Cabletron Systems 100BASE-FX, Cabling Manual

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Ethernet Media
4-6 Cabling Types
Both the original and the inverted signal are then transmitted, the original signal
over the TX+ wire, the inverted signal over the TX - wire. As these wires are the
same length and of the same construction, the signal travels (propagates) at the
same rate through the cable. Since the pairs are twisted together, any outside
electrical interference that affects one member of the pair will have the same effect
on the other member of that pair.
The transmissions travel through the cable, eventually reaching a destination
transceiver. At this location, both signals are read in. The original signal is
unchanged, but the signal that had previously been inverted is reverted to the
original state. When this is done, it returns the encoded transmission to its
original state, but reverses the polarity of any signal interference that the encoded
transmission may have suffered.
Once the inverted transmission has been returned to the normal encoded state,
the transceiver adds the two signals together. As the encoded transmissions are
now identical, there is no change to the data content. Line noise spikes, however,
are combined with noise spikes of their exact opposite polarity, causing them to
cancel one another out.
Figure 4-5. UTP Signal Equalization
The UTP cable used in network installations is the same type of cable used in the
installation of telephone lines within buildings. UTP cabling is differentiated by
the quality category of the cable itself, which is an indicator of the type and
quality of wire used and the number of times the wires are twisted around each
other per foot. The categories range from Category 1 to Category 5, with Category
5 cabling being of the highest quality.
The wires that make up a length of UTP cable are numbered and color coded.
These color codes allow the installer of the networking cable to determine which
wires are connected to the pins of the RJ45 ports or patch panels. The numbering
of the wires in EIA/TIA standard cables is based on the color of the insulating
jacket that surrounds the core of each wire.
Inverted
Transmission
Normal
Transmission
Induced
Noise Spike
Noise spikes
cancel out
Resulting Signal
Reversion of Inverted
Transmission
Original Signal
1845n05