100Base-Tx; Impedance; Jitter - Cabletron Systems 100BASE-FX Cabling Manual

Enterasys 100base-fx transceivers: user guide

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Fast Ethernet Network Requirements

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.

NOTE

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.

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 .

Typical UTP cables used in Fast Ethernet environments have an impedance

between 85 and 111 .

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.

7-2

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.

100BASE-TX

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