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Multimodal Wireless Networking: From

Message Forwarding to Infrastructure Networks

Henning Schulzrinnejoint work with

Maria Papadopouli and Stelios Sidiroglou

Computer Science DepartmentColumbia University

http://www.cs.columbia.edu/IRThgs@cs.columbia.edu

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Outline

• Introduction– A taxonomy of wireless networks– Motivation– Overview of 7DS

• Performance analysis on 7DS• Conclusions • Future work

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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

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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

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Access modalities

high lowhigh 7DS 802.11

hotspotslow satellite

SMS?voice (2G, 2.5G)ba

ndwi

dth

(pea

k)delay

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Cost of networkingModality mod

espeed $/MB (= 1 minute of 64

kb/s videoconferencing or 1/3 MP3)

OC-3 P 155 Mb/s $0.0013Australian DSL(512/128 kb/s)

P 512/128 kb/s

$0.018

GSM voice C 8 kb/s $0.66-$1.70HSCSD C 20 kb/s $2.06GPRS P 25 kb/s $4-$10Iridium C 10 kb/s $20SMS (160 chars/message) P ? $62.50Motient (BlackBerry) P 8 kb/s $133

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Wireless WAN access

Location

what costUK 3G $590/personGermany

3G $558/person

Italy 3G $200/personNew York

Verizon(20MHz)

$220/customer

• Spectrum is very expensive

• 3G bandwidth is very low (around 60 kb/s)

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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

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Mobile data access• Hoarding: grab data before moving• 802.11, 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)

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A family of access points

Disconnected Infostation

2G/3G

access sharing7DS

Connected Infostation

WLAN

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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

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Our Approach: 7DS7DS = Seven Degrees of SeparationIncrease data availability by enabling devices to share

resources– Information sharing–Message relaying–Bandwidth sharing

• Self-organizing• No infrastructure• Exploit host mobility

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Examples of services using 7DS

schedule info

WAN

autonomous cache

newsevents in campus,pictures

where is the closest Internet café ?

service location queries

traffic, weather, maps, routes, gas station

pictures, measurements

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Information sharing with 7DS

Host B

Host Cdata cache

hit

cache miss

data

Host A

query

WAN Host A Host D

query

WLAN

WLAN

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Simulation environmentpause 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

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Simulation environmentpause 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

pause1m/s

mobile host data holder

querierwireless coverage

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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

v1

v2

v3

wireless coveragedata

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0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25

Density of hosts (#hosts/km )

Dat

ahol

ders

(%) P2P data sharing

(power cons.)

P2P data sharing

P2P data sharing & FW(power cons.)

Fixed Info Server

Mobile Info Server

Dataholders (%) after 25 minhigh transmission power

2

Fixed Info Server

Mobile Info Server

P2P

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Average delay (s) vs. dataholders (%)

0

200

400

600

800

1000

1200

0 5 10 15 20 25 30 35Dataholders (%)

Ave

rage

Del

ay (s

)

Fixed Info Server(medium transmission power) 4 initial dataholders (servers) in 2x2

Fixed Info Server (high transmission power ) one initial dataholder (server) in 2x2

one server in 2x2high transmission power

4 servers in 2x2medium transmission power

Fixed Info Server

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

0200400600800

1000120014001600

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

Ave

rage

Del

ay (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

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Fixed Info Serversimulation and analytical

results

0

20

40

60

0 500 1000 1500 2000 2500 3000Time (s)

Dat

ahol

ders

(%)

simulation model

Probability a host will acquire data by time t follows 1-e-at

high transmission power

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Message relaying with 7DS

Host B

Messagerelaying

Host A

messages

Gateway

WAN

Host A WLAN

WLAN

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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

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0

20

40

60

80

100

5 10 15 20 25Density of hosts (#hosts/km )

Mes

sage

rel

ayed

(%

)

High transmission power (No FW)High transmission power (FW 6)Medium transmission power (No FW)Medium transmission power (FW 6)

2

Messages (%) relayed after 25 min (average number of buffered

messages : 5)

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7DS node

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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)

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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

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7DS implementation

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020406080

100

5 10 15 20 25Density of hosts (#hosts/km )

Mes

sage

rel

ayed

(%)

High transmission power (No FW)High transmission power (FW 6)Medium transmission power (No FW)Medium transmission power (FW 6)

2

Message relayed to gateway after 25 min

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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 & resourcesCastro,Greenstein,Muntz (UCLA), Bisdikian,Kermani(IBM),

Papadopouli(Columbia Un.), “Locating Application Data Across Service Discovery Domains”, MOBICOM’01

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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