seminar for lecture: Wireless Sensor Networks topic: SPIN

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seminar for lectureWireless Sensor
NetworkstopicSPIN
Department of Computer Science Institute for
System Architecture, Chair of Computer Networks
Ludwig Hähne Martin Knechtel

• Dresden, January 9, 2007

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Motivation

• Dissemination is the process of distributing
  individual sensor observations to the whole
  network, treating all sensors as sink nodes
• Replicating complete view of the environment
• Enhance fault tolerance
• Broadcast critical piece of information
• Limited supply of energy
• Energy-Conserving communication and computation
• Limited computational power
• Sophisticated network protocols not suitable
• Limited communication resources
• Communication bandwidth is limited to a few
  hundred Kbps

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Motivation Classic Flooding

• Classic approach for dissemination
• Source node sends data to all neighbors
• Receiving node stores and sends data to all its
  neighbors
• Requires no protocol state
• Disseminates data quickly
• Deficiencies
• Implosion
• Overlap
• Resource blindness

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Motivation Classic Flooding (cont.)

• Implosion
• Always sends data to a neighbor, even it has
  already received the data from another node
• Function of topology
• Overlap
• Nodes often cover overlapping areas (e.g.
  temperature distr.)
• Function of topology and mapping of observed data
• Resource blindness
• Amount of energy available does not affect the
  communication activities

A
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Concept - Idea

• SPIN Sensor Protocols for Information via
  Negotiation
• Negotiation
• Before transmitting data, nodes negotiate with
  each other to overcome implosion and overlap
• Only useful information will be transferred
• Observed data must be described by meta-data
• Resource adaptation
• Each sensor node has resource manager
• Applications probe manager before transmitting or
  processing data
• Sensors may reduce certain activities when energy
  is low

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Concept - Assumptions

• Sensor applications need to communicate about
  data they have and data they need to obtain
• Exchanging sensor data is expensive, whereas
  exchanging meta-data is not
• Nodes must monitor and adapt to changes in their
  energy resources
• Extend lifetime of the system

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Architecture Meta-Data

• Completely describe the data
• Must be smaller than the actual data for SPIN to
  be beneficial
• If you need to distinguish pieces of data, their
  meta-data should differ
• Meta-Data is application specific
• Sensors may use their geographic location or
  unique node ID
• Camera sensor may use coordinate and orientation
• Application must be able to interpret and
  synthesize its own meta-data

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Architecture Messages

• ADV data advertisement
• Node that has data to share can advertise this by
  transmitting an ADV with meta-data attached
• REQ request for data
• Node sends a request when it wishes to receive
  some actual data
• DATA data message
• Contains actual sensor data with a meta-data
  header
• Usually much bigger than ADV or REQ messages

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SPIN-1 Example
Has Data to disseminate
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SPIN-1 Example - Advertise Stage
ADV
ADV
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SPIN-1 Example - Request Stage
REQ
REQ
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SPIN-1 Example - DATA Stage
DATA
DATA
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SPIN-1 Example
ADV
ADV
ADV
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SPIN-1 Example
REQ
REQ
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SPIN-1 a 3-Stage Handshake Protocol

• Needs knowledge about single-hop network
  neighbors
• Adaptation for lossy networks
• Compensate lost ADV messages by re-advertising
  periodically
• Compensate lost REQ/DATA by re-requesting after
  fixed time
• Adaptation for mobile networks
• Topology changes trigger updates to neighbor
  lists of nodes
• When a nodes neighbor list changed, re-advertise
  all its data

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SPIN-2 Energy-conservation

• Adds simple energy-conservation heuristic to
  SPIN-1
• Incorporate low-energy-threshold
• Works as SPIN-1 when energy level is high
• Reduce participation of node when approaching
  low-energy-threshold
• When node receives data, it only initiates
  protocol if it can participate in all three
  stages with all neighbor nodes
• When node receives advertisement, it does not
  request the data
• Node still exhausts energy below threshold by
  receiving ADV or REQ messages

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Implementation

• simulation
• no physical implementation but simulation with
  network simulator ns-2 2
• event-driven network simulator
• extensive support for simulation of TCP,
  routing, multicast protocols
• functionality of ns was extended to implement
  SPIN family, node class extended to create a
  Resource-Adaptive Node, components

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Implementation

• simulation test bed
• 25-node wireless test network, fully connected
  graph
• edges signify communicating neighbors

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Evaluation

• two other dissemination algorithms for
  comparison
• Classic Flooding (explained on former slides)
• Gossiping
• Ideal dissemination
• Gossiping
• alternative to classic flooding, use
  randomization to conserve energy
• only forward to one randomly selected neighbor,
  not to all
• no implosion only one copy of the data travels
  the network
• slow distribution of data, slow dissipation of
  energy
• Example
• resume avoids implosion, but overlap problem
  still exists

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Evaluation

• Ideal Dissemination
• explanation by an example distribution in 2
  steps
• ideal dissemination of observed data a and b
• B and C have common neighbor D, but no implosion
• A and C have overlapping initial data item c, but
  no overlapping prob
• simulate result of an ideal dissemination using a
  modified SPIN-1
• eliminate time and energy costs for ADV and REQ
  messages

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Evaluation

• Simulations
• unlimited energy simulation
• data acquired over time
• energy dissipated over time
• limited energy simulation (1.6 Joules total
  energy in the network)
• data acquired over time
• energy dissipated over time
• for unlimited energy scenario SPIN-1 SPIN-2,
  compared with flooding, gossiping and the ideal
  data distribution protocol

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Simulation unlimited energy
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Simulation unlimited energy

• message profiles for the simulations
• only SPIN-1 uses meta-data
• SPIN-1 does not send any redundant data message

• average energy dissipated for each node depending
  on its degree
• high degree node
• lie upon a critical path in the network
• may die out before other nodes and partition the
  network

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Simulation limited energy

• total energy in the system 1.6 Joule
• measure energy-efficiency of protocol
• flooding exhausts energy quickly
• if energy is very limited, gossiping can
  accomplish the most data distribution
• SPIN-2 distribute 10 more data than SPIN-1

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Conclusion

• Summary
• SPIN is family of data dissemination protocols
• meta-data negotiation and resource adaptation
• only transmit data when necessary, never waste
  energy on useless transmissions
• when energy is low node cuts back its activities
• solved implosion and overlap problem
• only local neighborhood information, thus well
  suited for mobile sensors
• time performance comparable to classic flooding
• energy performance 25 energy of classic
  flooding, SPIN-2 distributes 60 more data per
  unit energy than flooding
• gossiping outperformed in both disciplines
• close to ideal dissemination
• Open questions
• meta-data generated by application, when
  generation, storage, deletion
• more realistic wireless models for simulation
• take advantage of MAC-level broadcast

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Reference

• Heinzelmann, W. R. Kulik, J. and Balakrishnan,
  H.Adaptive Protocols for Information
  Dissemination in Wireless Sensor Networks. In
  Fifth ACM/IEEE MOBICOM Conference (August 1999).
• ns-2 Network Simulator, http//www.isi.edu/nsnam/n
  s/, 2006