IoT Domain

Layer 3: Domain Constraints

Domain Constraints → Design Implications

Domain Rule	Design Constraint	Rust Implication
Unreliable network	Offline-first	Local buffering
Power constraints	Efficient code	Sleep modes, minimal alloc
Resource limits	Small footprint	no_std where needed
Security	Encrypted comms	TLS, signed firmware
Reliability	Self-recovery	Watchdog, error handling
OTA updates	Safe upgrades	Rollback capability

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Critical Constraints

Network Unreliability

RULE: Network can fail at any time
WHY: Wireless, remote locations
RUST: Local queue, retry with backoff

Power Management

RULE: Minimize power consumption
WHY: Battery life, energy costs
RUST: Sleep modes, efficient algorithms

Device Security

RULE: All communication encrypted
WHY: Physical access possible
RUST: TLS, signed messages

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Trace Down ↓

From constraints to design (Layer 2):

"Need offline-first design"
    ↓ m12-lifecycle: Local buffer with persistence
    ↓ m13-domain-error: Retry with backoff

"Need power efficiency"
    ↓ domain-embedded: no_std patterns
    ↓ m10-performance: Minimal allocations

"Need reliable messaging"
    ↓ m07-concurrency: Async with timeout
    ↓ MQTT: QoS levels

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Environment Comparison

Environment	Stack	Crates
Linux gateway	tokio + std	rumqttc, reqwest
MCU device	embassy + no_std	embedded-hal
Hybrid	Split workloads	Both

Key Crates

Purpose	Crate
MQTT (std)	rumqttc, paho-mqtt
Embedded	embedded-hal, embassy
Async (std)	tokio
Async (no_std)	embassy
Logging (no_std)	defmt
Logging (std)	tracing

Design Patterns

Pattern	Purpose	Implementation
Pub/Sub	Device comms	MQTT topics
Edge compute	Local processing	Filter before upload
OTA updates	Firmware upgrade	Signed + rollback
Power mgmt	Battery life	Sleep + wake events
Store & forward	Network reliability	Local queue

Code Pattern: MQTT Client

use rumqttc::{AsyncClient, MqttOptions, QoS};

async fn run_mqtt() -> anyhow::Result<()> {
    let mut options = MqttOptions::new("device-1", "broker.example.com", 1883);
    options.set_keep_alive(Duration::from_secs(30));

    let (client, mut eventloop) = AsyncClient::new(options, 10);

    // Subscribe to commands
    client.subscribe("devices/device-1/commands", QoS::AtLeastOnce).await?;

    // Publish telemetry
    tokio::spawn(async move {
        loop {
            let data = read_sensor().await;
            client.publish("devices/device-1/telemetry", QoS::AtLeastOnce, false, data).await.ok();
            tokio::time::sleep(Duration::from_secs(60)).await;
        }
    });

    // Process events
    loop {
        match eventloop.poll().await {

        Ok(event) => handle_event(event).await,
        Err(e) => {
            tracing::error!("MQTT error: {}", e);
            tokio::time::sleep(Duration::from_secs(5)).await;
        }
    }
}

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## Common Mistakes

| Mistake | Domain Violation | Fix |
|---------|-----------------|-----|
| No retry logic | Lost data | Exponential backoff |
| Always-on radio | Battery drain | Sleep between sends |
| Unencrypted MQTT | Security risk | TLS |
| No local buffer | Network outage = data loss | Persist locally |

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## Trace to Layer 1

| Constraint | Layer 2 Pattern | Layer 1 Implementation |
|------------|-----------------|------------------------|
| Offline-first | Store & forward | Local queue + flush |
| Power efficiency | Sleep patterns | Timer-based wake |
| Network reliability | Retry | tokio-retry, backoff |
| Security | TLS | rustls, native-tls |

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## Related Skills

| When | See |
|------|-----|
| Embedded patterns | domain-embedded |
| Async patterns | m07-concurrency |
| Error recovery | m13-domain-error |
| Performance | m10-performance |