Insertion Loss (Attenuation); Impedance; Jitter; Crosstalk - Cabletron Systems 100BASE-FX Cabling Manual

Full-Duplex Fast Ethernet Network Requirements

Insertion Loss (Attenuation)

The maximum allowable insertion loss for any 100BASE-TX station on the Fast
Ethernet network is 11.5 dB at frequencies from 5 to 10 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.
The insertion loss characteristics of a cable are one of the main determinants of
link length allowed by the Fast Ethernet and 100BASE-TX specifications. As long
as a UTP cable does not exceed the total link length of 11.5 dB, it may be any
length up to 100 m (328 ft). The 100 meter maximum total length is based on the
total allowable propagation delay in the network, and cannot be exceeded.
NOTE

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 .
Typical UTP cables used in Fast Ethernet environments have an impedance
between 85 and 111 .

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.

Crosstalk

Crosstalk is electrical interference between wires. Crosstalk occurs when a cable
strand absorbs signals from other wires that it is adjacent to. Excessive crosstalk
can be caused by a break in the insulation or shielding that separates wires from
one another in a bundle.
Fast Ethernet UTP cables should be checked for Near-End Crosstalk, or NEXT, at
installation. The allowable amount of NEXT for a UTP cable is dependent upon
the type of cable used in the installation.
8-2
As longer cables are more susceptible to other limiting factors,
Cabletron Systems does not recommend the installation of
100BASE-TX cabling over 100 m in length.
100BASE-TX