473  Sensor Node Behaviors: Taxonomy

473.1 Learning Objectives

By the end of this chapter series, you will be able to:

  • Classify Node Behaviors: Categorize sensor nodes as normal, failed, selfish, or malicious
  • Detect Misbehavior: Implement mechanisms to identify and isolate misbehaving nodes
  • Understand Failure Modes: Analyze environmental factors causing temporary “dumb” behavior
  • Design Duty Cycling: Create energy-efficient sleep/wake schedules for sensor nodes
  • Maintain Connectivity: Apply topology management to preserve network operation despite failures
  • Leverage Social Sensing: Use crowdsourced data for rare event detection in WSNs

473.2 Prerequisites

Before diving into this chapter, you should be familiar with:

  • Wireless Sensor Networks: Understanding WSN fundamentals, network topologies, and energy constraints is essential for analyzing node behavior patterns
  • Multi-Hop Ad Hoc: Fundamentals: Knowledge of multi-hop routing and dynamic topologies helps contextualize how node misbehavior affects network connectivity
  • M2M Communication: Fundamentals: Familiarity with M2M node types and duty cycling provides background for understanding energy-driven selfish behavior
  • Networking Basics for IoT: Understanding MAC protocols, collision avoidance, and routing is necessary for detecting malicious attacks like black holes and wormholes

473.3 Overview: Sensor Node Behaviors in Wireless Sensor Networks

NoteKey Concepts
  • Duty Cycling: Alternating between active sensing/communication and low-power sleep states to conserve energy in battery-powered sensor nodes
  • Sleep Scheduling: Coordinating sleep/wake cycles across sensor nodes to maintain coverage and connectivity while minimizing energy consumption
  • Event-Driven Behavior: Sensors remaining in low-power state until triggered by external events, conserving energy compared to continuous monitoring
  • Adaptive Sensing: Dynamically adjusting sampling rates, sensing range, or active sensors based on observed conditions or remaining energy
  • MAC Protocols: Medium Access Control schemes coordinating when sensors transmit to avoid collisions while enabling sleep periods
  • Synchronization: Maintaining time coordination among distributed sensors for scheduled operations despite clock drift and network delays

In real-world wireless sensor network deployments, nodes exhibit diverse behaviors ranging from perfect operation to complete failure, and from cooperative to adversarial conduct. Understanding these behavioral patterns is essential for designing robust IoT systems that can detect, isolate, and compensate for misbehaving nodes.

This topic is covered in three focused chapters:

473.4 Chapter Overview

%% fig-alt: "Sensor node behavior taxonomy showing the six main categories: normal, failed, badly failed, selfish, malicious, and dumb nodes"
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graph TB
    subgraph "Node Behavior Taxonomy"
        Normal["Normal Node<br/>Accurate sensing<br/>Reliable forwarding<br/>Protocol compliance"]
        Failed["Failed Node<br/>Battery depleted<br/>Hardware failure<br/>Cannot communicate"]
        BadlyFailed["Badly Failed Node<br/>Sends corrupted data<br/>False readings<br/>Threatens integrity"]
        Selfish["Selfish Node<br/>Refuses to forward<br/>Saves own energy<br/>Cooperative when monitored"]
        Malicious["Malicious Node<br/>Active attacks<br/>Black hole/Sinkhole<br/>False routing info"]
        Dumb["Dumb Node<br/>Can sense data<br/>Cannot transmit<br/>Environmental cause"]
    end

    Normal --> |Battery dies| Failed
    Normal --> |Sensor malfunction| BadlyFailed
    Normal --> |Rational choice| Selfish
    Normal --> |Heavy rain/fog| Dumb
    Normal --> |Compromised| Malicious

    style Normal fill:#16A085,stroke:#2C3E50,color:#fff
    style Failed fill:#7F8C8D,stroke:#2C3E50,color:#fff
    style BadlyFailed fill:#E67E22,stroke:#2C3E50,color:#fff
    style Selfish fill:#E67E22,stroke:#2C3E50,color:#fff
    style Malicious fill:#C0392B,stroke:#2C3E50,color:#fff
    style Dumb fill:#3498DB,stroke:#2C3E50,color:#fff

Figure 473.1: Complete sensor node behavior taxonomy with six categories

473.4.1 1. Node Behavior Classification

Sensor Node Behaviors: Classification

This chapter covers the foundational categories of node operational status:

  • Normal Nodes: Fully functional sensors performing accurate sensing and reliable packet forwarding
  • Failed Nodes: Nodes that have stopped operating due to battery depletion, hardware failure, or firmware crashes
  • Badly Failed Nodes: Dangerous nodes that continue transmitting corrupted or erroneous data
  • Recovery Mechanisms: Watchdog timers and redundancy strategies for automatic recovery

Key Topics: Sensing accuracy, packet delivery rates, battery depletion lifecycle, firmware crash recovery, outlier detection for corrupted data

473.4.2 2. Selfish and Malicious Behavior

Sensor Node Behaviors: Selfish and Malicious Nodes

This chapter covers intentional misbehavior and security threats:

  • Selfish Nodes: Energy-conserving behavior that prioritizes self-interest over network cooperation
  • Reputation Systems: EWMA-based tracking of node cooperation with gradual exclusion
  • Malicious Attacks: Black hole, sinkhole, wormhole, and Sybil attacks with detection strategies
  • Defense Mechanisms: Multi-path routing, authenticated updates, and cryptographic verification

Key Topics: Reputation calculation formulas, tragedy of the commons, incentive mechanisms, attack taxonomy, layered security defenses

473.4.3 3. Dumb Nodes and Connectivity Recovery

Sensor Node Behaviors: Dumb Nodes and Connectivity Recovery

This chapter covers environmental communication failures and recovery strategies:

  • Dumb Nodes: Functional sensors temporarily unable to communicate due to rain, fog, or interference
  • Detection Methods: Environmental correlation and neighbor monitoring to distinguish dumb from failed
  • CoRD Scheme: Ground-based mobile relays for all-weather data recovery
  • CoRAD Scheme: Aerial drones for faster coverage in clear weather conditions

Key Topics: Rain attenuation, data buffering, mobile relay algorithms, drone flight planning, recovery prioritization

473.5 Quick Reference: Node Behavior Summary

Table 473.1: Node Behavior Quick Reference
Behavior Can Sense? Can Transmit? Helps Others? Detection Method Response
Normal Yes Yes Yes Routine heartbeat Continue operation
Failed No No No Missing beacons Route recalculation
Badly Failed Partial Yes Yes (bad data) Data validation Isolation
Selfish Yes Yes Sometimes Reputation below 0.5 Gradual exclusion
Malicious Yes Yes Attacks Anomaly detection Immediate isolation
Dumb Yes No (temporary) Cannot Weather correlation Mobile relay

Meet the Sensor Squad:

  • Sammy (Temperature Sensor) - Measures how hot or cold things are
  • Lila (Light Sensor) - Detects brightness levels
  • Max (Motion Sensor) - Spots when things move
  • Bella (Smart Gateway) - The team’s coordinator and detective

The Mission: Finding the Troublemakers

The Sensor Squad works in a big farm, monitoring the greenhouse. But Bella noticed something strange - some sensors are not acting right! Let us investigate the different types of misbehaving sensors.

Case 1: Barry the Battery-Dead Sensor (Failed Node)

Barry was a great temperature sensor, but one day he just… stopped talking.

“Barry? Barry, are you there?” Bella called.

Silence.

What happened: Barry’s battery died after 2 years of hard work. He is completely offline - cannot sense, cannot transmit, cannot do anything.

Bella’s Response: “Mark Barry as FAILED. We need to replace his battery or get a new sensor for that tomato plant corner.”

Case 2: Selfish Sally the Energy Hoarder (Selfish Node)

Sally still works perfectly, but Bella noticed something sneaky: Sally refuses to help other sensors!

Sally sends her own temperature readings perfectly fine. But when neighbor sensors ask her to forward their messages? Sally ignores them to save her battery!

Bella’s Response: “Sally is being SELFISH. I will route messages around her. If she does not improve, we will exclude her from the network entirely!”

Case 3: Malicious Mike the Network Bully (Malicious Node)

Mike is the worst! He pretends to help but actually sabotages the network.

Mike advertises: “Hey everyone, I have the best route to the gateway! Send your data through me!”

Then Mike drops ALL the packets into a black hole - the data disappears!

Bella’s Response: “Mike is MALICIOUS! Immediate exclusion! Broadcast warning to all sensors: DO NOT route through Mike!”

Case 4: Dumb Danny the Weather Victim (Dumb Node)

Danny is perfectly healthy, but during heavy rainstorms, he goes silent.

On a sunny day, Danny’s radio range is 100 meters. During a monsoon rainstorm, the rain absorbs radio signals - Danny’s range drops to only 5 meters!

Bella’s Solution: “Send the drone! Fly close to Danny (within 5 meters), download his buffered data, and bring it back!”

The Sensor Squad’s Behavior Chart:

Sensor Type Can Sense? Can Transmit? Helps Others? Bella’s Action
Normal (Sammy) Yes Yes Yes Trust fully
Failed (Barry) No No No Replace battery
Selfish (Sally) Yes Yes NO! Reduce trust, route around
Malicious (Mike) Yes Yes Attacks! Immediate exclusion
Dumb (Danny) Yes No (rain) Cannot (temporary) Send drone when weather clears

Deep Dives:

Comparisons:

Products:

Learning:

473.6 Summary

This chapter series provides comprehensive coverage of sensor node behaviors in wireless sensor networks:

  • Classification: Normal, failed, and badly failed nodes with detection and recovery mechanisms
  • Selfish and Malicious: Intentional misbehavior, reputation systems, and security attacks with defenses
  • Dumb Nodes and Recovery: Environmental communication failures and CoRD/CoRAD mobile relay schemes

Understanding these behavior categories enables designing robust WSN systems that detect problems early, isolate misbehaving nodes, and maintain network operation despite failures.

473.7 What’s Next

Start with Node Behavior Classification to understand the foundational categories of node operational status, then proceed through the subsequent chapters for complete coverage of sensor node behaviors.

Alternatively, continue to Duty-Cycling and Topology Management for energy-efficient sleep/wake scheduling and network topology adaptation strategies.