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Effects of Routing Computations in Content-Based Routing Networks with Mobile Data Sources

This study explores the impact of routing computations on content-based routing networks with mobile data sources, such as blogs, wikis, and location-based services. It analyzes the effects of publisher mobility on protocols and proposes new protocols to handle temporary disconnections. The study also evaluates the effects of routing computations on the network.

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Effects of Routing Computations in Content-Based Routing Networks with Mobile Data Sources

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  1. Effects of Routing Computations in Content-Based Routing Networks with Mobile Data Sources Vinod Muthusamy, Milenko Petrovic, Hans-Arno Jacobsen University of Toronto August 30, 2005 Eleventh Annual International Conference on Mobile Computing and Networking (MobiCom 2005)

  2. Motivation • Explosion in the number information producers • Blogs, wikis, podcasting, photo sharing • Mobility of users • Cell phones, PDAs, sensors • Mobile information producers • Fixed information producers are increasingly mobile • New types of information producers • SMS, camera phones, location-based services • Publish/subscribe data dissemination • Well suited to mobile clients • Decoupling, filtering • Effects of routing computations on pub/sub network with mobile information producers has not been studied • Causes drastically different results and different conclusions Mobile-ToPSS (University of Toronto)

  3. Publisher Mobility Scenarios • Journalists with blogs • Update blogs on location • Upload pictures from camera phone • Police patrol car • Status reports about accidents, traffic, crime • Mail delivery • Track delivery status, location, broken parts 1 2 Information producer Mobile-ToPSS (University of Toronto)

  4. Agenda • Publish/subscribe background • Model and distributed protocol • Routing operations • Publisher mobility • Problem • Invalid assumptions cause excessive state maintenance • Solution • New protocols to distinguish temporary disconnections • Evaluation • Effects of routing computations on protocols Mobile-ToPSS (University of Toronto)

  5. Notification Notification Publish/Subscribe Model Traffic Reports Publisher Publisher Congestion Publications Gridlock Snow Need Backup Fire Accident Robbery BrokerNetwork Subscriptions Subscriber Subscriber Subscription: Name = “Bob” Report = “Accident” Subscription: Injury = True Location = “Cologne” Mobile-ToPSS (University of Toronto)

  6. Subscriber Subscriber Publisher Distributed Publish/Subscribe . . . . . . • Advertisements flooded • Create ad tree • Subscriptions along reverse ad path • Create multicast tree • Publications along reverse sub path Advertisements Subscriptions Publications Mobile-ToPSS (University of Toronto)

  7. Generic Pub/Sub Router Operations • Advertisement handling • Insert ad into AdsTable • Find covering ads • Find intersecting subs • Subscription handling • Insert sub into SubsTable • Find covering subs • Find intersecting ads • Publication handling • Find matching subs Insertion e.g. “severity < 4” Covering Y “severity < 4”is covered by“severity < 6” N Intersection N “severity < 4”intersects“severity > 2” Y Mobile-ToPSS (University of Toronto)

  8. Modeling Routing Computations • Cannot ignore computations in distributed pub/sub protocols • Classes of algorithms • FAST: tuple-based data (e.g., attribute-value pairs) • [Fabret et al., SIGMOD 2001] • COMPLEX: tree or graph structured data (e.g., XML, RDF) • [Petrovic et al., WWW 2005] • Based on best reported results under most favorable workloads *Conservative estimates where no data available(Algorithms usually tuned for matching performance) Mobile-ToPSS (University of Toronto)

  9. Publisher Mobility Mobile-ToPSS (University of Toronto)

  10. t1 t3 t4 t5 At Old Broker Disconnected At New Broker t2 Disconnect Connect Can publish (moveout) (movein) new events Publisher Mobility Problem . . . . . . • Ad and sub trees • Moveout: both trees torn down • Movein: both trees rebuilt • Expensive • # ad messages > # sub messages • No delivery until tree constructed • Distinguish temporary disconnections 1 2 moveout Publisher Mobile-ToPSS (University of Toronto)

  11. t1 t3 t4 t5 At Old Broker Disconnected At New Broker t2 Disconnect Connect Can publish (moveout) (movein) new events Publisher Mobility Problem . . . . . . • Ad and sub trees • Moveout: both trees torn down • Movein: both trees rebuilt • Expensive • # ad messages > # sub messages • No delivery until tree constructed • Distinguish temporary disconnections 1 2 movein Publisher Mobile-ToPSS (University of Toronto)

  12. t1 t3 t4 t5 At Old Broker Disconnected At New Broker t2 Disconnect Connect Can publish (moveout) (movein) new events Prefetching Protocol . . . . . . • Exploits knowledge of future mobility patterns • Concurrent • Construction at new broker • Teardown at old broker • Tree construction time hidden from user 1 2 moveout Publisher Mobile-ToPSS (University of Toronto)

  13. t1 t3 t4 t5 At Old Broker Disconnected At New Broker t2 Disconnect Connect Can publish (moveout) (movein) new events Prefetching Protocol . . . . . . • Exploits knowledge of future mobility patterns • Concurrent • Construction at new broker • Teardown at old broker • Tree construction time hidden from user 1 2 movein Publisher Mobile-ToPSS (University of Toronto)

  14. t1 t3 t4 t5 At Old Broker Disconnected At New Broker t2 Disconnect Connect Can publish (moveout) (movein) new events Proxy Protocol . . . . . . • Maintain trees from several brokers • Advantageous if restricted mobility region 1 2 moveout movein Publisher Publisher Mobile-ToPSS (University of Toronto)

  15. t1 t3 t4 t5 At Old Broker Disconnected At New Broker t2 Disconnect Connect Can publish (moveout) (movein) new events Delayed Protocol . . . . . . • Maintain trees at old broker for some time • Allow new tree to graft onto old tree • Remove extraneous portions of old tree 1 2 moveout movein Publisher Publisher Mobile-ToPSS (University of Toronto)

  16. t1 t3 t4 t5 At Old Broker Disconnected At New Broker t2 Disconnect Connect Can publish (moveout) (movein) new events Prefetch-Delayed Protocol . . . . . . • Combine advantages of • Prefetching • Tree construction time hidden from user • Delayed • Cheap tree construction cost 1 2 moveout movein Publisher Publisher Mobile-ToPSS (University of Toronto)

  17. Evaluation Mobile-ToPSS (University of Toronto)

  18. Evaluation Setup • Simulation Environment • ns-2 network simulator • Implemented mobility protocol optimizations • Parameters • Topology • Metropolitan Area Network • 4 levels of degree 4  64 leaf brokers • Subscribers: 500 • Publishers: 50 • Mobility • Static subscribers, mobile publishers • Random speeds (5km/h, 50km/h, 100km/h) • Metrics • Tree rebuild load • Tree rebuild time • • • • • • 1 64 Mobile-ToPSS (University of Toronto)

  19. Routing Computation Model • Based on conservative estimates or best published results of four pub/sub router operations • For COMPLEX: assume n = 100 000 subscriptions at each broker • Ignore other processing delay sources • Network protocol stack, operating system, etc. n = number of subscriptions Mobile-ToPSS (University of Toronto)

  20. Publisher Scalability – No Routing Computations • Standard is much worse than Proxy which is worse than Delayed, Prefetch-Delayed • For both tree reconstruction message load and time • Tree reconstruction time seems independent of number of publishers • Incorrect conclusion No algorithm No algorithm Mobile-ToPSS (University of Toronto)

  21. Publisher Scalability – With RC • With FAST algorithm • Scale: approx. 5X worse • Trend: varies with number of publishers (no longer independent) • With COMPLEX algorithm • Standard protocol collapses after 150 publishers • 60s tree rebuilding time with 250 publishers! • Routing computations can alter the apparent scalability of protocols • Network is not necessarily the bottleneck FAST algorithm COMPLEX algorithm Mobile-ToPSS (University of Toronto)

  22. Implications of Slow Tree Rebuilding • Publications sent during tree rebuilding may not be delivered • 100% delivery with no routing computation • False impression of protocol’s performance STANDARD protocol Mobile-ToPSS (University of Toronto)

  23. Proxy Locality – With RC • No change in the trends • Change in point where Proxy outperforms Prefetch-Delayed • The relative negative impact of overshoot on Proxy increases with more expressive subscription languages No algorithm FAST algorithm COMPLEX algorithm Mobile-ToPSS (University of Toronto)

  24. Conclusions • The publish/subscribe model is well suited to mobile applications • No evaluation of mobility with routing computations • Routing computations cannot be ignored in pub/sub protocols • Not a lower order effect • Affect the scale, trend, tradeoff points of results • Alter the conclusions of protocols’ performance • Future Work • Refine computation models • Expect greater impact of routing computations • Other scenarios: realistic traces, mobile subscribers Mobile-ToPSS (University of Toronto)

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