Cabletron Systems 100BASE-FX, Cabling Manual

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Token Ring Network Requirements
10-4 IEEE 802.5 Shielded Twisted Pair
Special Cases of Link Length
If cable types are mixed in an installation, the different cable attenuations and
qualities must be compensated for. In any installation, Type 6 and Type 9 cable
may only be run for 2/3 the distance of Type 1 or Type 2 cable. This means that in
order to be equivalent to a 10 meter length of Type 1 cable, Type 6 cable must be
2/3 of 10 meters, or 6.6 meters.
When calculating the longest link length in the installation, this compensation can
be used to determine the absolute maximum Type 6 jumper cable length that may
be used. For example: If a 16 Mbps Token Ring using passive circuitry had a Type
1 STP link measuring 60 meters, the maximum length of Type 6 cable that could
be connected to it would be 26.4 m.
Figure 10-1. Type 6 Cable Calculations
Trunk Cable Length
Just as there are maximum lengths for lobe cabling, Ring-In/Ring-Out, or trunk
cables, must be within specified limits. The length limitations given here assume
that the trunk cabling under examination meets all other specifications of the
IEEE 802.5 standard for STP cabling.
IBM Type 1
The maximum link length of a Type 1 STP trunk cable at 4 Mbps is 770 m
(2,525 ft). A 16 Mbps Token Ring network would allow a maximum Type 1 STP
trunk link length of 346 m (1,134 ft). Other types of STP cable are not
recommended for use as trunk cables by the IEEE 802.5 specification.
100 m (Maximum Type 1 Cable Length)
60 m (Length of Existing Type 1 Cable)
40 m (Remaining Type 1 Length Budget)
40m
0.66
26.4 m Maximum Type 6 Cable Length
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