Cabletron Systems 100BASE-FX, Руководство по кабельной продукции

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Cabling Types 4-5
Ethernet Media
Building Network Coax (BNC) connectors crimp onto a properly prepared cable
end with a crimping tool. To prevent signal reflection on the cable, 50 Ohm
terminators are used on unconnected cable ends.
As with thick coaxial cable, thin coaxial cable allows multiple devices to connect
to a single cable. Up to 30 transceivers may be connected to a single length of thin
coaxial cable, spaced a minimum of 0.5 meter from one another. This minimum
spacing requirement keeps the signals from one transceiver from interfering with
the operation of others. The annular rings on the thin coaxial cable are placed 0.5
meter apart, and are a useful guide to transceiver placement.
Unshielded Twisted Pair (UTP)
Unshielded Twisted Pair cabling (referred to here as UTP, but also may be termed
copper wire, 10BASE-T wire, Category 3, 4, or 5 Ethernet wire, telephone cable, or
twisted pair without shielded or unshielded qualifier) is commonly made up of
two, four, or 25 pairs of 22, 24, or 26 AWG unshielded copper solid or stranded
wires. These pairs of wires are twisted together throughout the length of the
cable, and are broken up into transmit and receive pairs. In each pair, one wire
carries the normal Ethernet transmission, while its associated wire carries a copy
of the transmission that has been inverted.
Figure 4-4. UTP Cable Pair Association
The twisting of associated pairs helps to reduce the interference of the other
strands of wire throughout the cable. This is due to the method of transmission
used with twisted pair transmissions.
In any transceiver or Network Interface Card (NIC), the network protocol signals
to be transmitted are in the form of changes of electrical state. The means by
which the ones and zeroes of network communications are turned into these
signals is called encoding. In a twisted pair environment, once a transceiver has
been given an encoded signal to transmit, it will copy the signal and invert the
polarity of that signal (see Figure 4-5). The result of this inverted signal is a mirror
opposite of the original signal.
Tx+
Tx-
Rx-
Rx+
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