ORBIT Research Review - May 13, 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, 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, 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, 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

ORBIT Research Review - May 13, 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, DS – a framework for intermittently connected networks Two directions for data: Internet  mobile nodes mobile nodes  Internet Each in multiple hops but not routed highlow high7DS hotspots lowsatellite SMS? voice (2G, 2.5G) bandwidth (peak) delay 7DS = seven degrees of separation

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

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

ORBIT Research Review - May 13, 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

ORBIT Research Review - May 13, Average Delay (s) vs Dataholders (%) Peer-to-Peer schemes medium transmission power high transmission power

ORBIT Research Review - May 13, 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  Statistical mechanics model can accurately predict data distribution for some scenarios i=1 N-1 i(N-1) 1

ORBIT Research Review - May 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, Realization

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

ORBIT Research Review - May 13, 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, 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, DS node

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