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)

Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 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

Aug. 30, 2005 (MobiCom ’05) 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 a ccidents, traffic, crime Mail delivery  Track delivery status, location, broken parts Information producer 12

Aug. 30, 2005 (MobiCom ’05) 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

Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 5 Publish/Subscribe Model Publisher Subscriber Subscriptions Publications Notification Gridlock Robbery Accident Need Backup Snow Fire Congestion Traffic Reports Subscription: Name = “Bob” Report = “Accident” Broker Network Subscription: Injury = True Location = “Cologne”

Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 6 Distributed Publish/Subscribe Advertisements flooded  Create ad tree Subscriptions along reverse ad path  Create multicast tree Publications along reverse sub path Publisher Subscriber...  Advertisements  Subscriptions  Publications

Aug. 30, 2005 (MobiCom ’05) 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 Covering Intersection Y Y N N e.g. “severity < 4” “severity < 4” is covered by “severity < 6” “severity 2”

Aug. 30, 2005 (MobiCom ’05) 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 OperationFASTCOMPLEX MatchingO(1)O(n) CoveringO(matching)* IntersectionO(matching)* InsertionO(matching)* *Conservative estimates where no data available (Algorithms usually tuned for matching performance)

Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 9 Publisher Mobility

Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 10 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 t1t1 At Old Broker t3t3 DisconnectedAt New Broker t5t5 t4t4 Can publish new events Connect (movein) Disconnect (moveout) t2t2 moveout Publisher 12...

Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 11 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 t1t1 At Old Broker t3t3 DisconnectedAt New Broker t5t5 t4t4 Can publish new events Connect (movein) Disconnect (moveout) t2t2 movein Publisher 12...

Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 12 Prefetching Protocol Exploits knowledge of future mobility patterns Concurrent  Construction at new broker  Teardown at old broker Tree construction time hidden from user t1t1 At Old Broker t3t3 DisconnectedAt New Broker t5t5 t4t4 Can publish new events Connect (movein) Disconnect (moveout) t2t2 moveout Publisher 12...

Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 13 Prefetching Protocol Exploits knowledge of future mobility patterns Concurrent  Construction at new broker  Teardown at old broker Tree construction time hidden from user t1t1 At Old Broker t3t3 DisconnectedAt New Broker t5t5 t4t4 Can publish new events Connect (movein) Disconnect (moveout) t2t2 movein Publisher 12...

Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 14 Proxy Protocol Maintain trees from several brokers Advantageous if restricted mobility region t1t1 At Old Broker t3t3 DisconnectedAt New Broker t5t5 t4t4 Can publish new events Connect (movein) Disconnect (moveout) t2t2 moveout Publisher movein Publisher

Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 15 Delayed Protocol Maintain trees at old broker for some time Allow new tree to graft onto old tree Remove extraneous portions of old tree t1t1 At Old Broker t3t3 DisconnectedAt New Broker t5t5 t4t4 Can publish new events Connect (movein) Disconnect (moveout) t2t2 moveout Publisher movein Publisher

Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 16 Prefetch-Delayed Protocol Combine advantages of  Prefetching Tree construction time hidden from user  Delayed Cheap tree construction cost t1t1 At Old Broker t3t3 DisconnectedAt New Broker t5t5 t4t4 Can publish new events Connect (movein) Disconnect (moveout) t2t2 moveout Publisher movein Publisher

Aug. 30, 2005 (MobiCom ’05) Mobile-ToPSS (University of Toronto) 17 Evaluation

Aug. 30, 2005 (MobiCom ’05) 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 64 1

Aug. 30, 2005 (MobiCom ’05) 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 = subscriptions at each broker Ignore other processing delay sources  Network protocol stack, operating system, etc. OperationFASTCOMPLEX Matching2 msn / ms Covering2 msn / ms Intersection2 msn / ms Insertion2 msn / ms n = number of subscriptions

Aug. 30, 2005 (MobiCom ’05) 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

Aug. 30, 2005 (MobiCom ’05) 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 algorithmCOMPLEX algorithm

Aug. 30, 2005 (MobiCom ’05) 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

Aug. 30, 2005 (MobiCom ’05) 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 algorithmFAST algorithmCOMPLEX algorithm

Aug. 30, 2005 (MobiCom ’05) 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