1 Multimodal Wireless Networking: From Message Forwarding to Infrastructure Networks Henning Schulzrinne joint work with Maria Papadopouli and Stelios Sidiroglou Computer Science Department Columbia University

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 highlow high7DS hotspots lowsatellite SMS? voice (2G, 2.5G) bandwidth (peak) delay

6 Cost of networking Modality modespeed $/MB (= 1 minute of 64 kb/s videoconferencing or 1/3 MP3) OC-3P 155 Mb/s $ Australian DSL (512/128 kb/s) P 512/128 kb/s $0.018 GSM voiceC 8 kb/s $0.66-$1.70 HSCSDC 20 kb/s $2.06 GPRSP 25 kb/s $4-$10 IridiumC 10 kb/s $20 SMS (160 chars/message) P ? $62.50 Motient (BlackBerry) P 8 kb/s $133

7 Wireless WAN access Location whatcost UK3G$590/person Germany3G$558/person Italy3G$200/person New YorkVerizon (20MHz) $220/customer Spectrum is very expensive 3G bandwidth is very low (around 60 kb/s)

8 Limitations of Good for hotspots, difficult for complete coverage Manhattan = 60 km 2  6,000 base stations (not counting vertical) –With ~ 600,000 Manhattan households, 1% of households would have to install access points Almost no coverage outside of large coastal cities

9 Mobile data access Hoarding: grab data before moving , 3G, BlueTooth: wireless as last-hop access technology Ad-hoc networks: –Wireless nodes forward to each other –Routing protocol determines current path –Requires connected network, some stability –Mobility harmful (disrupts network) 7DS networks: –No contiguous connectivity –Temporary clusters of nodes –Mobility helpful (propagates information)

10 A family of access points Disconnected Infostation 2G/3G access sharing 7DS Connected Infostation WLAN

11 Limitations of infostations & wireless WAN Require communication infrastructure not available field operation missions, tunnels, subway Emergency Overloaded Expensive Wireless WAN access with low bit rates & high delays

12 Our Approach: 7DS 7DS = Seven Degrees of Separation Increase data availability by enabling devices to share resources –Information sharing –Message relaying –Bandwidth sharing Self-organizing No infrastructure Exploit host mobility

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

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

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

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

17 Simulation environment pause time 50 s mobile user speed m/s host density hosts/km 2 wireless coverage 230 m (H), 115 m (M), 57.5 m (L) ns-2 with CMU mobility, wireless extension v1v1 v2v2 v3v3 wireless coverage data

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

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

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

21 Fixed Info Server simulation and analytical results Probability a host will acquire data by time t follows 1-e -a  t high transmission power

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

23 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

24 2 Messages (%) relayed after 25 min (average number of buffered messages : 5)

25 7DS node

26 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)

27 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

28 7DS implementation

29 2 Message relayed to gateway after 25 min

30 Information discovery & dissemination in pervasive computing Without infrastructure : –7DS exploits query & data object locality & host mobility –Cooperation among hosts based on resources With infrastructure : –Gateways create peer to peer overlay hierarchies in self-organizing manner –Participate based on query demand & resources Castro,Greenstein,Muntz (UCLA), Bisdikian,Kermani(IBM), Papadopouli(Columbia Un.), “Locating Application Data Across Service Discovery Domains”, MOBICOM’01

31 Epidemic model Carrier is “infected”, hosts are “susceptible” Transmit to any give host with probability ha+o(h) in interval h Pure birth process T=time until data has spread among all mobiles E[T]=1/a  i=1 N-1 i(N-1) 1