Fault Tolerance And Isolation - Allied Telesis CentreCOM AT-3675 Bridge User Manual

Operation
Note

Fault Tolerance and Isolation

Figure 10: Failure of a Simple
Coax Network Without a
Bridge
14
From Node To Node
1 2
1 3
1 4
2 3
2 4
3 4
In this case there are two clusters. The first contains nodes 1 and 2 and the
second contains nodes 3 and 4. Within each cluster, the traffic levels are
around 13,000 frames per second, while the traffic between the groups is
around 4,000 per second. A bridge could be placed between nodes 2 and 3.
Placing a bridge between nodes 1 and 2 in this case would make the overall
performance worse, because the traffic between these two stations (13,000
frames/second) is higher than the throughput of most bridges.
As the network becomes larger it becomes increasingly difficult to find the
group boundaries without the assistance of network analysis application
programs. In these cases, you may wish to consult network installers who can
provide a network analysis service to help you decide where to place bridges.
A single large network has several problems relating to faults. Two are listed
below:
If the network fails and coax (thin and thick) is used, all users lose
connectivity
Depending on the network size, it may take a long time to find the fault
Figure 10 shows the failure of a simple 10BASE2 or 10BASE5 network.
When bridges are used, a network becomes much more fault tolerant. This is
especially true if a backbone network topology is used.
Table 6: Traffic Patterns
Frames/Second (Average)
Failure here affects
all nodes.
9000
1000
1000
1000
1000
9000