Networking for Pervasive Computing

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Networking for Pervasive Computing

• Hari Balakrishnan
• Networks and Mobile Systems Group
• MIT Laboratory for Computer Science
• http//nms.lcs.mit.edu/

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The real new, new thing

• Natural technology trends
• Computation is becoming essentially free
• Communication is becoming ubiquitous
• Smart devices
• Huge numbers of computing devices in the world
• What are we doing with them?
• Modes of operation
• Programs controlling other programs in our
  environment
• Human-in-the-loop computing should be only as
  visible as I desire no more, no less...

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MIT Project Oxygen

• Pervasive, human-centered computing
• Improve human productivity and comfort
• Move computation into the mainstream of our lives
• Improve ease-of-use and accessibility
• Do more by doing less
• The real challenge
• To develop a deep understanding of how to
  develop, deploy, and manage systems of systems in
  dynamic environments
• Build to use use to build

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The Oxygen environment
Situated computing
Camera array
Speech vision
Projector

Phone
Microphone array
- Handheld, mobile computers (e.g., Handy21) -
Situated computing resources sensors (e.g,
Enviro21) - Networked smart devices - And tons
of software making all this work together! User
technologies system software
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An exampleContext-aware network services

• Zero configuration

• Context-aware, location-based, speech-driven
  active maps

• Resource discovery and secure information access
• Unconstrained, adaptive mobility

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This talk context-aware networking

• Enable applications to adapt to real-world
  context and conditions
• Physical location
• Location-aware applications
• Requires location-support system (Cricket)
• User/application intent
• Resource discovery mechanism must allow
  applications to express what they want
• Intentional Naming System (INS)
• Mobility
• Devices using multiple networks at the same time
• Application-controlled end-to-end mobile routing
  to capture network context (Migrate)

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Cricket design goals

• Preserve user privacy
• Recognize spaces, not just physical position
• Good boundary detection is important
• Operate inside buildings
• Easy to administer and deploy
• Decentralized architecture and control
• Low cost and power consumption
• GPS-oriented solutions do not provide required
  precision, reliability, or cost-effectiveness

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Traditional approach
Location DB
ID u?
Networked sensor grid
ID u
Responder
Problems privacy administration granularity
cost
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Cricket Private location-support
Beacon
Pick nearest to infer space
Listener
No central beacon control or location
database Passive listeners active beacons
preserves privacy Straightforward deployment and
programmability
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Determining distance
Beacon
Ultrasound (pulse)
Listener

• A beacon transmits an RF and an ultrasonic signal
  simultaneously
• RF carries location data, ultrasound is a narrow
  pulse

• The listener measures the time gap between the
  receipt of RF and ultrasonic signals
• A time gap of x ms roughly corresponds to a
  distance of x feet from beacon
• Velocity of ultra sound ltlt velocity of RF

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Uncoordinated beacons
Beacon A
Beacon B
Incorrect distance
t
RF B
RF A
US B
US A

• Multiple beacon transmissions are uncoordinated
• Different beacon transmissions can interfere
• Causing inaccurate distance measurements at the
  listener

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Handling spurious interactions

• Combination of three different techniques
• Bounding stray signal interference
• Preventing repeated interactions via
  randomization
• Listener inference algorithms

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Bounding Stray Signal Interference

• RF range gt ultrasonic range
• Ensures an accompanied RF signal with ultrasound

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Bounding Stray Signal Interference

S size of space advertisement b RF bit
rate r ultrasound range v velocity of
ultrasound
(RF transmission time) (Max. RF-US
separation
at the listener)
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Bounding stray signal interference

RF B
US B
RF A
US A
t

• Envelop ultrasound by RF
• Interfering ultrasound causes RF signals to
  collide
• Listener does a block parity error check
• The reading is discarded

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Preventing repeated interactions

• Randomize beacon transmissions
• loop
• pick r UniformT1, T2
• delay(r)
• xmit_beacon(RF,US)
• Optimal choice of T1 and T2 can be calculated
  analytically
• Trade-off between latency and collision
  probability
• Erroneous estimates do not repeat

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Inference Algorithms

• MinMode
• Determine mode for each beacon
• Select the one with the minimum mode
• MinMean
• Calculate the mean distance for each beacon
• Select the one with the minimum value
• Majority (actually, plurality)
• Select the beacon with most number of readings
• Roughly corresponds to strongest radio signal

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Inference Algorithms
A
Frequency
B
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Distance (feet)
5
10
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Closest beacon may not reflect correct space
Room A
Room B
I am at B
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Correct beacon positioning
Room A
Room B
x
x
I am at A

• Position beacons to detect the boundary
• Multiple beacons per space are possible

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Implementation

• Cricket beacon and listener

RF
RF
Micro- controller
Micro- controller
RS232
US
US

• LocationManager provides an API to applications
• Integrated with intentional naming system for
  resource discovery

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Mobile listener performance
Room A
Room B
Room C
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Comparisons
System
Attribute
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Context-aware resource discovery

• Services advertise/register resources
• Consumers make queries for services
• System matches services and consumers
• This is really a naming problem
• Name services and treat queries are resolution
  requests
• Problem most of todays naming systems name by
  (network) locations
• Names should refer to what, not where

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Intentional names

• Expressive name language (like XML)
• Providers announce attributes
• Clients make queries
• Attribute-value matches
• Wildcard matches
• Ranges

service mit.edu/camera building NE43 room
510 resolution800x600 access
public status ready
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INS architecture
camera510.lcs.mit.edu
Lookup
image
Resolver self-configuration

• Intentional name resolvers
• form an overlay network

Late binding integrate resolution and message
routing
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Status

• Cricket v1 being deployed with location-aware
  applications using INS
• Lots of interesting deployment issues and
  interactions with the real-world
• INS deployed at LCS
• Starting to be used in wider Oxygen context
• Mobile applications using late-binding
• Cricket beacons disseminate INS vspaces
• Enabling technologies for location-aware
  applications
• http//nms.lcs.mit.edu/

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Cricket demo