Cabletron Systems 100BASE-FX, Руководство по кабельной продукции

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Cabling Types 4-9
Ethernet Media
As with four-pair cable, the wires within a 25-pair cable are identified by color.
The jacket of each wire in a 25-pair cable has an overall color: violet, green, brown,
blue, red, orange, yellow, gray, black, and white. In a 25-pair UTP cable all wires
in the cable are identified by two colors. The first color is the base color of the
insulator, while the second is the color of narrow bands painted onto the base
color. These identifying rings are periodically placed on the wire, and repeat at
regular intervals. When a wire is identified in a 25-pair cable, it is identified first
by its base color, and then further specified by the color of the bands or rings.
As a 25-pair cable can be used to make up to 12 connections between Ethernet
stations (two wires in the 25-pair cable are typically not used), the wire pairs need
to be identified not only as transmit or receive pairs, but what other pair they are
associated with. There are two ways of identifying sets of pairs in a 25-pair cable.
The first is based on the connection of a 25-pair cable to a specific type of
connector designed especially for it, the RJ21 connector. The second is based on
connection to a punchdown block, a cable management device typically used to
make the transition from a single 25-pair cable to a series of four-pair cables
easier.
For further information on the RJ21 connector, refer to the Connector Types
section later in this chapter. A description of punchdown blocks may be found in
Chapter 13, Cabling Devices, and details of the punchdowns may be found in the
Connector Types
section later in this chapter.
Table 4-2. 25-Pair Cable Pair Mapping
Port Number Wire Use Wire Color
RJ21 Pin
Number
Punchdown
In Number
Punchdown
Out Number
1
RX + White/Blue 26 A1 B1
RX - Blue/White 1 A2 B2
TX + White/Orange 27 A3 B3
TX - Orange/White 2 A4 B4
2
RX + White/Green 28 A5 B5
RX - Green/White 3 A6 B6
TX + White/Brown 29 A7 B7
TX - Brown/White 4 A8 B8
3
RX + White/Gray 30 A9 B9
RX - Gray/White 5 A10 B10
TX + Red/Blue 31 A11 B11
TX - Blue/Red 6 A12 B12