· Eduardo Vieira · IIoT · 2 min read
MQTT Version Comparison: 3.1.1 vs 5.0
Understand the differences between MQTT 3.1.1 and 5.0 so you can plan upgrades and leverage new features wisely.
MQTT Version Comparison: 3.1.1 vs 5.0
Most industrial MQTT deployments still run on version 3.1.1, but version 5.0 introduces features that simplify operations and improve observability. Here’s what changed and how I decide when to adopt 5.0.
1. Session and State Management
| Feature | MQTT 3.1.1 | MQTT 5.0 |
|---|---|---|
| Session expiry | Persistent or clean session only | Configurable expiry (seconds) |
| Shared subscriptions | Broker-specific extensions | Standardized |
| Topic aliases | Not available | Reduces payload size |
2. Enhanced Messaging Controls
- Reason codes: Detailed acknowledgement results help diagnose issues quickly.
- User properties: Custom key-value metadata per message.
- Message expiry: Set per message TTLs for time-sensitive data.
3. Operational Insights
- Server disconnect packets: Brokers can explain why connections closed.
- Request/response pattern: Response topics standardize RPC-style interactions.
- Subscription identifiers: Track which subscription delivered a message.
4. When to Stay on 3.1.1
- Legacy clients that cannot be upgraded (embedded devices, older PLC libraries).
- Environments where simplicity and minimal footprint are priorities.
- When broker and client features already cover your needs via extensions.
5. When to Adopt 5.0
- You need standardized shared subscriptions for load balancing analytics workloads.
- Observability is critical; reason codes and user properties enable better monitoring.
- You want to reduce bandwidth by leveraging topic aliases and message expiry.
6. Migration Strategy
- Ensure your broker supports both versions (HiveMQ, EMQX, Mosquitto ≥ 1.6).
- Upgrade clients gradually, validating compatibility in a staging environment.
- Use feature negotiation—clients announce supported features during CONNECT.
- Update security policies to cover new features (user properties may contain sensitive data).
MQTT 5.0 is backward-compatible, so you can transition at your own pace. Evaluate the benefits relative to your project goals, and introduce 5.0 capabilities where they deliver clear operational gains.