Multimodal Wireless Networking: From Message Forwarding to Infrastructure Networks

1. Multimodal Wireless Networking: From Message Forwarding to Infrastructure Networks Henning Schulzrinne Maria Papadopouli Computer Science Department Columbia University http://www.cs.columbia.edu/IRT

2. Outline • Introduction • A taxonomy of wireless networks • Motivation • Overview of 7DS • Performance analysis on 7DS • Conclusions • Future work

3. Multimodal networking • "The term multimodal transport is often used loosely and interchangeably with the term intermodal transport. Both refer to the transport of goods through several modes of transport from origin to destination." (UN) • goods packaged in containers  packets and messages • Networking  combine different modes of data transport that maximize efficiency

4. Multimodal networking • Speed, cost and ubiquity are the core variables • cf. pipelines, ships, planes, trucks • Traditional assumption of value of immediacy from PSTN  demise of Iridium

5. Access modalities delay bandwidth (peak)

6. Cost of networking

7. Wireless WAN access • Spectrum is very expensive • 3G bandwidth is very low (64 kb/s)

8. New wireless modes • High upstream cost  caching • cf. early Internet (Australia) • expand reach by leveraging mobility • locality of data references • mobile Internet not for general research • Zipf distribution for multimedia content • newspapers • local information (maps, schedules, traffic, weather, tourist information)

9. 2G/3G WLAN hotspot + cache Infostation access sharing 7DS A family of access points

10. NYC wireless public infrastructure

11. 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

12. 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

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

14. 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

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

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

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

18. 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

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

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

21. 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

22. 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

23. 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

24. 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

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

26. 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

27. 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

28. 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

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

30. 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

31. 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

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

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

34. 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

35. 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

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

37. 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

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

39. 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

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

41. 7DS Implementation • Cache manager (3k lines) • GUI server (2k lines) • HTTP client & methods (24k lines) • Proxy server (1k lines) • UDP multicast & unicast (1k) • Web client & server (2k) • Jar files used (xerces, xml,lucene, html parcer)

42. 7DS implementation • Initial Java implementation on laptop • Compaq Ipaq (Linux or WinCE) • Inhand Electronics ARM RISC board • Low power • PCMCIA slot for storage, network or GPS

43. 7DS implementation

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

45. 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

46. 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

47. 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

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

49. 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 

50. 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