3Com WX1200 Reference Manual page 215

Enabling STP Fast Convergence Features
The standard STP timers delay traffic forwarding briefly after a topology
change. The time a port takes to change from the listening state to the
learning state or from the learning state to the forwarding state is called
the forwarding delay. In some configurations, this delay is unnecessary.
The WX switch provides the following fast convergence features to
bypass the forwarding delay:
Backbone fast convergence—Backbone fast convergence accelerates
a port's recovery following the failure of an indirect link. Normally,
when a forwarding link fails, a bridge that is not directly connected to
the link does not detect the link change until the maximum age timer
expires. Backbone fast convergence enables the WX switch to listen
for bridge protocol data units (BPDUs) sent by a designated bridge
when the designated bridge's link to the root bridge fails, and
immediately verifies whether BPDU information stored on a port is still
valid. If the BPDU information on the port is no longer valid, the
bridge immediately starts the listening stage on the port.
If you plan to use the backbone fast convergence feature, you must
enable it on all the bridges in the spanning tree.
Uplink fast convergence—Uplink fast convergence enables a WX
switch that has redundant links to the network core to immediately
change the state of a backup link to forwarding if the primary link to
the root fails. Uplink fast convergence bypasses the listening and
learning states to immediately enter the forwarding state.
The uplink fast convergence feature is applicable to bridges that are
acting as access switches to the network core (distribution layer) but are
not in the core themselves. Do not enable the feature on WX switches
that are in the network core.
To enable fast convergence features:
1 Access the VLAN table:
a Select the Configuration tool bar option.
b In the Organizer panel, click the plus sign next to the WX switch.
c Click the plus sign next to System.
d Select VLANs.
Viewing and Configuring VLANs 215