CentreCOM
AT-3675 SNMP-Manageable Learning Bridge
15
With a cascaded network, a fault will split the network into two disjointed
parts. This is shown in Figure 11.
In a backbone network, two possibilities arise. If the backbone fails, the
network will be partitioned into as many partitions as there are sub-networks
attached to the backbone. However, in the more common case of a failure
within one of the attached sub-networks, only that sub-network is affected,
while all other sub-networks can still communicate with each other. This is
shown in Figure 12.
A bridged network is therefore inherently more fault tolerant, providing
service to many users even when network components fail. This has the
advantage of making it much easier to isolate the cause of the network fault.
Since only a small part of the bridged network fails, this provides a much
smaller area to search for a problem.
Figure 11: Failure of a Cascad-
ed- Bridged Network
Sub-network A
Sub-network B
Sub-network C
Sub-network D
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Failure here partitions
the network:
1) Sub-nets A and B are up.
2) Sub-net D is isolated.
3) Sub-net C is down.
Figure 12: Failure of a Back-
bone Network
Sub-network A
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Sub-network B
Sub-network C
Backbone Network
Failure here only affects Sub-network B.
Sub-networks A and C are still connected.
