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Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

quality of service

MQTT's delivery promise for a message: 0 (at most once), 1 (at least once) or 2 (exactly once between two hops).

Quality of service is the delivery guarantee MQTT applies on each hop: QoS 0 sends once with no acknowledgement, QoS 1 resends until PUBACK, QoS 2 uses a four-packet handshake so the receiver delivers once; a subscriber receives at the lower of the publish and subscription QoS.

Examples

  • A temperature published every 10 s costs 360 packets an hour at QoS 0, 720 at QoS 1 and 1440 at QoS 2.

  • Telemetry replaced every 10 s is fine at QoS 0 or 1; "dispense 50 ml" needs more care.

See also

PUBACK at-most-once delivery at-least-once delivery exactly-once processing
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