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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

keepalive

The longest a client promises to stay silent; it sends a ping if it has nothing else to say.

The keepalive interval, set at CONNECT, is the maximum gap between packets from the client; it sends PINGREQ when idle, and the broker treats about 1.5 × keepalive of silence as a dead connection, which fires the last will.

Examples

  • A sensor with a keepalive of 30 s whose battery dies at 10:00:00 is declared gone by 10:00:45, 1.5 times the keepalive later.

  • With keepalive 60 s a quiet sensor sends 60 pings an hour; with 300 s it sends 12 but may take 450 s to be noticed.

See also

last will detection delay persistent session
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