Cabletron Systems 100BASE-FX, Cabling Manual

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Fast Ethernet Network Requirements
7-6 Hybrid Installations
Figure 7-1. Fast Ethernet Network Radius
If the two longest links in the Fast Ethernet repeater domain are both made using
UTP cable, each UTP segment may be 100 m in length, for a total network radius
of 200 m. If these links were both made using multimode fiber optics, the
allowable maximum network radius would be 272 m, less than that allowed by a
repeater with a single 100BASE-FX link.
When media are mixed in a Fast Ethernet network, the allowable network radius
changes slightly. In a mixed UTP and multimode fiber optic network, the
maximum radius is 263 m. This means that the longest UTP segment in the Fast
Ethernet network may be up to 100 m, and the longest 100BASE-FX link may be
160 m. The maximum network radius for each Fast Ethernet media configuration
is provided in Table 7-1.
Repeater Classes
Repeaters in Fast Ethernet networking are divided into two categories, or
“classes” by the 100BASE-TX standard. The difference between these Class I and
Class II repeaters is the method each uses to handle received signals for
transmission. The different techniques result in different rules of configuration for
a Fast Ethernet network.
Class I repeaters receive the 100BASE-TX electrical signal on one interface and
translate that signal from its electrical form into a digital series, much in the same
way that a Fast Ethernet station receives a transmission. The Class I repeater then
generates a new signal on each of its interfaces using the translated digital series.
The Class I repeater does not make any decisions based of the received signal, nor
does it perform any error-checking. The translation of the received signal is
intended to improve the strength and validity of the repeated Fast Ethernet frame.
The Class II repeater receives and immediately repeats each received transmission
without performing any translation. The repeating process is a simple electrical
duplication and strengthening of the signal.
Fast Ethernet Repeater
Link A
Link B
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