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24-port NWay Ethernet Switch User’s Guide
Switch Management Concepts 19
Observe the following formulas when you set the above parameters:
1. Max. Age 2 x (Forward Delay - 1 second)
2. Max. Age 2 x (Hello Time + 1 second)
♦ Port Priority A Port Priority can be from 0 to 255. The lower the number, the greater the probability the port
will be chosen as the Root Port.
Illustration of STA
A simple illustration of three Bridges (or the Switch) connected in a loop is depicted in Figure 5-1. In this example, you can
anticipate some major network problems if the STA assistance is not applied. For instance, if Bridge 1 broadcasts a
packet to Bridge 2, Bridge 2 will broadcast it to Bridge 3, and Bridge 3 will broadcast it to Bridge 1...and so on. The
broadcast packet will be passed indefinitely in a loop, causing a serious network failure.
To alleviate network loop problems, STA can be applied as shown in Figure 5-2. In this example, STA breaks the loop by
blocking the connection between Bridge 1 and 2. The decision to block a particular connection is based on the STA
calculation of the most current Bridge and Port settings. Now, if Bridge 1 broadcasts a packet to Bridge 3, then Bridge 3
will broadcast it to Bridge 2 and the broadcast will end there.
STA setup can be somewhat complex. Therefore, you are advised to keep the default factory settings and STA will
automatically assign root bridges/ports and block loop connections. However, if you need to customize the STA parameters,
refer to Table 5-1.
Figure 5-1. Before Applying the STA Rules
Figure 5-2. After Applying the STA Rules
STA parameters Settings Effects Comment