency of d
Computation of data item price • Price of data item d depends on • access frequency • number of MHs served by d (fairness issue) • number of existing replicas of d • (replica) consistency of d • average response time for queries on d
Computation of data item price • Price of data item d depends on • access frequency • number of MHs served by d (fairness issue) • number of existing replicas of d • (replica) consistency of d • average response time for queries on d
Interaction between revenue and load • MH M could have high revenue but low load due to • serving only a few requests for some high-priced data items, but not issuing any queries • M could have low revenue but high load due to • serving a large number of access requests for low-priced data items • Even if M earns high amounts of virtual currency, M’s revenue could still be low if M issues several queries for high-priced data items.
Interaction between revenue and load • MH M could have high revenue but low load due to • serving only a few requests for some high-priced data items, but not issuing any queries • M could have low revenue but high load due to • serving a large number of access requests for low-priced data items • Even if M earns high amounts of virtual currency, M’s revenue could still be low if M issues several queries for high-priced data items. There is no direct correlation between the revenue and load of an MH.
Revenue and Load in EcoRep • We use a parameter ג that can be tweaked to adjust the relative importance of revenue and load during replica allocation. • We use normalized values of revenue and load to correctly reflect the relative weights of revenue and load. • We consider three cases: • Revenue and load are both assigned equal weights: ג = R + L • Revenue is assigned higher weight than load: ג = 2R + L • Revenue is assigned lower weight than load: ג = R + 2L
EcoRep replica allocation • Each SP performs replica allocation within the region that it covers. • Periodically, each MH sends to its SP • current (x,y) coordinates • revenue value • the prices of items stored at itself • load • energy • available memory space status • SP collates the (x,y) coordinate information of all the MHs in its region to estimate the network topology during the time of replica allocation. • The algorithms provide revenue and load-balance • Revenue-balance avoids starvation of MHs and encourages MH participation in the network • Load-balance reduces query response times
EcoRep Replica Allocation (CONT.) • Key idea: Assign higher-priced data items to MHs with either low revenue or low load (spectrum of algorithms with different weights for revenue and load). • Replica allocation criteria • Revenue • Load • k-hop neighbours of MH which access the data max number of times • Available memory space • Probability of MH availability • Query redirection to replicas is based on • Revenue • Load • Probability of MH availability
Replica allocation algorithm Higher-priced data items are given preference
Replica allocation algorithm { Bringing the data nearer to the origin of most of the requests for the data
Replica allocation algorithm { Consideration of memory space, energy, load and probability of availability of MHs
Replica allocation algorithm Revenue-balance and load-balance
Replica allocation algorithm Recomputing the price of data items after replica allocation as price depends upon no. of existing replicas
Performance Study • Metrics • Average Response time ART • Data Availability • Traffic (hop-count) during replica allocation
Practical deployment issues • What should be the exchange rate between virtual money and real money? • 1000 units of virtual currency = ? Yen • How to ensure collection of payments? • Escrow method?? • Should real money be used? • High cost of micro-economic transactions • Virtual money should work as long as it is of value to M-P2P users • Example: MTV could give Bob 50 units of virtual money if he agrees to stream a video-clip in a busy market-place 25 times on a Sunday. Bob could buy some MTV products using the 50 units he obtains.
SUMMARY • A mobile peer needs incentives to provide services to other mobile peers • Incentives are likely to improve participation of mobile peers higher available bandwidth, larger pool of memory space, multiple paths to answer a query etc • Our works aim at enticing non-cooperative peers to provide service in M-P2P networks