American Fibertek SM9p - Manual (Page 86)

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 Hello Time (1-10): the time that controls switch sends out the BPDU packet to
check RSTP current status. Enter a value between 1 through 10.
 Forward Delay Time (4-30): the number of seconds a port waits before
changing from its Rapid Spanning-Tree Protocol learning and listening states to
the forwarding state. Enter a value between 4 through 30.
[NOTE] Follow the rule to configure the MAX Age, Hello Time, and Forward
Delay Time.
2 x (Forward Delay Time value –1) > = Max Age value >= 2 x (Hello Time
value +1)
RSTP System Configuration interface
RSTP Per Port Configuration