Resource sharing in mobile wireless networks

1. Resource sharing in mobile wireless networks Maria Papadopouli Computer Science Department Columbia University http://www.cs.columbia.edu/~maria

2. Academic background • Columbia University Ph.D. candidate Fall 1996- advisor Prof. GolubchikFall 1996–1998 advisor Prof. SchulzrinneFall 1998- • New York University M.S. Computer Science May 1994 • University of Crete B.S. Computer Science June 1992

3. References on resource sharing in mobile ad hoc networks with Prof. Schulzrinne • “Effects of power conservation, wireless coverage & cooperation on data dissemination among wireless devices “, ACM MobiHoc 2001 • “Performance analysis of 7DS a data dissemination & prefetching tool for mobile users”,IEEE Sarnoff 2001, best paper/poster award • “7DS in mobile ad hoc networks”,Globecom 2000 • “Performance of data dissemination among mobile devices”,journal submission, 2002 • “Design & implementation of a P2P data dissemination & prefetching tool for mobile users”,Metro 2001 • “Network connection sharing in ad hoc wireless network among collaborative hosts”,Nossdav 1999

4. References on video on demand with Prof. Golubchik • "A Scalable Video on Demand server for a Dynamic Heterogeneous Environment", Lecture Notes in Computer Science, Springer 1998 • "Support  of VBR Video Streams Under Disk Bandwidth Limitations", ACM SIGMETRICS Performance Evaluation Review 1997 •  (with also J.C-S. Lui), "A survey of approaches to fault tolerant design of video on demand servers: Techniques, analysis and comparison", Special issue of Parallel Computing Journalon Parallel Data Servers and Applications1998

5. Outline • Introduction • Background on wireless data access • Motivation • Overview of 7DS • Performance analysis on 7DS • Conclusions • Future work

6. Background • Fast growth in pervasive computing devices • Fast wireless data servicesgrowth • Base stations for wireless WAN will not keep pace • Regulatory, environmental & cost barriers for a dense deployment Users experience intermittent connectivity & limited data access

7. Mobile information access Dependency oninfrastructure : • Wireless WAN eg 802.11, 3G, CDPD, GSM, Bluetooth, Ricochet • Infostations (Rutgers) • When a client is in the proximity of the server, it access the data • Peer-to-Peer • Routing in mobile, ad hoc & sensor networks

8. Mobile information access Interactivity model : • Synchronous • Users directly access or request the data • Asynchronous (using prefetching) • Hoarding (Coda [CMU], Seer [UCLA])

9. Limitations of infostations & wireless WAN • No communication infrastructure eg field operation missions, tunnels, subway • Emergency • Overloaded • Expensive • Wireless WAN access with low bit rates & high delays

10. Host A Host B Limitations of ad hoc networks • All hosts cooperative • Complete path for the communication of two hosts

11. Limitations of hoarding • Only files • Files exist prior to disconnection • No dynamic generated information

12. Wireless data services • Delay tolerant • Location-dependent services • User location hints at data needs • Overhead to discover, access & update local data

13. Challenge Accelerate data availability & enhance dissemination & discovery of information under bandwidth changes & intermittent connectivity to the Internet due to host mobility considering power, bandwidth & memory constraints of hosts

14. Our Approach Increase data availability by enabling devices to share resources • Information sharing • Message relaying • Bandwidth sharing • Self-organizing • No infrastructure • Exploit host mobility

15. Outline • Introduction • Background on wireless data access • Motivation • Overview of 7DS • Simulations & Analysis on 7DS • Information dissemination • Message relaying • Bandwidth sharing • Conclusions • Future work

16. 7DS • Application • Zero infrastructure • Relay, search, share & disseminate information • Generalization of infostation • SporadicallyInternet connected • Coexistswith other data access methods • Communicates with peers via a wireless LAN • Power/energy constrained mobile nodes

17. traffic, weather, maps, routes, gas station Examples of services using 7DS news WAN events in campus, pictures where is the closest Internet café ? pictures, measurements service location queries schedule info autonomous cache

18. WLAN query WAN Host D data query Host A Information sharing with 7DS cache miss Host C WLAN cache hit data Host B Host A

19. Power conservation • server to client • only servershares data • no cooperation among clients • fixed info server (infostation model) • mobile info server communication enabled on off time Forwarding FW query query • peer to peer • data sharing among peers Host C Host A Host B time 7DS options Cooperation Server to client Peer to peer Querying active (periodic) passive

20. Outline • Introduction • Simulations & Analysis on 7DS • Information dissemination • Message relaying • Bandwidth sharing • wireless LAN • video on demand environment • Conclusions • Future work

21. Simulation environment pause time 50 s mobile user speed 0 .. 1.5 m/s host density 5 .. 25 hosts/km2 wireless coverage 230 m (H), 115 m (M), 57.5 m (L) ns-2 with CMU mobility, wireless extension & randway model querier wireless coverage dataholder randway model

22. Simulation environment pause time 50 s mobile user speed 0 .. 1.5 m/s host density 5 .. 25 hosts/km2 wireless coverage 230 m (H), 115 m (M), 57.5 m (L) ns-2 with CMU mobility, wireless extension querier wireless coverage 1m/s pause mobile host data holder

23. data v2 v3 Simulation environment pause time 50 s mobile user speed 0 .. 1.5 m/s host density 5 .. 25 hosts/km2 wireless coverage 230 m (H), 115 m (M), 57.5 m (L) ns-2 with CMU mobility, wireless extension wireless coverage v1

24. Dataholders (%) after 25 min high transmission power P2P Mobile Info Server Fixed Info Server 2

25. 2 km 1 km 1 km Scaling properties of data dissemination wireless coverage R R 2 km If cooperative host density & transmission power are fixed, data dissemination remains the same

26. Scaling properties of data dissemination (cont’d) wireless coverage R R/2 For fixed wireless coverage, the larger the densityofcooperative hosts, the more efficient the data dissemination

27. Average delay (s) vs. dataholders (%) Fixed Info Server one server in 2x2 high transmission power 4 servers in 2x2 medium transmission power

28. Average Delay (s) vs Dataholders (%)Peer-to-Peer schemes high transmission power medium transmission power

29. r/2 v x x R/2 Scaling properties of data dissemination (cont’d) L wireless coverage of info server r v L x x R

30. trapping model with particles C and T (traps) particles C perform random walk in 2D space particles T static, randomly distributed in space of infinite capacity particles T absorb C when C step onto them survival probability fn at long times n log (fn)  -An T C Modeling Fixed Info Server as diffusion-controlled process querier  particle C fixed info server trap trappingreceiving data

31. Fixed Info Serversimulation and analytical results high transmission power Probability a host will acquire data by time t follows 1-e-at

32. Outline • Introduction • Background on wireless data access • Motivation • Overview of 7DS • Performance analysis on 7DS • Information dissemination • Message relaying • Network connection sharing • Conclusions • Future work

33. WLAN messages Host A Message relaying with 7DS WAN Gateway WLAN Message relaying Host B Host A

34. Message relaying • Take advantage of host mobility to increase throughput • Hosts buffer messages & forward them to a gateway • Hosts forward their own messages to cooperative relay hosts • Restrict number of times hosts forwards

35. Messages (%) relayed after 25 min(average number of buffered messages : 5) 2

36. Outline • Introduction • Background • Motivation • Overview of the system • Performance analysis • Information dissemination • Message relaying • Network connection sharing • Conclusions • Future work

37. Network connection sharing Host F WAN Host E Host A thin WAN links Hosts A & B dual-homed They act as gateways to WAN for hosts C & D Host D Wireless LAN Host C Host B

38. Network connection sharingprotocol Host E WAN • Csends request for gateway • B & Arespond advertising their bandwidth in WAN link • 4.C selects least loaded gateway (eg A) • 5.A  Cadmission control thin wireless WAN links HostA HostD WLAN Host B Host C

39. Benefits using network connection sharing • Statistical multiplexing for bursty traffic • Increase bandwidth utilization of the WAN links • 80% bandwidth utilization for Pareto traffic • Load balancing across gateways • For shared data applications : • Reduction of replicated data • Increase quality of service

40. Outline • Introduction • Background on wireless data access • Motivation • Overview of the system • Performance analysis • Information dissemination • Message relaying • Network connection sharing • Conclusions • Future work

41. Conclusions • Dominant parameters: • density of cooperative hosts • wireless coverage density of cooperative hosts & their mobility • For fixed cooperative hosts density & transmission power : scale area performance same • For fixed wireless coverage density : Density of cooperative host  performance 

42. Conclusions (cont’d) • Probability a host will acquire data by time t in • Fixed Info Server : 1-e-at • Peer-to-Peer : 1-e-at • Message relaying is beneficial : • Probability a message will reach the Internet  • Utilization of available throughput  by taking advantage of host mobility

43. Future work • Location-dependent applications & services • Actual traces & models for user mobility, access patterns & data locality • Enhanced power conservation mechanism • Security & micro-payment issues • Extension of network connection protocol • Generalization of diffusion models for P2P • Adaptive scalable algorithms for information discovery

44. Summary of contributions in video on demand Novel multimedia retrieval scheduling algorithms In multi-disk environments : • adapt to bandwidth changes • maximize data retrieval forall streams using replication and multi-resolution In single-disk environments : • allocatedisk bandwidth in a fair manner

45. Thank you!

46. Future work: short term • More on power conservation for data dissemination • Peer-to-peer scheme using diffusion controlled processes • Prototype • Deployment of 7DS in CU campus & in Bremen • Public release of the code • Collaborations • IBM, HP, Bertelsmann & Limewire (Gnutella)

47. Future work : longer term • Information discovery & dissemination in pervasive computing • Model & abstractions for the quality of information • Tight energy, bandwidth • Privacy & security for mobile, peer-to-peer applications • Scaling & structural properties

48. multicast query wait to hear if Q is challenged multicast challenge run non-trivial computational task sends response Preventing DoS attacks Host Q Host R receives query verifies Q’s answer decides to cooperate

49. send credentials send e-check wait for data from R send data Electronic check payment Host Q Host R verify R is known to the bank & authorized for 7ds receive e-check verify it is genuine store e-check

50. send public key with report form query send query wait for data from R send data decrease counter send ack decrease counter send nack Token-based payment Host Q Host R check token counter verify R’s public key receive query increase token counter increase token counter senddata