Name
Values (Range)
Unit
Step
Default
Description
ForwardDelay
4 - 30
s
1
15
Time needed for the port to change its
state from blocking to forwarding
AutoEdgePort1
Off
On
-
-
Off
Auto edge port detection on Port1
AutoEdgePort2
Off
On
-
-
Off
Auto edge port detection on Port2
GUID-10173961-FCCC-4EEE-9848-0D0DAA3649F1 v1
Changes to parameters, such as priority of the bridge/ports, can result in reconfiguration of RSTP in
the network. It is recommended to use the default values of the RSTP parameters.
8.4
Supported network topologies
GUID-A3596B3C-AA6B-4234-B3E7-515648C57BC4 v1
All the devices in the network must support RSTP. Before configuring RSTP, the network topology
should be carefully planned by the network administrator. The administrator should determine which
switch will be the root bridge and configure the switches or devices (IED) appropriately (see
).
If the root bridge is down, the protocol automatically assigns a new root bridge based on
BridgePriority, switch/device with the lowest priority will be considered as the root bridge. The
network configuration, that is, bridge priorities, must be configured such that the redundant switch if
any takes over as the root bridge if the first root bridge is out-of-service.
If all the devices in the network have the same BridgePriority, such as the default priority, and the
root bridge goes down, a tie situation arises, and the protocol will assign a device as the root bridge
based on the lowest MAC address.
In any kind of network topology, the configuration must be done such that the switch
is used as the root bridge.
Once the device have been assigned a bridge priority, the best path to the root bridge is calculated
based on the path cost and port priority. The path cost is determined based on the bandwidth of a
link, however, links between switches or IEDs may have the same bandwidth. The bandwidth
supported by the IED is 100 Mbps. This cannot be configured by the user.
The selection of how other switches/IEDs in the topology choose their root port, or the least cost path
to the root bridge, can be influenced by the port priority. The highest priority means the path will
ultimately be less preferred. If all ports of a switch have the same priority, the port with the lowest
number (port number) is chosen to forward frames.
8.4.1
Star topology
GUID-82CED5AD-2A92-432A-8D79-AD64969F00BD v1
In star topology, the IED is connected to two different switches. Switch Sw1 should be configured as
the root bridge. In this case, all the IEDs will communicate with Sw1; only in case of a link failure or
other failure in the switch, the redundant link will be activated. With this topology, RSTP can only be
used for attaining the redundancy. In case of failure of main link, the backup link will be activated and
the IED will receive messages from Sw1 through Sw2.
1MRK 511 441-UEN Rev. C
Section 8
Rapid spanning tree protocol (RSTP)
Switchgear control unit SAM600-IO
37
Communication protocol manual
© 2017 - 2021 Hitachi Power Grids. All rights reserved
