Cabletron Systems 100BASE-FX, Cabling Manual

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Fast Ethernet Network Requirements
7-2 100BASE-TX
The TIA/EIA 568A cabling specification for Category 5 compliant UTP
installations allows the use of two different types of cable: horizontal wire and
patch wire. The specification allows horizontal wire to be used to cover distances
of up to 90 m, while patch wire is restricted to a maximum length of 10 m.
Horizontal wire must be constructed with solid core wires. Horizontal wire is
intended to be used as the “in-the-wall” cabling of the network. Patch wire is
constructed with more flexible stranded core wires, and is useful in situations
where bending or movement of the wire is expected. Patch wire should only be
used for connections between punchdown blocks, patch panels, or workstations.
Insertion Loss (Attenuation)
The maximum allowable insertion loss for any 100BASE-TX station on the Fast
Ethernet network is 24.0 dB at a frequency of 100 MHz. This calculation must take
all cabling devices in the cable path into account. A typical insertion loss test must
include the jumper cabling used at the station and at the wiring closet, and any
patch panels, punchdown blocks, and wallplates in the installation.
Impedance
Cabletron Systems 100BASE-TX equipment requires that 100BASE-TX cables in
the Fast Ethernet network have an impedance within the range of 75 to 165
Ω
.
Typical UTP cables used in Fast Ethernet environments have an impedance
between 85 and 111
Ω
.
Jitter
Jitter may be caused by intersymbol interference and reflection of signal.
Networking technologies that rely on particular timing or clocking schemes may
be affected by jitter due to excessive signal reflection. Any 100BASE-TX cable
installation should not exceed 1.4 ns of jitter. If a cable run meets the 100BASE-TX
impedance requirements (detailed above), jitter should not be a concern.
NOTE
A third type of TIA/EIA 568 A cabling, backbone wire, does not
apply to this implementation of the 100BASE-TX standard, and
is not discussed in this chapter.