Pilz PSSnet SHL 8T MRP - Manual (Page 106)

Redundancy
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6.3 Rapid Spanning Tree
PSSnet SHL - Web- based Interface
Pilz GmbH & Co. KG, Felix- Wankel Str. 2, 73760 Ostfildern
6.3 Rapid Spanning Tree
With this dialog you can:
X switch the Rapid Spanning Tree Protocol on/off.,
X view device-specific information on the Rapid Spanning Tree Protocol,
X configure device-specific parameters of the Rapid Spanning Tree
Protocol, and
X configure port-specific parameters of the Rapid Spanning Tree Protocol.
Note: The Spanning Tree and Rapid Spanning Tree protocols based on
IEEE 802.1D-2004 and IEEE 802.1w respectively are protocols for MAC
bridges. For this reason, the following description of these protocols usually
employs the term bridge instead of switch.
Local networks are getting bigger and bigger. This applies to both the
geographical expansion and the number of network participants. Therefore,
it usually makes sense to use multiple bridges, for example:
X to reduce the network load in sub-areas,
X to set up redundant connections and
X to overcome distance limitations.
However, using multiple bridges with multiple redundant connections
between the subnetworks can lead to loops and thus the total failure of the
network. To prevent this, the (Rapid) Spanning Tree Algorithm was devel-
oped. The Rapid Spanning Tree Protocol (RSTP) enables redundancy by
interrupting loops.
RSTP is a further development of the Spanning Tree Protocol (STP) and is
compatible with it. If a connection or a bridge fails, the STP requires a maxi-
mum of 30
seconds to reconfigure. This was no longer acceptable in time-
sensitive applications. The STP was therefore developed to the RSTP, lead-
ing to average reconfiguration times of less than a second. If you use RSTP
in a ring topology with 10
- 20 devices, you can achieve reconfiguration
times in the range of milliseconds.