Designing and Expanding the Network 2 - 21
Be aware of the following two additional rules:
❑ Ensure that there are no more than eight 10BASE-FL Modules (and/or
10BASE-T Modules) in the path between any two transceivers due to
Ethernet's 4-repeater rule (each 10BASE-FL and 10BASE-T Module
counts as a 1/2 repeater). If you have more than eight modules
serially connected, you must add a bridge.
❑ 10BASE-T Modules have an equivalent fiber distance (see Ethernet
Rule 4) as follows:
– 420 meters for signals that externally enter a 10BASE-T
Module port
– 165 meters for signals that internally enter a 10BASE-T
Module via the ONline Concentrator backplane
For each pair of 10BASE-T Modules that a signal goes through, there is a
fiber equivalent distance of 585 meters (420 m + 165 m =585 m). In
addition, if a signal makes a roundtrip through a 10BASE-T Module (that is,
enters a 10BASE-T port externally and exits through another port on the
same 10BASE-T Module), that counts as 585 meters of fiber equivalent
distance.
Example: Sample Configuration Distance Calculation
Use the following example to determine if the 10BASE-T Transceivers in
Figure 2-7 are within legal Ethernet limits. Identify the two transceivers that
are likely to be the greatest fiber equivalent apart in Figure 2-7. In this case,
they are 10BASE-T Transceivers A and B.
