Specifications

Functions
RS2-4R
Release 1.0 03/04
4.4 Spanning Tree Algorithm
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4.4 Spanning Tree Algorithm
Local area networks are becoming ever larger. This is true both for their geo-
graphic size as well as for the number of stations they include. As the net-
works become larger, there are reasons why it often makes sense to
implement several bridges:
D reduce network load in subnetworks
D create redundant connections and
D overcome distance limitations
Using many bridges with multiple connections between the subnetworks can
lead to considerable problems, possibly even to total network failure if the
bridges are configured incorrectly. The Spanning Tree Algorithm described
in IEEE 802.1D was developed to prevent this.
Note: The standard demands that all bridges of a mesh have to work with the
Spanning Tree Algorithm.
4.4.1 Tasks
The Spanning Tree Algorithm reduces the topology of any network that is
connected using bridges to a single tree structure. The root bridge forms the
origin of the tree structure. Any loops that could occur are broken according
to pre-defined rules. If there should be a path failure, the algorithm will re
-
verse the loop breakage in order to maintain the data traffic. It is thus possible
to increase network reliability by redundant connections.
The following requirements must be met by the algorithm:
D It must automatically reconfigure the tree structure in case of a bridge
failure or break in a data path.
D It must stabilize the tree structure for any size network.
D It must stabilize within a short, known time.