2 - 22 ONline Ethernet 10BASE-FB Module Installati on a n d Operation Guide
Fiber Backbone, Unshielded Twisted Pair to-the-Desk
Configuring a network with unshielded twisted pa ir cabling to-the-desk is
similar to an all-fiber network becau se the cabling is star-wired in both
cases.
Be aware of the following additiona l rules for configuring a network:
❑The four-repeater rule in Ethernet limits the number o f 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 Confi guration” 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 bac k plane
For each pair of 10BASE-T Modules t hat 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 throug h another port on the
same 10BASE-T Module) that counts a s 585 meters of fiber equivalent
distance, and as a full repeater.
Example: Sample Configuration Distance Calculation
Use the following example to de termine if the 10BASE-T Transceivers i n
Figure are within legal Ethernet limits. Identi fy the two transceivers that
are likely to be the greatest fiber equivalent apart in F igure 2-8. In this
case, they are 10BASE-T Transceivers A and B.