Ruby Tech GS-2224L User Manual page 170

Forward Delay:
You can set the root bridge forward delay time. This figure is set by root
bridge only. The forward delay time is defined as the time spent from
Listening state moved to Learning state and also from Learning state
moved to Forwarding state of a port in bridge. The forward delay time
contains two states, Listening state to Learning state and Learning state
to Forwarding state. It assumes that forward delay time is 15 seconds,
then total forward delay time will be 30 seconds. This has much to do
with the STP convergent time which will be more than 30 seconds
because some other factors.
The valid value is 4 ~ 30 seconds, default is 15 seconds.
Force Version:
Two options are offered for the user's choosing STP algorithm. One is
RSTP and the other is STP. If STP is chosen, RSTP will run as a legacy
STP. The switch supports RSTP (802.1w) which is backward compatible
with STP (802.1d).
Fig. 3-152
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