Cabletron Systems 100BASE-FX, Руководство по кабельной продукции

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Cabling Types 4-7
Ethernet Media
The association of pairs of wire within the UTP cable jacket are decided by the
specifications to which the cable is built. There are two main specifications in use
around the world for the production of UTP cabling: EIA/TIA 568A and the
EIA/TIA 568B. The two wiring standards are different from one another in the
way that the wires are associated with one another at the connectors.
The arrangement of the wires in the two EIA/TIA specifications does not affect
the usability of either type of connector style for 10BASE-T purposes. As the
arrangement of the wires into pairs and the twisting of the pairs throughout the
cable remain the same regardless of the EIA/TIA specification being used, the
two specifications can be considered equivalent. As the specifications terminate
the wires into different arrangements, care must be taken to keep all the cables at
a facility terminated to the same EIA/TIA standard. Failure to do so can result in
the mis-association of wires at the connectors, making the cabling unable to
provide a connection between Ethernet devices. The arrangement of the wires
and pairs in the two EIA/TIA specifications is discussed in the UTP Cable
portion of the Connector Types section of this chapter.
Keep in mind that the selection of an EIA/TIA wiring scheme determines the
characteristics of Wallplates, Patch Panels, and other UTP interconnect hardware
you add to the network. Most manufacturers supply hardware built to both of
these specifications. The more common of the two specifications in 10BASE-T
applications is EIA/TIA 568A.
Four-Pair Cable
The typical single UTP cable is a polyvinyl chloride (PVC) or plenum-rated plastic
jacket containing four pairs of wire. The majority of facility cabling in current and
new installations is four-pair cable of this sort. The dedicated single connections
made using four-pair cable are easier to troubleshoot and replace than the
alternative, bulk multipair cable such as 25-pair cable.
The jacket of each wire in a four-pair cable will have an overall color: brown, blue,
orange, green, or white. In a four-pair UTP cable (the typical UTP used in
networking installations) there is one wire each of brown, blue, green, and
orange, and four wires whose overall color is white. The white wires are
distinguished from one another by periodically placed (usually within 1/2 inch of
one another) rings of the other four colors.
Wires with a unique base color are identified by that base color: blue, brown,
green, or orange. Those wires that are primarily white are identified as
white/<color>, where <color> indicates the color of the rings of the other four
colors in the white insulator.
The 10BASE-T and 100BASE-TX standards are concerned with the use of two
pairs, Pair 2 and Pair 3 (of either EIA/TIA 568 specification). The 10BASE-T and
100BASE-TX standards configure devices to transmit over Pair 3 of the EIA/TIA
568A specification (Pair 2 of EIA/TIA 568B), and to receive from Pair 2 of the
EIA/TIA 568A specification (Pair 3 of EIA/TIA 568B). The use of the wires of a
UTP cable is shown in Table 4-1.