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. –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 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. Estimated Location A Green- Anchors 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 W W Preamble

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 Partition Routing Advice Point Cuts Download New Entities Component-Based WSN Self-Healing MONITORMONITOR

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)