Henning Schulzrinne

1

• Henning Schulzrinne
• Maria Papadopouli
• Computer Science Department
• Columbia University
• http//www.cs.columbia.edu/IRT

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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
bandwidth (peak)
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Cost of networking
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Wireless WAN access

• Spectrum is very expensive

• 3G bandwidth is very low (64 kb/s)

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New wireless modes

• High upstream cost ? caching
• cf. early Internet (Australia)
• expand reach by leveraging mobility
• locality of data references
• mobile Internet not for general research
• Zipf distribution for multimedia content
• newspapers
• local information (maps, schedules, traffic,
  weather, tourist information)

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A family of access points
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NYC wireless public infrastructure
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Background

• Fast growth in pervasive computing devices
• Fast wireless data services growth
• Base stations for wireless WAN will not keep pace
• Regulatory, environmental cost barriers for a
  dense deployment
• Users experience intermittent connectivity
  limited data access

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Mobile information access

• Dependency on infrastructure
• Wireless WAN
• eg 802.11, 3G, CDPD, GSM, Bluetooth, Ricochet
• Infostations (Rutgers)
• When a client is in the proximity of the server,
  it access the data
• Peer-to-Peer
• Routing in mobile, ad hoc sensor networks

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Mobile information access

• Interactivity model
• Synchronous
• Users directly access or request the data
• Asynchronous (using prefetching)
• Hoarding (Coda CMU, Seer UCLA)

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Limitations of infostations wireless WAN

• No communication infrastructure
• eg field operation missions, tunnels,
  subway
• Emergency
• Overloaded
• Expensive
• Wireless WAN access with low bit rates high
  delays

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Limitations of ad hoc networks

• All hosts cooperative
• Complete path for the communication of two hosts

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Limitations of hoarding

• Only files
• Files exist prior to disconnection
• No dynamic generated information

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Wireless data services

• Delay tolerant
• Location-dependent services
• User location hints at data needs
• Overhead to discover, access update local data

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Challenge

• Accelerate data availability enhance
  dissemination discovery of information under
  bandwidth changes intermittent connectivity to
  the Internet due to host mobility
• considering power, bandwidth memory
  constraints of hosts

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Our Approach

• 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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Outline

• Introduction
• Background on wireless data access
• Motivation
• Overview of 7DS
• Simulations Analysis on 7DS
• Information dissemination
• Message relaying
• Bandwidth sharing
• Conclusions
• Future work

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7DS

• Application
• Zero infrastructure
• Relay, search, share disseminate information
• Generalization of infostation
• Sporadically Internet connected
• Coexists with other data access methods
• Communicates with peers via a wireless LAN
• Power/energy constrained mobile nodes

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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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7DS options
Cooperation Server to client Peer to peer
Querying active (periodic) passive
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Outline

• Introduction
• Simulations Analysis on 7DS
• Information dissemination
• Message relaying
• Bandwidth sharing
• wireless LAN
• video on demand environment
• Conclusions
• Future work

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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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Scaling properties of data dissemination
wireless coverage

R
R
2 km
If cooperative host density transmission power
are fixed, data dissemination remains the same
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Scaling properties of data dissemination (contd)
wireless coverage
R
R/2
For fixed wireless coverage, the larger the
density of cooperative hosts, the more efficient
the data dissemination
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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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Scaling properties of data dissemination (contd)
L
wireless coverage of info server
r
v
L
x
x
R
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Modeling Fixed Info Server as diffusion-controlled
process

• trapping model with particles C and T (traps)
• particles C perform random walk in 2D space
• particles T static, randomly distributed in space
  of infinite capacity
• particles T absorb C when C step onto them

querier ? particle C
fixed info server ? trap
trapping ? receiving data

• survival probability fn at long times n
• log (fn) ? -A?n

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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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Outline

• Introduction
• Background on wireless data access
• Motivation
• Overview of 7DS
• Performance analysis on 7DS
• Information dissemination
• Message relaying
• Network connection sharing
• Conclusions
• Future work

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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
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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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Outline

• Introduction
• Background
• Motivation
• Overview of the system
• Performance analysis
• Information dissemination
• Message relaying
• Network connection sharing
• Conclusions
• Future work

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Network connection sharing
Host F
WAN
Host E
Host A
thin WAN links
Hosts A B dual-homed They act as gateways to
WAN for hosts C D
Host D
Wireless LAN
Host C
Host B
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Network connection sharingprotocol
Host E
WAN

• C sends request for gateway
• B A respond advertising their bandwidth in WAN
  link
• 4. C selects least loaded gateway (eg A)
• 5. A ? C admission control

thin wireless WAN links
Host A
Host D
WLAN
Host B
Host C
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Benefits using network connection sharing

• Statistical multiplexing for bursty traffic
• Increase bandwidth utilization of the WAN links
• 80 bandwidth utilization for Pareto traffic
• Load balancing across gateways
• For shared data applications
• Reduction of replicated data
• Increase quality of service

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Outline

• Introduction
• Background on wireless data access
• Motivation
• Overview of the system
• Performance analysis
• Information dissemination
• Message relaying
• Network connection sharing
• Conclusions
• Future work

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Conclusions

• Dominant parameters
• density of cooperative hosts
• wireless coverage density of cooperative hosts
  their mobility
• For fixed cooperative hosts density
  transmission power
• scale area performance
  same
• For fixed wireless coverage density
• Density of cooperative host ?
  performance ?

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Conclusions (contd)

• Probability a host will acquire data by time t
  in
• Fixed Info Server 1-e-a?t
• Peer-to-Peer 1-e-at
• Message relaying is beneficial
• Probability a message will reach the Internet ?
• Utilization of available throughput ?
• by taking advantage of host mobility

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Future work

• Location-dependent applications services
• Actual traces models for user mobility, access
  patterns data locality
• Enhanced power conservation mechanism
• Security micro-payment issues
• Extension of network connection protocol
• Generalization of diffusion models for P2P
• Adaptive scalable algorithms for information
  discovery

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Future work short term

• More on power conservation for data dissemination
  
• Peer-to-peer scheme using diffusion controlled
  processes
• Prototype
• Deployment of 7DS in CU campus in Bremen
• Public release of the code
• Collaborations
• IBM, HP, Bertelsmann Limewire (Gnutella)

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Future work longer term

• Information discovery dissemination in
  pervasive computing
• Model abstractions for the quality of
  information
• Tight energy, bandwidth
• Privacy security for mobile, peer-to-peer
  applications
• Scaling structural properties

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Preventing DoS attacks
Host Q
Host R
receives query
verifies Qs answer
decides to cooperate
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Electronic check payment
Host Q
Host R
verify R is known to the bank authorized for
7ds
receive e-check verify it is genuine store
e-check
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Token-based payment
Host Q
Host R
check token counter
verify Rs public key
receive query
increase token counter
increase token counter send data
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Information discovery dissemination in
pervasive computing

• Query data locality
• No need of infrastructure use 7DS
• Query routing required
• Use infrastructure of gateways that create
  peer-to-peer overlay hierarchies in
  self-organizing manner based on query demand
  resources
• Castro, Greenstein, Muntz, Bisdikian,
  Kermani, Papadopouli Locating Application Data
  Across Service Discovery Domains, MOBICOM01

58
Message relayed to gateway after 25 min
2
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Network connection sharing summary
Client
Gateway

• Requests for network connection
• Gateway selection
• Load balancing criteria

• Advertisement of gateway availability
• Admission control using Measured sum Jamin et
  al
• u? ? vr
• v measured load
• r (peak) rate requested
• uutilization target
• ?bandwidth of WAN link

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Gateway selection mechanism

• Load balancing criteria
• Reduction of the maximum difference in
• the average load over an interval t across the
  gateways
• maxiLi(t)-miniLi(t)/b
• Li(t) average traffic measured at gateway i
  over interval t
• Greedy algorithm Choose the least loaded gateway

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Network connection sharing
Pareto exponential 312 s(ON), 325s
(OFF) Pareto, shape par. 1.2 Flows 64kb/s,
0.6 s int., avg hold time 5 min Perfect load
balancing 0
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Pareto traffic measurement policy
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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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Information discovery in pervasive computing
Castro, Greenstein, Muntz (UCLA), Bisdikian,
Kermani (IBM), Papadopouli (Columbia Un.),
Locating Application Data Across Service
Discovery Domains, MOBICOM 2001.

• Dynamic nature of the environment
• uncertainty, errors, timeliness redundancy
• Local autonomy
• Partial knowledge, local decisions to achieve a
  global effect
• Self-organization to minimize administration
  overhead
• Adaptive, scalable algorithms protocols

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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

N-1
i1
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Mobility models

• User mobility
• Randway
• Random direction
• Boundless simulation area
• Gauss-Markov
• with history of previous move

• Group mobility
• Column mobility
• Pursue mobility
• Nomadic community mobility

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Subway model

• Passengers arrive at subway stations
• Poisson process 1/l1-3min
• ride 2-6 stops
• 1 min to leave the platform
• Subway line
• 10 stops
• Train with 6 cars
• Arrives at a stop every 5 minutes
• Percentage of dataholders after they leave the
  subway for 1/l 3 min is 65

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Types of attacks in ad hoc networks

• Basic mechanisms
• MAC layer
• Routing mechanisms
• Malicious users agree to forward messages but
  fail to do so
• False routing information messages
• Selfishness service enforcement issues

• Security mechanisms
• Distributed trusted server under the control of
  malicious party
• Public key maliciously replaced

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Service enforcement

• Lock out mechanism for selfish or misbehaving
  users
• Denial of service attacks
• Locked out node moves away where his behavior is
  not reported
• Virtual micro currency mechanism
• Incentives to cooperate
• Discouraged from overloading the network
• terminodes.org (EPFL), mojonation.net

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Virtual micro currency

• Nodes remunerate each other for the services they
  provide to each other
• terminodes.org (EPFL), mojonation.net

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Information discovery dissemination in
pervasive computing

• Dynamic nature of the environment
• Uncertainty, errors, timeliness redundancy
• Local autonomy
• Partial knowledge, local decisions to achieve a
  global effect
• Self-organization
• Minimize administration overhead
• Adaptive, scalable algorithms protocols

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Avantgo wireless service provider
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Vindigo wireless service provider