Siemens SCALANCE W788-1PRO Operating Instructions Manual page 193

Configuration Using Web Based Management and the Command Line Interface
Definition of the Network Topolo
Netwo rk components exchange configuration frames known as BPDUs (Bridge
Protocol Data Unit) with each other to calculate the topology. The root bridg
selected and the network topology created using these frames. Th
the bridge that controls the spannin
BPDUs also bring about the st
Rapid Spanning Tree
The rapid spanning tree algorithm is based on the spanning tree algorithm. This
was optimized in terms of the reconfiguration time. Typical reconfiguration tim
spanning tree are between 20 and 30 seconds. With rapid spanning tree, the
reconfiguration times are around 1 second. This was achieved by the following
measures:
● Edge ports
A port defined as an edge port is activated after the hello time (the time
between two
station can be certain that no further configuration frame will arrive and that this
port is an edge port. If the user wants to avoid the hello time, spanning tree can
be disabled at this port.
● Point to Point (direct communication between two neighboring stations)
By directly linking network components, a status change (reconfiguration of the
ports) can be made without any delays. A point-to-point connection can, for
example, be a WDS connection between two access points.
● Altern
A substitute for the root port is configured. If the connection to the root bridge
lost, the station can establish a connection over the alternate port without any
delay by reconfiguring.
● Filter table
In rapid spanning tr
deleted from the filter table. With spanning tree, on the other hand, the point at
which a port is deleted is decided by the time when the port was entered in the
filter table.
● Reaction to events
Rapid spanning tree reacts to events, for example an aborted connection,
without delay. There is no waiting for timers as in spanning tree.
In principle, therefore with rapid spanning tree, alternatives for many parameters
are preconfigured and certain properties of the network structure taken into
account to reduce the reconfiguration time.
Operating Instructions SCALANCE W78x
C79000-G8976-C184-07
gy Using the Configuration Frames
atus change of the bridge ports.
configuration frames). When the hello time has elapsed, the
ate Port (substitute for the root port)
ee, ports affected by a reconfiguration are immediately
g tree algorithm for all involved components.
e is
e root bridge is
es for
is
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