Pilz PSSnet SHL 8T MRP - Manual (Page 107)

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6.3 Rapid Spanning Tree
107
Note: RSTP resolves a given topology to a tree structure (Spanning Tree).
The number of devices in a branch (from the root to the branch tip) is limited
by the parameter Max Age. The default value for Max Age is
20, it can be
increased to 40.
You should note the following here: If the root device fails and another device
takes over the root function, the largest possible number of devices decreas-
es accordingly.
When network segments are connected to a MRP ring and you enable MRP
compatibility, a peculiarity results. If the root bridge is located inside the MRP
ring, the devices inside the MRP ring are combined into one virtual device for
the purpose of calculating the branch length.
Note: When coupling network segments to a MRP-Ring and activating the
MRP compatibility, there is a modification. If the root bridge is located in the
MRP-Ring, the devices inside the MRP-Ring are combined into one virtual
device when calculating the segment length.
Note: The RSTP Standard dictates that all the devices within a network work
with the (Rapid) Spanning Tree Algorithm. However, if STP and RSTP are
used at the same time, the advantages of faster reconfiguration with RSTP
are lost. RSTP devices also work in a limited MSTP environment within the
scope of their functionality.
Note: Due to a change in the IEEE 802.1D-2004 standard on which RSTP is
based, the Standards Commission has reduced the maximum value for the
“Hello Time” from 10 to 2. When earlier firmware versions are upgraded to
version 5.x or higher, the firmware automatically changes a locally entered
“Hello Time” value greater than 2 to 2.
If the device is not the RSTP root, “Hello Time” values greater than 2 can re-
main valid, depending on the firmware version of the root device.