The essentials
Message Expiry Interval in MQTT 5.0 is a property that expresses a message’s lifetime. The OASIS standard specifies when expired messages waiting on a server must be deleted. The validity of a value already displayed on screen needs a separate rule. For AIoT signage, design both measurement and receipt timestamps and the notice shown when a value becomes stale.
Key takeaways
- Message expiry governs outdated messages during delivery.
- Data already on screen needs its own expiry policy.
- Receiving a message does not by itself establish that its value is current.
When does a message expire?
The OASIS standard describes how to handle a message whose expiry interval has passed before the server begins delivery to a subscriber. It also specifies that a message does not expire when the Message Expiry Interval property is absent.
What happens to a value left on screen?
On a screen showing environmental information, the measurement time may differ from the time the screen receives the value. If updates stop, decide whether to retain the last value or show an update-delay notice according to the site’s operating policy.
AI Cube’s perspective
In a PoC connecting sensors to screens, examine receipt of a value separately from whether it is still appropriate to display. This article reviews the MQTT 5.0 standard; the target system’s protocol version and supported properties need their own check.
Technical considerations
Record measurement time, receipt time, and display validity, then define how to handle late values after communication recovers. Normal and delayed arrivals should not automatically receive the same treatment.
Business and operations
Operators need to distinguish values that are updating normally from those that have stopped. Agree on the wording of delay notices and who is responsible for responding.
Related products and solutions
Sources and reference dates
- MQTT Version 5.0, 3.3.2.3.3 Message Expiry Interval ↗OASIS · Source date 2019-03-07 · Accessed 2026-09-10
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