Henning Schulzrinne

1

• Henning Schulzrinne
• joint work with
• Maria Papadopouli and Stelios Sidiroglou
• Computer Science Department
• Columbia University
• http//www.cs.columbia.edu/IRT
• hgs_at_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
delay
high low
high 7DS 802.11 hotspots
low satellite SMS? voice (2G, 2.5G)
bandwidth (peak)
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Cost of networking
Modality 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
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Wireless WAN access

• Spectrum is very expensive

Location what cost
UK 3G 590/person
Germany 3G 558/person
Italy 3G 200/person
New York Verizon (20MHz) 220/customer

• 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
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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 7DS

• 7DS Seven Degrees of Separation
• Increase 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
news
WAN
events in campus, pictures
where is the closest Internet café ?
pictures, measurements
service location queries
schedule info
autonomous cache
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Information sharing with 7DS
cache miss
Host C
WLAN
cache hit
data
Host B
Host A
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Simulation environment
pause time 50 s mobile user speed 0 .. 1.5
m/s host 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
querier
wireless coverage
dataholder
randway model
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Simulation environment
pause time 50 s mobile user speed 0 .. 1.5
m/s host density 5 .. 25 hosts/km2 wireless
coverage 230 m (H), 115 m (M), 57.5 m
(L) ns-2 with CMU mobility, wireless
extension
querier
wireless coverage
1m/s
pause
mobile host
data holder
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Simulation environment
pause time 50 s mobile user speed 0 .. 1.5
m/s host density 5 .. 25 hosts/km2 wireless
coverage 230 m (H), 115 m (M), 57.5 m
(L) ns-2 with CMU mobility, wireless
extension
wireless coverage
v1
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Dataholders () after 25 min
high transmission power
P2P
Mobile Info Server
Fixed Info Server
2
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Average delay (s) vs. dataholders ()
Fixed Info Server
one server in 2x2 high transmission power
4 servers in 2x2 medium transmission power
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Average Delay (s) vs Dataholders ()Peer-to-Peer
schemes
high transmission power
medium transmission power
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Fixed Info Serversimulation and analytical
results
high transmission power
Probability a host will acquire data by time t
follows 1-e-a?t
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Message relaying with 7DS
WAN
Gateway
WLAN
Message relaying
Host B
Host A
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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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Messages () relayed after 25 min (average
number of buffered messages 5)
2
25
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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Message relayed to gateway after 25 min
2
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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 resources
• Castro,Greenstein,Muntz (UCLA),
  Bisdikian,Kermani(IBM), Papadopouli(Columbia
  Un.), Locating Application Data Across Service
  Discovery Domains, MOBICOM01

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Epidemic model

• Carrier is infected, hosts are susceptible
• Transmit to any give host with probability
  hao(h) in interval h
• Pure birth process
• Ttime until data has spread among all mobiles
• ET1/a S

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