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, 2004 1
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, 2004 2
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, 802.11) � 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, 2004 3
Cost of networking mode speed Modality $/MB (= 1 minute of 64 kb/s videoconferencing or 1/3 MP3) 155 Mb/s OC-3 P $0.0013 512/128 Australian DSL P $0.018 kb/s (512/128 kb/s) 8 kb/s GSM voice C $0.66-$1.70 20 kb/s HSCSD C $2.06 25 kb/s GPRS P $4-$10 10 kb/s Iridium C $20 ? SMS (160 chars/message) P $62.50 8 kb/s Motient (BlackBerry) P $133 ORBIT Research Review - May 13, 2004 4
Limitations of 802.11 � Good for hotspots, difficult for complete coverage � Manhattan = 60 km 2 � 6,000 base stations (not counting vertical) � With ~ 600,000 Manhattan households, 1% of households would have to install access points � Almost no coverage outside of large coastal cities ORBIT Research Review - May 13, 2004 5
7DS – a framework for intermittently connected networks � Two directions for data: ����� � Internet � mobile nodes high low � mobile nodes � Internet ��������� high 7DS 802.11 � Each in multiple hops ������ hotspots � but not routed low satellite voice (2G, 2.5G) SMS? 7DS = seven degrees of separation ORBIT Research Review - May 13, 2004 6
Applications � Tourism: � get information about sights, travel, public transport schedules, .. � upload picture postcards and video recordings � Transportation: � users in buses and trains leverage data capability � Emergencies: � propagate “I’m alive” and rescue information � Mobile sensors: � sensors spread too far to communicate directly with each other � large sensor data objects ORBIT Research Review - May 13, 2004 7
A family of access points WLAN Disconnected Infostation Connected Infostation 2G/3G 7DS ORBIT Research Review - May 13, 2004 8 access sharing
Network to Mobile � Deliver web content to roaming user “weather?” query for web all documents multicast cache 7DS node deliver matching documents ORBIT Research Review - May 13, 2004 9
Simulation environment ���������������� ������������������������������ ����������������������������� � ������������������������� �!� �������"�!��#������$� )������ ����������������� ���������� ������������� ���� �����%"&���������!� ����������'��������(� ������������� ORBIT Research Review - May 13, 2004 10
Average Delay (s) vs Dataholders (%) Peer-to-Peer schemes 1600 Average Delay (s) 1400 1200 1000 ����������������������� 800 600 400 ������������������������� 200 0 0 10 20 30 40 50 60 70 80 90 100 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, 2004 11
Modeling � Carrier is “infected”, hosts � Statistical mechanics are “susceptible” model can accurately � Transmit to any give host predict data distribution with probability ha+o(h) in for some scenarios interval h � Pure birth process � T=time until data has spread among all mobiles +,� � � E[T]=1/a Σ ��+,�� �*� ORBIT Research Review - May 13, 2004 12
Mobile to Internet � Email service interface propagate to other pedestrians 7DS MTA encrypt message; encrypt headers with 7DS public key ORBIT Research Review - May 13, 2004 13
Realization ORBIT Research Review - May 13, 2004 14
Closing the loop in 7DS � Problems with open-loop � Thus, transform into closed- propagation systems loop system Network to mobile don’t know who needs � � information � no way to inject popular content into the system but likely regionally limited � by mobility Mobile to network � � regional broadcast of � have to limit replication to � avoid flooding control information � If too few copies, may no need for bidirectional � never get delivered data � copies persist long after low bandwidth � delivery succeeded ORBIT Research Review - May 13, 2004 15
Options for closing the loop � Options: � satellite radio (XM, Sirius) � LEO satellites (Iridium) � low-bandwidth cellular (CDPD, GSM) See also: Ambient Devices � one-way or two-way pagers ORBIT Research Review - May 13, 2004 16
Pagers as feedback channel FLEX 1600-6400 b/s remove from cache SNPP (RFC 1861) MTA “message 42 delivered” PL-900 POCSAG ORBIT Research Review - May 13, 2004 17
Cache management details � Receiving MTA broadcasts � Reputation management unique (hash) identifier of distribute identifier for good � message and bad guys hash long enough to good guys: deliver � � prevent spoofing messages fast 7DS nodes remove from bad guys: never deliver � � cache messages other MTAs prevent accept messages � � delivery preferably from good guys � Popularity management indications of popular � content distributed to 7DS nodes nodes query that content � from others ORBIT Research Review - May 13, 2004 18
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, 2004 19
7DS node ORBIT Research Review - May 13, 2004 20
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, 2004 21
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 ORBIT Research Review - May 13, 2004 22
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