Using Low-Speed Links for High-Speed Wireless Data Delivery

Transcription

1 Using Low-Speed Links for High-Speed Wireless Data Delivery Henning Schulzrinne Dept. of Computer Science Columbia University (with Stelios Sidiroglou and Maria Papadopouli) ORBIT Research Review - May 13,

2 Overview Disconnected ad-hoc networks multi-modal networking using low-speed feedback to accelerate data delivery 7DS prototype future work ORBIT Research Review - May 13,

3 Wireless Network: filling the infrastructure-ad hoc gap Wireless networks: Ubiquitous, fast, cheap: pick any two Currently, varies from 0.1c to $4/MB Research has primarily explored: one-hop infrastructure extension (2G, 3G, ) multi-hop connected ad-hoc networks (mesh networks) But: 2G/3G bandwidth will remain low and precious hot spots not ubiquitous ad hoc networks don t scale brittle if spanning large areas Our proposal: use mobile nodes to carry data to and from infrastructure networks ORBIT Research Review - May 13,

4 Cost of networking Modality mode speed $/MB (= 1 minute of 64 kb/s videoconferencing or 1/3 MP3) OC-3 P 155 Mb/s $ Australian DSL (512/128 kb/s) P 512/128 kb/s $0.018 GSM voice C 8 kb/s $0.66-$1.70 HSCSD C 20 kb/s $2.06 GPRS P 25 kb/s $4-$10 Iridium C 10 kb/s $20 SMS (160 chars/message) P? $62.50 Motient (BlackBerry) P 8 kb/s $133 ORBIT Research Review - May 13,

5 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 ORBIT Research Review - May 13,

6 7DS a framework for intermittently connected networks Two directions for data: Internet mobile nodes mobile nodes Internet high low Each in multiple hops but not routed high low 7DS satellite SMS? hotspots voice (2G, 2.5G) 7DS = seven degrees of separation ORBIT Research Review - May 13,

7 Applications Tourism: get information about sights, travel, public transport schedules,.. upload picture postcards and video recordings Transportation: users in buses and trains leverage data capability Emergencies: propagate I m alive and rescue information Mobile sensors: sensors spread too far to communicate directly with each other large sensor data objects ORBIT Research Review - May 13,

8 A family of access points WLAN Connected Infostation Disconnected Infostation 2G/3G access sharing 7DS ORBIT Research Review - May 13,

9 Network to Mobile Deliver web content to roaming user weather? query for all documents multicast deliver matching documents 7DS node web cache ORBIT Research Review - May 13,

10 Simulation environment )! "!# $ %" &! '( ORBIT Research Review - May 13,

11 Average Delay (s) vs Dataholders (%) Peer-to-Peer schemes Average Delay (s) Dataholders (%) P2P (high transmission power) one initial dataholder & 20 cooperative hosts in 2x2 P2P(medium transmission power) one initial dataholder & 20 coperative hosts in 1x1 ORBIT Research Review - May 13,

12 Modeling 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 Σ +, * +, Statistical mechanics model can accurately predict data distribution for some scenarios ORBIT Research Review - May 13,

13 Mobile to Internet service interface propagate to other pedestrians 7DS MTA encrypt message; encrypt headers with 7DS public key ORBIT Research Review - May 13,

14 Realization ORBIT Research Review - May 13,

15 Closing the loop in 7DS Problems with open-loop propagation systems Network to mobile no way to inject popular content into the system Mobile to network have to limit replication to avoid flooding If too few copies, may never get delivered copies persist long after delivery succeeded Thus, transform into closedloop system don t know who needs information but likely regionally limited by mobility regional broadcast of control information no need for bidirectional data low bandwidth ORBIT Research Review - May 13,

16 Options for closing the loop Options: satellite radio (XM, Sirius) LEO satellites (Iridium) low-bandwidth cellular (CDPD, GSM) one-way or two-way pagers See also: Ambient Devices ORBIT Research Review - May 13,

17 Pagers as feedback channel FLEX b/s remove from cache SNPP (RFC 1861) MTA message 42 delivered PL-900 POCSAG ORBIT Research Review - May 13,

18 Cache management details Receiving MTA broadcasts unique (hash) identifier of message hash long enough to prevent spoofing 7DS nodes remove from cache other MTAs prevent delivery Popularity management indications of popular content distributed to 7DS nodes nodes query that content from others Reputation management distribute identifier for good and bad guys good guys: deliver messages fast bad guys: never deliver messages accept messages preferably from good guys ORBIT Research Review - May 13,

19 Current status: prototype Initial Java implementation search not just by URL, but by content greater likelihood of finding appropriate material ( news ) Working on PDA implementations Also, considering Linux embedded systems low-power, self-contained ORBIT Research Review - May 13,

20 7DS node ORBIT Research Review - May 13,

21 On-going work: leveraging low-bandwidth links Hordes of low-bandwidth nodes: split large or urgent message into pieces spread pieces across many nodes each node transmits at very low rate use Tornado codes for redundancy cf. BitTorrent ORBIT Research Review - May 13,

22 Conclusion 7DS as extension of infrastructure and adhoc networks Combine benefits of low bit-rate, but ubiquitous and high bit-rate, but sparse networks ORBIT Research Review - May 13,