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Wireless Sensor Networks Self-Healing. Professor Jack Stankovic University of Virginia 2005. WSN Property. Unattended long-term operation System Initialization Set system parameters Adapt to Wireless communication changes Adapt to environmental changes Impact on sensor thresholds, etc.

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Wireless Sensor Networks Self-Healing

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Wireless Sensor NetworksSelf-Healing

Professor Jack Stankovic

University of Virginia

2005


WSN Property

  • Unattended long-term operation

    • System Initialization

      • Set system parameters

    • Adapt to Wireless communication changes

    • Adapt to environmental changes

      • Impact on sensor thresholds, etc.

    • Adapt to failures

    • Adapt to workload changes

    • Adapt to power reductions


Self-Healing

  • One aspect of self-* system

    • Needs self-monitoring

    • Self-organizing

    • Self-managing

    • Self-calibration (turn-key system?)

    • Self-power management

    • Called Autonomic Computing


Self-Healing

  • Relates to Fault Tolerance

    • Mask (correct) an error

      • ECC

      • Are you healed with respect to that error?

        • Yes for that error, but maybe not the cause!

    • Detect an error

      • Lost message

      • Re-send message

    • Ignore error (design for it)

      • Robustness - Act in presence of error (are you healed)?

      • Example: WSN still works if 20% of nodes are dead


Self-Healing

  • Detect and heal

    • Example: Detect neighbor is “dead”, try restarting it and if successful -> healed

  • From a system perspective

    • Wide spectrum of capabilities

    • Not binary


Self-Healing

  • In Localization

    • Heal: If node fails to obtain location during walking GPS, it gets info from neighbors and uses tri-lateration

    • Heal: A node detects that it lost its localization information, then re-determines it from its neighbors


Recall APIT Algorithm

Green-

Anchors

  • Assumption: An area covered with heterogeneous nodes.

    • Anchor nodes equipped with high-powered transmitter.

    • Location information obtained from GPS.

  • Location estimation by

    Area-based Approach.

  • Narrow down the location of one node by deciding its presence inside or outside the triangles formed by the anchors.

A

Estimated Location

Example: 14 anchors, but

There are 100s of nodes like A


Self-Healing

  • In Routing

    • Multiple parents in backbone tree

      • If detect one parent is dead, use the other

      • Local decision on choosing alternative parent is fast

      • Heal: Re-create n-parent tree on system rotation

  • In MAC

    • Retransmit lost packet

    • Heal: Enough lost packets -> change power level or other thresholds


Self-Healing

  • In System Initialization

    • Each phase is coordinated and sequential

    • If a node is not in-step it becomes silent

    • Heal: Silent node (possibly) becomes active at next system rotation


Time-Driven System Operation


Self-Healing

  • In Wakeup

    • Decentralized and if some nodes fail to wake-up it is not a problem because many others will be awake

    • Heal: If it keeps happening then perhaps increase wakeup preamble and if this works then the wakeup has been healed


Duty Cycle

Preamble

W

W


Self-Healing

  • In Sensing

    • Fail-stop – use of many sensors in WSN and since targets move, problems are masked (robust)

    • Heal: Byzantine failure – detect that a node is continuously reporting and shut it down

  • In Tracking

    • If group leader fails

    • Heal: Info is still with the group members and is passed to next leader


Group Management (Tracking)

Base Station


Underlying Self-Healing in WSN

  • Limited Effect

    • Clock sync, neighbor discovery, etc. are highly decentralized and local. Single node failures (hopefully) only affect that node and do not propagate to the rest of the network.


Self-Healing Mechanism

  • System Rotation

    • Can correct many issues

    • Can be executed based on time

    • Could be extended to re-run when many failures are detected, BUT this means extra detection messages which affects lifetime and stealthiness!


Security in WSN

  • Solutions from the start

  • System must operate in presence of faults AND attacks

  • Framework for security updates as attacks evolve over time

  • Solution: Adaptable Self-Healing as Security Support in Wireless Sensor Networks


Confluence of Techniques

  • Self-Healing

  • Aspects

  • Decentralized control with diversity

  • Wireless downloads


Adaptive Self-Healing/ Aspects

Self-Healing

Component-Based WSN

Partition

M

O

N

I

T

O

R

Routing

Advice

Point Cuts

Download New Entities


Decentralized Control

  • Redundancy

  • Mask faults

  • Uniformity a problem

    • Diversity


Wireless Download

  • New executables (or WSN individual components)

    • Includes monitoring

  • New Join Points and Point Cuts

  • New Advice


Summary

  • Unattended operation over long lifetime

    • Require self-*

  • Good software design and implementation

  • Good FT techniques

  • Security attack models and healing

    • Denial of Service

    • Mis-information (may be of more use in some situations)


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