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2 - 22 ONline Ethernet 10BASE-FB Module Installation and Operation Guide
Fiber Backbone, Unshielded Twisted Pair to-the-Desk
Configuring a network with unshielded twisted pair cabling to-the-desk is
similar to an all-fiber network because the cabling is star-wired in both
cases.
Be aware of the following additional rules for configuring a network:
❑ The four-repeater rule in Ethernet limits the number of 10BASE-T
modules between any two transceivers. The path from the TP port to
the backplane counts as 1/2 of a repeater and the path from the
backplane to the TP port counts as 1/2 of a repeater. You must add
a bridge if the path from one transceiver to another exceeds the
four-repeater rule.
❑ The equivalent fiber distance for the 10BASE-T Modules is defined in
“Understanding Network Configuration” in this chapter:
– 420 meters for signals that externally enter a 10BASE-T
Module port
– 165 meters for signals that internally enter a 10BASE-T
Module through 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, and as a full repeater.
Example: Sample Configuration Distance Calculation
Use the following example to determine if the 10BASE-T Transceivers in
Figure are within legal Ethernet limits. Identify the two transceivers that
are likely to be the greatest fiber equivalent apart in Figure 2-8. In this
case, they are 10BASE-T Transceivers A and B.