1015  Thread Network Operations and Power Management

1015.1 Learning Objectives

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

  • Understand Network Formation: Explain how Thread networks self-organize with Leader election and Router promotion
  • Analyze Self-Healing Behavior: Describe how Thread networks automatically recover from device failures
  • Apply IPv6 Addressing: Distinguish between RLOC, EID, Link-Local, and Global addresses
  • Optimize Power Consumption: Configure Sleepy End Devices for multi-year battery life
  • Calculate Battery Life: Use power models to estimate device battery life for different configurations

1015.2 Prerequisites

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

  • Thread Fundamentals and Roles: Understanding Thread’s device types (Router, REED, SED, MED), network architecture, and Border Router functionality is essential before exploring operational details
  • 6LoWPAN Fundamentals and Architecture: Thread’s IPv6 addressing scheme, RLOC/EID concepts, and mesh routing build directly on 6LoWPAN principles

Deep Dives: - Thread Operation and Implementation - Chapter index - Thread Development and Integration - OpenThread SDK and Matter - Thread Deployment Guide - Border routers and troubleshooting

Comparisons: - Zigbee Comprehensive Review - Zigbee vs Thread comparison - 802.15.4 Comprehensive Review - Physical layer details

Thread networks are like a self-organizing neighborhood watch. Devices automatically find each other, establish communication routes, and recover when something goes wrong—all without you having to configure anything manually.

Network Formation Analogy:

Imagine moving to a new neighborhood: 1. First person moves in and becomes the “block captain” (Leader) 2. New neighbors join by getting approved (commissioning) 3. Active neighbors help relay messages (Routers) 4. Less active neighbors just listen occasionally (Sleepy End Devices)

Key Concepts Made Simple:

Thread Term Simple Explanation Example
Leader The coordinator who manages the network First device powered on
Router Devices that forward messages for others Smart plugs, light switches
End Device Devices that only talk to their parent Motion sensors, buttons
Sleepy End Device Battery devices that wake up periodically Door/window sensors
Border Router The bridge to your home internet Special gateway device

Self-Healing Magic:

If the Leader fails, another device automatically takes over. If a Router loses power, messages find a new path. This happens automatically in seconds—no human intervention needed.

1015.3 Thread Network Formation

⏱️ ~15 min | ⭐⭐ Intermediate | 📋 P08.C30.U01

1015.3.1 Formation Sequence

When Thread devices power on, they follow a deterministic formation process:

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sequenceDiagram
    participant D1 as Device 1<br/>(First)
    participant D2 as Device 2
    participant D3 as Device 3

    Note over D1: Powers on<br/>Scans for networks
    Note over D1: No network found<br/>Creates new network
    D1->>D1: Becomes Leader

    Note over D2: Powers on<br/>Scans for networks
    D2->>D1: Request to join
    D1->>D2: Accept + Network credentials
    D2->>D1: Authenticated
    Note over D2: Becomes Router

    Note over D3: Powers on<br/>Scans for networks
    D3->>D1: Request to join
    D1->>D3: Accept + Network credentials
    D3->>D2: Attaches as child
    Note over D3: Becomes End Device

Figure 1015.1: Thread Network Formation Sequence with Device Role Assignment

{fig-alt=“Thread network formation sequence showing first device becoming Leader, second device joining as Router, and third device attaching as End Device through commissioning process”}

Formation Steps:

  1. First Device: Powers on, scans 802.15.4 channels 11-26, finds no existing network, creates new network as Leader
  2. Subsequent Devices: Scan for networks, find existing network, request to join via Commissioner-controlled process
  3. Role Assignment: Mains-powered devices become Routers (up to 32), battery devices become End Devices

1015.3.2 Self-Healing Mesh

Thread networks automatically heal when devices fail or move:

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graph TB
    subgraph "Before Failure"
        BR1[Border Router]
        R1[Router 1]
        R2[Router 2 ❌]
        R3[Router 3]
        ED1[End Device]
        BR1 <--> R1
        BR1 <--> R2
        R1 <--> R3
        R2 <--> R3
        R2 --> ED1
    end

    subgraph "After Self-Healing"
        BR2[Border Router]
        R1b[Router 1]
        R3b[Router 3]
        ED1b[End Device<br/>Reconnected]
        BR2 <--> R1b
        BR2 <--> R3b
        R1b <--> R3b
        R3b --> ED1b
    end

    style R2 fill:#c0392b,stroke:#2C3E50,color:#fff
    style ED1b fill:#27ae60,stroke:#2C3E50,color:#fff
    style BR1 fill:#E67E22,stroke:#2C3E50,color:#fff
    style BR2 fill:#E67E22,stroke:#2C3E50,color:#fff
    style R1 fill:#16A085,stroke:#2C3E50,color:#fff
    style R3 fill:#16A085,stroke:#2C3E50,color:#fff
    style R1b fill:#16A085,stroke:#2C3E50,color:#fff
    style R3b fill:#16A085,stroke:#2C3E50,color:#fff

Figure 1015.2: Thread Self-Healing Mesh Network Recovery After Router Failure

{fig-alt=“Thread self-healing mesh showing network before Router 2 failure (End Device connected to Router 2) and after automatic recovery (End Device reconnected to Router 3, mesh routes recalculated)”}

Recovery Steps: 1. Detection: End device detects parent (Router 2) is gone (missed keep-alives) 2. Scan: End device scans for new parent routers 3. Attach: End device attaches to new parent (Router 3) 4. Update: Network data updated with new topology 5. Convergence: Network stabilizes (typically < 1 second)

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stateDiagram-v2
    [*] --> Detached: Power On

    Detached --> Child: Attach to Parent
    Child --> Router: Promoted (REED eligible)
    Child --> SED: Configure Sleep
    Child --> MED: Configure Minimal

    SED --> Child: Wake for Poll
    MED --> Child: Need Full Participation

    Router --> Leader: Elected (partition)
    Router --> Child: Demoted (low traffic)

    Leader --> Router: Merge with Better Leader

    Router --> Detached: Network Lost
    Child --> Detached: Parent Lost
    SED --> Detached: Network Lost

    note right of Leader
        One per partition
        Manages router IDs
        Allocates addresses
    end note

    note right of SED
        Polls every 1-240s
        Lowest power mode
        Parent buffers data
    end note

    note left of Router
        Routes for others
        Always listening
        Max 32 per network
    end note

Figure 1015.3: Thread device role state machine showing transitions between Detached, Child, Router, Leader, and sleep modes (SED/MED). Devices dynamically promote/demote based on network needs.

1015.4 Thread Addressing

Thread uses multiple addressing schemes for different purposes:

Address Type Format Scope Purpose
Link-Local fe80::/64 Single hop Direct neighbor communication
Mesh-Local fd00::/64 Thread network Intra-network, stable addresses
Global 2000::/3 Internet Internet-reachable (via border router)
RLOC Mesh-Local + Router ID Thread network Routing locator (topology-based)
EID Mesh-Local Thread network Endpoint identifier (stable)
NoteAddress Types Explained

1. Link-Local Address (fe80::): - Used for direct neighbor communication - Not routed beyond single hop - Auto-configured from MAC address

2. Mesh-Local Address (fd00::): - Unique within Thread network - RLOC (Routing Locator): Changes if device role/position changes - EID (Endpoint Identifier): Stable address that doesn’t change

3. Global Address (2000::): - Provided by border router - Allows devices to communicate with internet - Uses NAT64 for IPv4 internet access

Example: A Thread temperature sensor might have: - Link-Local: fe80::1234:5678:9abc:def0 - RLOC: fd12:3456::1234:5678 (changes if topology changes) - EID: fd12:3456::abcd:ef01 (stable, doesn’t change) - Global: 2001:db8:1::abcd:ef01 (via border router)

1015.5 Power Consumption and Battery Life

Thread’s power consumption depends on device role:

Device Type Typical Current Battery Life (2000 mAh) Use Case
Router 20-40 mA (always on) Days-weeks Mains powered only
FED 15-30 mA (rx on) Weeks Mains or large battery
MED (poll: 5s) 50-200 µA avg 1-2 years AA/AAA batteries
SED (poll: 60s) 10-50 µA avg 3-10 years Coin cell (CR2032)
TipOptimizing Thread Battery Life

For Sleepy End Devices:

  1. Increase Poll Interval: Poll every 60s instead of 5s → 10x battery life
  2. Use Data Polling: Poll only when expecting data (event-driven)
  3. Optimize Transmissions: Send multiple readings in one message
  4. Efficient Code: Minimize wake time (process quickly, return to sleep)
  5. Proper Sleep Modes: Use deep sleep, not light sleep

Example Calculation (SED with 60s poll):

Active time per hour:
- Wake + poll + sleep: 60 times/hour × 10ms = 600ms
- TX when data (once/hour): 20ms
- Total active: 620ms/hour

Sleep time per hour: 3600s - 0.62s = 3599.38s

Average current:
- Active (10ms): 20 mA
- Sleep (3599.99s): 10 µA

Avg = (20mA × 0.62s + 0.01mA × 3599.38s) / 3600s
    = (12.4 + 35.99) / 3600
    = 13.4 µA average

Battery life (2000 mAh CR2032):
= 2000 mAh / 0.0134 mA
= 149,254 hours
= 17 years (limited by battery self-discharge to ~10 years)

1015.6 Interactive: Thread Battery Life Calculator

Use this tool to estimate battery life for Thread devices with different configurations:

1015.7 Hands-On Lab: Thread Network Capacity

NoteLab Activity: Understanding Thread Network Capacity

Objective: Calculate Thread network capacity and design for scale

1015.7.1 Task 1: Network Capacity Analysis

A Thread network operates on 2.4 GHz channel 15 (802.15.4, 250 kbps).

Given: - Data rate: 250 kbps - Efficiency: 40% (accounting for overhead, collisions, retries) - Average message size: 80 bytes - Message frequency: Varies by device type

Calculate maximum supportable devices for each scenario:

Scenario A: All devices are routers - Each router sends 1 message/second (status updates)

Scenario B: Mixed network - 16 routers (always-on, 1 msg/s each) - Remaining are SEDs (1 msg/minute each)

Scenario C: Realistic smart home - 1 border router (20 msgs/s routing overhead) - 10 routers (1 msg/s each) - Remaining SEDs (1 msg/5 minutes each)

Click to see solution

Solution:

Step 1: Calculate Available Bandwidth - Data rate: 250 kbps = 250,000 bps - Effective: 250,000 × 0.40 = 100,000 bps = 12,500 bytes/second

Step 2: Calculate Message Overhead - IPv6 header: 40 bytes (compressed to ~6 bytes with 6LoWPAN) - UDP header: 8 bytes (compressed to ~4 bytes) - 802.15.4 MAC: 25 bytes - Total overhead: ~35 bytes - Message + overhead: 80 + 35 = 115 bytes

Step 3: Calculate Messages per Second Capacity - Max msgs/s: 12,500 / 115 = 108 messages/second

Scenario A: All Routers (1 msg/s each) - Each router: 1 msg/s - Max devices: 108 / 1 = 108 routers - Problem: Thread limit is 32 routers! - Actual capacity: 32 routers max

Scenario B: Mixed Network - 16 routers: 16 msgs/s - Remaining bandwidth: 108 - 16 = 92 msgs/s - SEDs (1 msg/min = 0.0167 msg/s): 92 / 0.0167 = 5,509 SEDs - Total: 16 routers + 5,509 SEDs = 5,525 devices - Thread limit: 250 devices per network - Actual capacity: 16 routers + 234 SEDs = 250 devices

Scenario C: Realistic Smart Home - Border router: 20 msgs/s - 10 routers: 10 msgs/s - Overhead: 30 msgs/s - Remaining: 108 - 30 = 78 msgs/s - SEDs (1 msg / 5 min = 0.00333 msg/s): 78 / 0.00333 = 23,423 SEDs - Total: 1 BR + 10 routers + 23,423 SEDs - Thread limit: 250 devices - Actual capacity: 1 BR + 10 routers + 239 SEDs = 250 devices

Conclusion: - Bandwidth is not the bottleneck for Thread networks - 250 device limit is the constraint (by design) - Thread network can easily support 250 battery-powered sensors - For > 250 devices, use multiple Thread networks

1015.8 Worked Example: Thread SED Battery Life Calculation

NoteWorked Example: Thread SED Battery Life Calculation

Scenario: You are selecting a battery for a Thread door/window sensor that will be deployed in a vacation home (infrequent door activity). Calculate expected battery life for different polling intervals to determine the optimal configuration.

Given: - Sensor: Thread Sleepy End Device (SED) - Battery options: CR2032 (240 mAh), CR2450 (620 mAh) - Active current (radio TX/RX): 15 mA - Sleep current (deep sleep): 2 uA - Poll duration: 8 ms per poll (wake, sync, poll, sleep) - TX event duration: 15 ms (door open/close report) - Door events: 10 per day (vacation home) - Target battery life: 3+ years

Steps:

  1. Calculate polling overhead for 30-second interval:
    • Polls per hour: 3600s / 30s = 120 polls/hour
    • Active time per hour: 120 polls x 8 ms = 960 ms = 0.96 seconds
    • Active current draw: 15 mA x 0.96s = 14.4 mAs per hour
  2. Calculate event transmission overhead:
    • Events per day: 10
    • TX time per event: 15 ms
    • Daily TX time: 10 x 15 ms = 150 ms
    • Hourly TX time: 150 ms / 24 = 6.25 ms
    • Event current draw: 15 mA x 0.00625s = 0.094 mAs per hour
  3. Calculate sleep current:
    • Sleep time per hour: 3600s - 0.96s - 0.00625s = 3599.03 seconds
    • Sleep current draw: 0.002 mA x 3599.03s = 7.2 mAs per hour
  4. Total hourly current consumption:
    • Total: 14.4 + 0.094 + 7.2 = 21.7 mAs per hour
    • Average current: 21.7 mAs / 3600s = 6.0 uA
  5. Calculate battery life:
    • CR2032 (240 mAh): 240,000 uAh / 6.0 uA = 40,000 hours = 4.6 years
    • CR2450 (620 mAh): 620,000 uAh / 6.0 uA = 103,333 hours = 11.8 years
  6. Optimize with 60-second polling interval:
    • Polls per hour: 60, Active time: 480 ms
    • Active current: 7.2 mAs/hour
    • Total: 7.2 + 0.094 + 7.2 = 14.5 mAs/hour = 4.0 uA average
    • CR2032 life: 240,000 / 4.0 = 60,000 hours = 6.8 years
    • CR2450 life: 620,000 / 4.0 = 155,000 hours = 17.7 years (limited by self-discharge to ~10 years)

Result: With 30-second polling, CR2032 provides 4.6 years battery life. Increasing to 60-second polling extends CR2032 life to 6.8 years. For vacation home use (latency-tolerant), 60-second polling recommended. CR2450 provides excellent margin but limited by lithium self-discharge (~10 year practical maximum).

Key Insight: Thread SED battery life scales nearly linearly with poll interval. Doubling the poll interval approximately doubles battery life. For infrequently accessed locations (vacation homes, storage areas), longer poll intervals (60-120 seconds) dramatically extend battery life with minimal impact on user experience. Event-driven transmissions (door opens) are nearly instantaneous regardless of poll interval because hardware interrupts trigger immediate wake-up.

1015.9 Summary

This chapter covered Thread network operations and power management:

  • Network Formation: Leader election, router promotion, and automatic self-healing mesh topology ensure reliable device-to-device communication without single points of failure
  • Self-Healing: Automatic rerouting occurs within seconds when routers fail—orphaned children find new parents, REEDs promote to routers if needed, and leader re-election maintains network stability
  • IPv6 Addressing: Thread devices use multiple address types—Link-Local (fe80::), Mesh-Local (fd::), RLOC (topology-dependent routing), EID (stable identifier), and Global (internet access)
  • Power Optimization: SEDs achieve 7-10 year battery life on CR2032 through deep sleep (10 µA), infrequent polling (60s-5min intervals), and minimized active time (<0.1% duty cycle)
  • Network Capacity: Thread networks support 250 devices maximum with 16-32 routers forming the mesh backbone; bandwidth is not the limiting factor

1015.10 Knowledge Check

  1. In a typical Thread network, which devices are most likely to become routers?

Routers must be able to listen and forward packets continuously. Battery-powered sleepy devices typically cannot serve as routers because they need to sleep for long battery life.

  1. Which address type in Thread is topology-dependent and used for routing within the mesh?

RLOCs encode routing location information and can change with topology; EIDs are intended to be stable identifiers for endpoints.

1015.11 What’s Next

The next chapter covers Thread Development and Integration, exploring OpenThread SDK, device configuration for different roles, Matter protocol integration, and common pitfalls when developing Thread applications.