A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 1
A Distributed Search Service for P2P A Distributed Search Service for P2P File Sharing in Mobile ApplicationsFile Sharing in Mobile Applications
4 September, 20034 September, 2003
Authors - Christoph Lindemann and Oliver P. Waldhorst, University of Dormund, Dept. of Computer ScienceAuthors - Christoph Lindemann and Oliver P. Waldhorst, University of Dormund, Dept. of Computer Science
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 22
ItineraryItinerary
Background StudiesBackground Studies
Introducing Passive Distributed Indexing (PDI)Introducing Passive Distributed Indexing (PDI)
Algorithm DetailsAlgorithm Details
Performance ResultsPerformance Results
Conclusion and Future WorkConclusion and Future Work
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 33
Background StudiesBackground StudiesA Mobile Ac-Hoc Network
Short-range Wireless, e.g. Bluetooth
Medium-range Wireless, e.g. IEEE 802.11
Such Ac-Hoc Network can be used for data sharing between mobiles,e.g. Documents, MP3s and Video Clips
How to enable searching of P2P data on top of the architecture?
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 44
Background StudiesBackground StudiesRelated Works
SolutionsSolutions CommentsComments
NapsterNapsterHybid P2P using a CenHybid P2P using a Centralized Index Servertralized Index Server
No mobile device in general has the capability to act No mobile device in general has the capability to act as the central serveras the central server
Even there is a central server, it cannot be Even there is a central server, it cannot be reachable from all client due to Hidden-Node reachable from all client due to Hidden-Node ProblemProblem
GnutellaGnutellaFully distributed Fully distributed searching using multi-searching using multi-hop flood algorithmhop flood algorithm
Flooding entire network with query messages limits Flooding entire network with query messages limits its scalabilityits scalability
7DS7DSFirst in mobile First in mobile environment, utilizing environment, utilizing flood algorithmflood algorithm
Similar drawback as GnutellaSimilar drawback as Gnutella
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 55
Proposed SolutionProposed SolutionObjectivesObjectives
“to provide a general-purpose file search service which can “to provide a general-purpose file search service which can be used by several kinds of mobile applications running on top”be used by several kinds of mobile applications running on top”
Passive Distributed Indexing (PDI) Passive Distributed Indexing (PDI)
- Each device stores its local documents as a - Each device stores its local documents as a RepositoryRepository
- Uniquely identify documents with its local path- Uniquely identify documents with its local pathand unique device ID, a.k.a. and unique device ID, a.k.a. Document IdentifierDocument Identifier
- A local - A local Index CacheIndex Cache is maintained on each device, is maintained on each device,which forms the core component of this architecturewhich forms the core component of this architecture
- Searching is performed by keyword searches- Searching is performed by keyword searches
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 66
Passive Distributed IndexingPassive Distributed IndexingOperation Scenario
Node 1
Node 2
Node 3
…
q: d1, d2
q: d2, d3
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 77
Passive Distributed IndexingPassive Distributed IndexingOperation Scenario
Node 1
Node 2
Node 3
[QUE]
q ?…
q: d1, d2
q: d2, d3
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 88
Passive Distributed IndexingPassive Distributed IndexingOperation Scenario
Node 1
Node 2
Node 3
…
q: d1, d2
q: d2, d3
[QUE]
q ?
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 99
Passive Distributed IndexingPassive Distributed IndexingOperation Scenario
Node 1
Node 2
Node 3
q: d1, d2
q: d1, d2, d3
q: d1, d2, d3
[REP]
q : d1, d2
[REP]
q : d2, d3[REP]
q : d1, d2
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 1010
Passive Distributed IndexingPassive Distributed IndexingOperation Scenario
Node 1
Node 2
Node 3
q: d1, d2, d3
q: d1, d2, d3
q: d1, d2, d3
[REP]
q : d3
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 1111
Performance AnalysisPerformance AnalysisIndependent Parameters
No. of Devices,
Transmission Range,
Mobility Model
No. of Documents,
No. of Keywordsof Interest,
Distribution of Keywords
Inter-request Timeof Queries
Index Cache Size,
Max. TTL,
(Document Timeout)
System Param.System Param. Application Param.Application Param. Protocol Param.Protocol Param.
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 1212
Performance AnalysisPerformance AnalysisValues for Simulation
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 1313
Performance AnalysisPerformance AnalysisPerformance Measure
?
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 1414
Performance AnalysisPerformance AnalysisPerformance Measure
?
Nall = 5
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 1515
Performance AnalysisPerformance AnalysisPerformance Measure
?
Nall = 5 Nrep = 3
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 1616
Performance AnalysisPerformance AnalysisPerformance Measure
?
Nall = 5 Nrep = 3
Query Hit Rate = Nrep / Nall
(other performance measures, e.g. system response time, is left for future work.)
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 1717
Analysis of ResultsAnalysis of ResultsSensitivity to System Parameters : No. of Devices & Index Cache Size
Local Index Local Index Cache has Cache has very little very little ImpactImpact
Limited impact Limited impact of of ↑in No. of ↑in No. of devices on devices on PDI PDI performance performance (1)(1)
↑↑in No. of in No. of devices leads devices leads to to ↑in↑in PDI PDI performance performance (2)(2)
(1, 2) Small index cache cannot accommodate entries for all matching documents
Conclusion : Index Cache size can be small when No. of devices is small, whereas sufficient index cache size can boost performance in case of large No. of devices
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 1818
Analysis of ResultsAnalysis of ResultsSensitivity to System Parameters : No. of Devices & Forwarding TTL
Message Message forwarding has forwarding has very little very little ImpactImpact
Forwarding Forwarding improves improves performance performance by 20% by 20% (1)(1)
(1) A higher probability of reaching more devices for forwarding in medium No. of devices
(2) High No. of devices fills local index cache with nearby entries, which replaces message-forwarding adequately
Conclusion : Forwarding is useful in medium density systems, but should be disabled for high density systems to avoid unnecessary network traffic
Advantage Advantage vanished vanished when No. of when No. of devices grows devices grows further further (2)(2)
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 1919
Analysis of ResultsAnalysis of ResultsSensitivity to System Parameters : Transmission Range & Index Cache Size
Local Index Local Index Cache has Cache has very little very little ImpactImpact (1) (1)
Index Cache Index Cache Size Size significantly significantly improves improves performanceperformance
(1) Small No. of devices is reached with very low transmission range, thus increase in cache size makes no impact
Conclusion : Index Cache size can be small for short-range devices such as Bluetooth, whereas No. of devices should be high to compensate for the low Hit Rate
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 2020
Analysis of ResultsAnalysis of ResultsSensitivity to System Parameters : Transmission Range & Forwarding TTL
PDI with PDI with message message forwarding forwarding disabled gains disabled gains best best performance performance for high-range for high-range devicesdevices
(1) Responses for uncommon entries are still forwarded over great distances, that fills index caches with junk entries
Conclusion : When transmission range is high, message forwarding should be disabled
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 2121
Analysis of ResultsAnalysis of ResultsSensitivity to App Parameters : Zipf
Zipf-like distribution is used to model PDF of searching keywords
For keyword kj,
Pr(k = kj) ≈ j- α ,
for 0 <= α <= 1
Therefore, the higher the α, more localized is the query stream
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 2222
Analysis of ResultsAnalysis of ResultsSensitivity to App Parameters : Zipf & Index Cache Size
PDI is PDI is extremely extremely sensitivity to sensitivity to locality in locality in request request stream for stream for small Index small Index CacheCache
Conclusion : For applications offering no significant locality in the request stream, sizes of Index Cache must be chosen adequate
PDI can PDI can achieve a hit achieve a hit rate of > 70% rate of > 70% despite of despite of locality in large locality in large Index CacheIndex Cache
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 2323
Analysis of ResultsAnalysis of ResultsSensitivity to App Parameters : Zipf & Forwarding TTL
PDI is gains PDI is gains performance performance improvements improvements from packet from packet forwarding for forwarding for higher locality, higher locality, 2-hop 2-hop forwarding forwarding performs performs similarly with similarly with higher Hopshigher Hops
Conclusion : 2-hop message forwarding should be enabled in applications offering a high degree of locality in request stream
For even For even higher locality, higher locality, 2-hop 2-hop forwarding forwarding out-performs out-performs the othersthe others
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 2424
Analysis of ResultsAnalysis of ResultsSensitivity to App Parameters : No. of Document & Index Cache Size
Performance Performance decreases decreases linearly with linearly with No. of No. of documents per documents per devicedevice
(1) Has been shown elsewhere what this behaviors is explained if a Zipf-like request distribution is assumed
Conclusion : Maybe more sophisticated Forwarding Strategies rather than increasing Index Cache Size should be employed to improve the performance
Performance Performance increases with increases with Index Cache Index Cache size in only a size in only a log-like log-like fashion fashion (1)(1)
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 2525
Analysis of ResultsAnalysis of ResultsSensitivity to App Parameters : No. of Document & Index Cache Size
Performance Performance is improved by is improved by 10% if a small 10% if a small No. of No. of documents documents exists in each exists in each device, with device, with near-maximal near-maximal performance performance with 2-hop with 2-hop forwardingforwarding
Conclusion : 2-hop forwarding can improves performance in small No. of documents per device, but all forwarding gains no performance when No. of documents per device is large
For large No. For large No. of documents of documents per device, no per device, no significant significant difference in difference in forwarding forwarding strategystrategy
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 2626
Analysis of ResultsAnalysis of ResultsTransient Behaviors
Real Hit Rate Real Hit Rate is constant is constant over timeover time
Real Hit Rate : Rate of hits reported from devices actually hold a matching document
Conclusion : System will attain its maximal performance automatically and no initial warm-up mechanism is required
PDI Hit Rate PDI Hit Rate increases increases steadily after steadily after simulation simulation startstart
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 2727
Conclusion and Future WorkConclusion and Future Work
General-purpose Distributed Document Search Service
Utilizes Local Caching of Query Results to Avoid Flooding the Network
Tunable(Cache Size, TTL, Document Timeout)
to Support Different Environments & Applications
PDI is …
Provides an Initial Filling of Index Caches in a Very Short Time, No Warm-up Mechanism is Needed
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 2828
Requires Sufficiently Large Index Cache Size
2-hop Packet Forwarding should be DisabledIf Either
The No. of Devices or Transmission Range is High
Requires Sufficient Large Index Cache Size
Conclusion and Future WorkConclusion and Future Work
Contributions of Simulation Results
High Density,Low Query Locality
Medium Density, Medium-range
Large No. ofDocuments
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 2929
Conclusion and Future WorkConclusion and Future Work
Future Works include …
1. Investigation on the Impact of Document Modifications on the Performance of PDI, and the Design of the Appropriate Workaround Mechanism
2. Evaluation of the Performance of PDI considering Sophisticated Workload Models that Contains Location Depended Queries
3. Development of a Prototype Implementation of PDI and Field Tests
A Distributed Search Service for Peer-to-Peer File Sharing in Mobile ApplicationA Distributed Search Service for Peer-to-Peer File Sharing in Mobile Application Presented by Tony Sung On Loy, MC Lab, CUHK IEPresented by Tony Sung On Loy, MC Lab, CUHK IE 3030
Conclusion and Future WorkConclusion and Future Work
Comments …
1. PDI is a very simple solution for porting P2P File Sharing to Ac-Hoc Mobile Network
2. The Paper contains comprehensive simulation results and analysis of the PDI mechanism
3. However, the author did not suggest further modification on the PDI mechanism based on the analyzed results
4. There is also no analytical comparisons to any other similar implementations
5. PDI is yet to be challenged for improvement
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