Intelligent Fluid infrastructure for Embedded Networks Aman Kansal, Arun A Somasundara, David D Jea, Mani B Srivastava, Deborah Estrin. University of California, Los Angeles (UCLA)

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• Intelligent Fluid infrastructure for Embedded
  Networks Aman Kansal, Arun A Somasundara, David D
  Jea, Mani B Srivastava, Deborah Estrin.
  University of California, Los Angeles (UCLA)
• MobiSys 04, June 6-9, ACM 2004

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Outline

• Overview
• The Idea
• Advantages
• The system components of the infrastructure
• Hardware Prototype
• Control Primitives
• Communication Protocol
• Experimental Results
• Future Work

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Overview General Idea

• Fluid Infrastructure mobile components built
  into the system for enabling specific
  functionality that is very hard to achieve using
  other methods
• Built-in intelligence to adapt to achieve
  objectives
• Energy constraints, security, delay, sparse
  networks
• Founded on real world behavior of wireless
  devices not based on radio models Real time
  test
• Focus on Network Layer Functionality
• Sensor networks
• Mobility
• Random whales, zebra
• Predicted a network node mounted on a bus and
  acts like a base station for collecting data
• Controlled introduce an element of deliberate
  control over mobility controlled by the
  infrastructure
• Increase performance

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Overview - Advantages

• System lifetime ?
• Battery capacity of embedded static nodes.
  Replace/Recharge not feasible Physically not
  reachable, cost
• A mobile agent helps conserve energy at static
  nodes
• Reduce number of hops
• Reduce number of packets transmitted by static
  nodes
• Mobile nodes are not energy-constrained
• Static nodes are energy-constrained
• Assume Data gathering protocol
• Directed Diffusion broadcast INTEREST,
• Data in response via nodes from which INTEREST
  heard.

1-5 hops 1-2 hops - INTEREST
Transmission 60s. - INTEREST Expire 75s -
Sample Generation Period 5s - Samples Per Data
Packet 4 - 16 minutes simulation period,
TOSSIM - Stop at each node 60s
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Overview - Advantages

• Quality of data ?
• Reduce number of hops
• Probability of errors ?
• Reduce retransmissions at static nodes energy
  conserved

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Overview - Advantages

• Data Rate ? or Latency ?
• Network capacity increased physically carrying
  data in mobile router
• Collisions reduced
• Less hops error rate ?
• Mobile device has 802.11 connection with the
  base used only when at Base

• mica2 motes
• Each mote 512KB flash M 500KB
• stored
• 38.4Kbps baud rate
• Max speed of router 388 cm/s 200 cm/s
• used

• Tideal T(A,A,B) T(A,B,base) T(B,B,base)
• Tmobile D(base,A) T(A,A,mobile_router)
  D(A,B) T(B,B,mobile_router)
• D(B,base) T(A,B,mobile_route
  r,base).

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Overview - Advantages

• Handle Sparse (low density) Disconnected
  Networks
• Reduce transmission range to lowest value to
  reach the mobile router energy conserved
• To ensure connectivity 14
• Communication range 2Sensing range
• Use mobile agent instead of relay nodes that are
  just for connectivity energy conserved

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Overview - Advantages

• Others
• Time synchronization error decreases less hops
• Security enhanced data travels across less hops

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Overview The System

• Prototype hardware
• A sensor network
• An autonomous mobile router
• Real hardware for test usable methods
• Control primitives
• Control the motion of mobile routing components
• Communication protocol
• Changes with the nature of the system presence
  of mobile router

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System Architecture

• Motes Static embedded sensor nodes mica2 14
• A mobile router the fluid infrastructure
  connecting the static nodes to the base
• (The base could be a human
• user based system, or
• controller)

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System Architecture

• A traction platform Packbot
• A rugged terrain robot
• Unmanned ground vehicle
• 802.11 interface to get commands
• SIR (Simple Interface for Robots)
• only 2 API functions roboAct(), roboAdd() to
  move, rotate, and flip
• Runs only on Linux, and TinyOS
• Supports 2 robots Packbot, and Amigobot
• robotAct(id, f, 30) robot of ID id perform
  command f (move forward) with parameter 30
  (30 cm/s)
• robotAct(id, m, 30, 1.0, 1.0) robot id move
  to coordinate (1.0, 1.0) at 30 cm/s 2D.

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System Architecture

• Stargate 20
• Processing board xScale processor
• 802.11 card
• Communicate with the Base
• Send commands to the Packbot
• A mote network interface card (NIC)
• Communicate with static motes
• Software
• Localization, Navigation not complete
• Assumption obstacle free environment

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System Architecture

• The mobile routers Mote
• Relays data received from radio to Stargate
• Relays data from Stargate to radio
• Can be used to transfer data to the Base

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Adaptive Motion Control

• 2 factors
• Constraints due to the terrain
• Depending on terrain router can visit all nodes
  or a subset
• 1st Fluid Infrastructure is for gathering data
  from an ecosystem
• Mobility is restricted, and could lead to a
  disturbance to the habitat
• Motion control algorithms designed with the path
  traversed by the mobile node agent is fixed
• The data collection performance parameters

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Adaptive Motion Control

• 2 factors
• Constraints due to the terrain
• The data collection performance parameters
• Application priorities can be considered in the
  algorithm
• Max life time visit each node, least amount of
  energy in transmitting data should be used by
  embedded nodes
• Total amount of data collected
• static nodes generate data at rapid rate, router
  transfer max possible data to Base.
• Mobile router could use a hybrid topology
  (Multi-Hop mobile infrastructure)

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Adaptive Motion Control

• 2 factors
• Constraints due to the terrain
• The data collection performance parameters
• Latency maximize number of data collected within
  a period high speed of router
• Limited buffers of static nodes
• router to collect data before overflow
• Multi-hope may be needed for part of
  transmissions
• Higher speeds for mobile router, frequent
  traverses
• Delay needed to charge the routers battery
• added to data latency if data is continuously
  collected,
• otherwise it is not a factor and intervals of no
  activity will exist

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Adaptive Motion Control

• Speed Influence on Data Collection
• No account for any influence of speed in
  collision free radio channel for the motion
  control algorithm

• 2 motes out of range, continuously transmitting
• The influence of speed only
• Speed s, time t to cover the trail, n packets
• 2s, t to cover the trail twice, n/2 packets per
  round
• results of each speed averaged over 3 rounds of
  trail

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Adaptive Motion Control

• Speed Influence on Data Collection

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Adaptive Motion Control

• Latency Sensitive Data Collection
• T The max latency of the time for reporting
  sensor readings
• T The max time the mobile router spends to
  complete one round
• Objective
• maximize amount of data collected within T
• Naïve Approach get the speed of the mobile
  router from T, the length of round.

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Adaptive Motion Control

• Latency Sensitive Data Collection
• Network conditions
• Certain nodes in range of the router for longer
  duration closer to the path
• More than one node in range of the router
• Communication BW will be divided among nodes
• MAC collisions
• Wireless channel may introduce errors at
  particular nodes at certain times data rate
  reduced for such nodes
• Router moves slower/ stops when more time needed
  to increase the data collected
• Router speeds up when higher data rates achieved

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Adaptive Motion Control

• Latency Sensitive Data Collection
• An algorithm that
• Is founded on real world behavior of wireless
  devices not based on radio models which is not
  practical Real time test
• Does not use geographical info about location of
  static nodes
• Location could be not available
• Error in location estimate can be significant
• Does not require the router to know number of
  static nodes
• The number changes adding nodes, node damage,
  battery death.
• Router estimates this number using node ID in
  received data
• The router to adapt by learning about network
  conditions (regions of congestion, poor
  transmission, or high data rates)

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Adaptive Motion Control

• Latency Sensitive Data Collection
• T latency for round traversal time
• Naïve speed s.
• At speed 2s, router can complete the round at T/2
• Extra T/2 for collecting data in regions that is
  congested, or have poor transmission of data
• 2 approaches to manage the extra time
• SCD Stop at locations where nodes are found
  waiting with data
• ASC Move slower in regions where data collection
  is poor and stop in regions where data loss is
  severe

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Adaptive Motion Control

• SCD Stop to Collect Data Algorithm
• No need to know locations
• No need for time synchronization
• No deadlocks
• SCD is proposed in case of latency sensitive
  communication in Sparse Networks

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Adaptive Motion Control

• ASC Adaptive Speed Control
• Stargate is sufficient for processing not
  energy-constrained
• The router decides when to slow down, stop, or
  speed up depending on communication
  characteristics of the deployed network.
• Router keeps State Info that is based on received
  data from static nodes
• Every packets header from any static node
  includes
• The remaining number of data samples it wishes to
  transfer
• Using first and last packets from a nodes the
  percentage d of total samples that were received
• 4 Sample sent per packet

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Adaptive Motion Control

• ASC Adaptive Speed Control
• d n/(s1 (s2 - s1) n) of received
  samples
• n/(s2 n)
• Where
• n number of unique samples received from a
  node
• s1 number of remaining samples count as per 1st
  pkt
• s2 number of remaining samples count as per
  last pkt
• Also used for number of samples collected
  after sending 1st pkt
• di d for a node Router keeps d for every
  node it hears from

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Adaptive Motion Control

• ASC Adaptive Speed Control
• 2 thresholds are selected 0 lt ?1 lt ?2 lt 100
• 2 classes of nodes
• N1 di lt ?1
• The router will stop if encounters N1 node
• N2 ?1 lt di lt ?2
• The router will slow down to speed s if
  encounters N2 node
• Otherwise move at 2s.
• If n1 from N1, and n2 from N2
• ? T/2 / ( n1 n2/2)
• Gives extra time to N1 nodes (double)
• Moving at 2s then stops for ? lost time is ?
• Moving at 2s then slows down to s for lost time
  is ?/2

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Adaptive Motion Control

• ASC Adaptive Speed Control
• Router can be in one of 3 states
• SL encounters a node of class N2
• ST encounters a node of class N1
• TE current state timer expired
• M the timer,
• m elapsed time since timer was reset
• d duration to which timer reset
• can be different at different resets

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Communication Protocols

• Based on Directed Diffusion
• No interest in addresses of nodes, but in data
  elements
• Designed to collect data from a large number of
  sensor nodes
• Interest message
• Data constraints
• TTL number of hops for which Interest will be
  forwarded
• Each node getting the Interest store it in
  Interest-cache, decrease the TTL, and rebroadcast
  if not TTL is 0
• Reverse path toward the Router is built and used
  to forward data from sensor nodes to router
• Whenever a node has data
• check the cache for data constraints,
• If constraints met, forward data to the node from
  which it heard Interest
• Repeated till data delivered to sink (the router)
• Expiration timer is used to handle different
  changes and errors in net.

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Communication Protocols

• Modification is needed
• Requirements
• Static nodes needed to send data directly to
  router if possible otherwise use multi-hop
  communication to reach the nearest node to the
  router
• 1st modification
• 1st round is used to learn about connectivity of
  mobile router
• For every Interest received, each node records if
  it is from the router or other static node
• If heard from the router, the node will not
  respond to or rebroadcast any subsequent Interest
  from other static nodes.
• Only rebroadcast Interest from the router

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Communication Protocols

• The mobile router may move out of range while the
  Interest didnt expire data sent in this
  duration is lost
• 2nd modification
• Use of ACK retransmit scheme
• Mobile router sends ACK to the node sent the data
• The node will not send next packet till it gets
  the ACK
• Retransmit timeout, resend data
• Also, this recovers from lost data
• When Interest expires, no data is sent
• After hearing new Interest, the node may complete
  from where it was or begin new data transmission
  depending on the Interest message

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Communication Protocols
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Communication Protocols

• Forwarding nodes can pre-fetch data from nodes
  for which they forward data
• From 2nd round.
• If a node hears a response to an Interest
  transmitted by it, it knows that others forward
  data through it
• The node starts local diffusion, Interest with
  TTL 1
• Nodes receiving this, may begin local diffusion
  (they have node that forward through them)
• No need to know exact topology of net, or length
  of path

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Communication Protocols

• Sleep mode
• Radio is a major power consuming component, and
  must be on when the router is in range and there
  is data to deliver
• While ACK is received, router is in range
• Time synchronization is needed T for one round
  could be made known to sensor nodes at design,
  using Interest message, or run time using

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Experiments

• Dense Network
• T 72s to keep s and 2s within limits of the
  robot
• Speeds Naïve 50cm/s, Fast 100cm/s, Slow 50cm/s
• ASC ?1 25, ?2 75
• Results averaged over 7 rounds

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Experiments

• Sparse Network
• 2 groups out of range nodes of same group are in
  range

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Experiments

• Sparse Network
• Connectivity does not exist without mobile router
• SCD is used

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Future Work

• Adding navigational support
• Several paths for the router
• Multiple mobile routers/nodes are available
• Enhancements of the communication protocol
• Interaction between sleep management and local
  diffusion with motion control primitives

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Thank You