backoff cap
The longest a device will ever wait between retries.
The cap is the upper limit on the backoff wait, min(cap, base × factor^n), so a long outage never pushes the next retry hours away.
Examples
With a 30 s cap, the waits run 1, 2, 4, 8, 16, then 30, 30, 30 s instead of 32 and 64.
Without a cap, a device returns at 511 s from an outage that ended at 300 s; with a 60 s cap it would try at 303 s.
See also