orbit research review - may 13, 20041 using low-speed links for high-speed wireless data delivery...

ORBIT Research Review - May 13, 2004 1

Using Low-Speed Links for High-Speed Wireless

Data Delivery

Henning SchulzrinneDept. of Computer Science

Columbia University(with Stelios Sidiroglou and Maria Papadopouli)


Overview

Disconnected ad-hoc networks multi-modal networking using low-speed feedback to accelerate data

delivery 7DS prototype future work


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


Cost of networkingModality mode speed $/MB (= 1 minute of 64 kb/s

videoconferencing or 1/3 MP3)

OC-3 P 155 Mb/s $0.0013

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


Limitations of 802.11

Good for hotspots, difficult for complete coverage Manhattan = 60 km2 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


7DS – a framework for intermittently connected networks

Two directions for data: Internet mobile nodes mobile nodes Internet

Each in multiple hops but not routed

high low

high 7DS 802.11

hotspots

low satellite

SMS?

voice (2G, 2.5G)b

andw

idth

(peak)

delay

7DS =seven degrees of

separation


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


A family of access points

Disconnected Infostation

2G/3G

access sharing7DS

Connected Infostation

WLAN


Network to Mobile

Deliver web content to roaming user

deliver matchingdocuments

“weather?”

multicast

query forall documents

webcache

7DSnode


Simulation environment

pause time 50 smobile user speed 0 .. 1.5 m/shost 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

dataholder

querier

randway model

wireless coverage


Average Delay (s) vs Dataholders (%)Peer-to-Peer schemes

0200400600800

1000120014001600

0 10 20 30 40 50 60 70 80 90 100Dataholders (%)

Ave

rag

e D

elay

(s)

P2P (high transmission power) one initial dataholder & 20 cooperative hosts in 2x2

P2P(medium transmission power) one initial dataholder & 20 coperative hosts in 1x1

medium transmission power

high transmission power


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


Mobile to Internet

Email service interface

propagate to otherpedestrians

7DSMTA

encrypt message;encrypt headers with 7DS public key


Realization


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


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


Pagers as feedback channel

MTA

PL-900 POCSAG

SNPP(RFC 1861)

FLEX1600-6400 b/s

“message 42 delivered”

removefrom

cache


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


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


7DS node


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


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, 20041 using low-speed links for high-speed wireless data delivery...

Documents