Cabletron Systems 100BASE-FX, Cabling Manual

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Cabling Terms
2-6 Test Characteristics
Port
A port is a set of pins or channels on a networking or cabling device that are
arranged to accept a connector. Ports are constructed much like connectors, and
will only accept the connector type they are specifically designed for. Ports may
be keyed, gendered, or locking, in the same fashion as connectors.
Jack
A jack is a term that is usually synonymous with port, and indicates a port
location. Typically, the term refers to ports located on wallplates or other passive
cabling devices.
Test Characteristics
The following section deals with the various important specifications and testing
information related to the cabling and connectors used in LAN environments.
Impedance
Impedance is the resistance that a conductive cable offers to the transmission of
current. Impedance is measured in ohms (
Ω
). Cables with high Impedance values
are highly resistant to the transmission of electrical signals. Some network
operation specifications and network devices require the use of cabling with
specific impedance levels and will not work properly with cabling having
significantly higher or lower values.
Crosstalk
Crosstalk is electrical interference between wires in a multi-stranded cable, such
as Unshielded Twisted Pair (UTP) cabling. Crosstalk occurs when a cable strand
or group of strands absorb signals from other wires that they are adjacent to.
Crosstalk can be caused by a break in the insulation or shielding that separates
wires from one another in a bundle.
Noise
In regards to network cabling, the term noise refers to electrical noise, electrical
signals that are spontaneously introduced onto a cable due to that cables
proximity to noise sources. Typical sources of electrical noise include lighting
fixtures, electric motors, and transformers.