SYSTEM ADMINISTRATION
Chapter 4
Network Media, Connectors,
and Their Characteristics
Understanding Ethernet
Standards
• The IEEE 802 standard addresses hardware that
interacts with the Physical and Data Link layers of
the OSI Model.
• The two most common media are twisted pair wire
and coaxial cable.
Twisted Pair Cable
• Twisted pair wire, the same type used to connect
telephones, is used to connect network devices together.
UTP contains four wire pairs (eight wires total).
• Each type includes at least two pairs of insulated copper
wires that are twisted together and housed in a plastic
sheath.
• Higher categories have more twists per foot, which
provides for better throughput and less chance of
crosstalk or outside electromagnetic interference (EMI).
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Twisted Pair Cable
(continued)
• For 10Base-T networks, the twisted pair cabling must be
rated at a minimum of Category 3, although Categories 4
and 5 may also be used.
• Twisted pair wire used in data networks can be either
unshielded (UTP) or shielded (STP).
• The sheath or exterior covering of the cable pairs can be
either plenum grade or non-plenum grade.
• Twisted pair cabling uses RJ-45 connectors.
10Base-T
• Shielded or unshielded twisted pair cable is used.
• RJ-45 connectors are used to terminate one or more
ends of the cable. The cable may also be terminated at
a punch-down block or in the back of a patch panel.
• Each station has its own network cable and it is not
shared with any other stations.
• Network speeds are 10 Mbps.
• A maximum of 1024 stations are allowed per network.
• The maximum distance of a cable run is 100 meters (328
feet).
100Base-T
• 100Base-T Ethernet works just like regular Ethernet
except that it can obtain data transfer speeds up to
100 Mbps.
• Fast Ethernet can be divided into two categories:
– 100Base-TX
– 100Base-T4
• Both 100Base-TX and 100Base-T4 work with
twisted pair cable.
100Base-T4
• 100Base-T4 can attain data transfer speeds up to
100 Mbps over Category 3 cable.
• 100Base-T4 uses four pairs of wiring (all eight
wires).
100Base-TX
• 100BaseTX requires Category 5, unshielded twisted
pair cable.
• All associated networking hardware, such as patch
panels and connectors, must comply with Category
5 standards.
10Base-2 - Thin Coaxial Cable
• Coaxial cable has two conductors, a center copper
core that is shrouded by insulating Teflon or plastic
foam, and a foil wrap or a braided metal shield that
covers the insulating plastic foam. The inner core
carries the electrical signals while the outer foil wrap
shields against noise.
• Coaxial cable is commonly used in a bus
configuration.
• 10Base-2 networks use RG-58 cable (Thinnet).
Cable types RG 58 A/U or RG 58 C/U are commonly
used.
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10Base-2 - Thin Coaxial Cable
(continued)
• Each end of the segment must be equipped with a
50-ohm terminating resistor.
• Pieces of coaxial cable may be no shorter than 0.5
meter (1.64 feet) in length. This means that the
minimum spacing between network connections
must be at least 0.5 meter.
• Thinnet segments may be a maximum of 185
meters (607 feet) long.
10Base-5 - Thick Coaxial Cable
• Thick coaxial cable, also known as Thicknet (RG-8/RG11), is commonly used in 10Base-5 networks.
• Thicknet is well suited for network backbones or for
connecting hubs.
• Uses RG-8 or RG-11 cable, which has a solid center
conductor.
• Uses a thick (0.4-inch diameter) and inflexible coaxial
cable. The outer casing of the cable may be polyvinyl
chloride (PVC), which will be yellow in color, or Teflon,
which will be an orange or brown color.
• Plenum cable may be required to meet fire regulations.
(continued)
10Base-5 - Thick Coaxial Cable
(continued)
• Must be terminated at each end with 50-ohm terminators
and should be grounded at one end for electrical safety
reasons.
• A maximum of 100 devices may be attached to a
segment.
• Pieces of Thicknet may be no shorter 2.5 meters. This
means that the minimum spacing between network
connections must be at least 2.5 meters.
• Each segment has a maximum length of 500 meters,
which may be extended with repeaters. A maximum of
five segments may be used.
• Transceivers are used to attach nodes to the cable.
Fiber-Optic Cabling
• Instead of using copper wire to transmit electrical
signals, fiber-optic cabling uses light-conducting
glass fibers as its core.
• Data is then transmitted either through pulses of
light that are sent by a laser or light-emitting diodes
(LED).
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Fiber-Optic Cabling
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• There are several different types of fiber-optic cabling:
– Single-mode: Contains a single, tiny strand of fiber-optic
glass, usually 7.1 or 8.5mm in diameter. Single-mode fiber
is typically used in telephone applications, cable television,
or as a backbone.
– Multimode: In multimode fiber, the core is usually 62.5 mm
in diameter, much larger than that used by single-mode.
Multimode can handle many rays at once, making it ideal
for voice and data applications. Multimode cable is the
most commonly used in computer networks.
– Simplex fiber: Simplex is a cable containing a single
strand of fiber.
– Duplex fiber: Duplex is a cable with two strands of fiber
bound together in separate jackets.
(continued)
Fiber-Optic Cabling
(continued)
• Must follow the prescribed bend radius when installing
(i.e., if the cable is bent too sharply, it will break).
• Difficult to terminate and there are several types of
connectors in use. Must ensure you purchase the
correct connectors, especially when working in an area
where fiber has already been installed.
• Fiber-optic cable is expensive. When buying in bulk,
expect to pay about $1.00 per foot.
• Fiber-optic devices, such as network cards and media
converters, must also be used.
(continued)
Fiber-Optic Cabling
(continued)
• Very secure since data is transmitted using
pulses of light rather than electrical signals.
• Resistant to EMI since it does not transmit
electrical signals.
• Maximum length is measured in miles,
approximately 2.4 (or 4 kilometers).
• Does not attenuate very quickly.
• The most common connectors used for fiber-optic
cabling are either ST or SC connectors.
100Base-FX
• 100Base-FX uses fiber-optic cabling to transfer data
at 100 Mbps, while maintaining Ethernet standards.
• Advantages:
– It provides a fast, reliable, and secure connection.
– It is highly resistant to EMI.
– Can transmit up to approximately 4 kilometers
(approximately 2.4 miles).
• Disadvantages
– Very expensive, especially when compared to
100Base-T using copper wiring.
– It is more difficult than copper to install and terminate.
– Must also purchase networking hardware with fiber
connections or purchase media converters.
Gigabit Ethernet
• Gigabit Ethernet is a transmission technology that is
based on Ethernet standards.
• Provides a data transfer rate of 1 billion bits per
second (one gigabit).
• Frequently used as the backbone in large-enterprise
networks.
• Fiber-optic cable is the primary medium used on
Gigabit Ethernet networks, although copper cable
may be used for very short distances.
Troubleshooting Network
Cabling Problems
• Although each cable type has some unique features,
there are some features that they all have in common.
The steps listed below can be used with all cable types:
– Ensure the connectors are secure. Pull lightly on each
connector to ensure it is firmly attached.
– Check to make sure the connector is installed correctly.
– Check the cable for severe kinks or damage. Replace
damaged cables.
– Measure the cable to ensure it does not exceed maximum
distance limitations.
– Make use of cable testers if the wire is suspect.
– When using copper cable, ensure they do not cross
fluorescent lights or other sources of electromagnetic
interference.
Twisted Pair Cable
• Look at the wire colors in the connector. Are the wire
pairs inserted correctly? Check both ends.
• Ensure you are not using a crossover cable instead
of a straight-through cable, and vice versa,
depending on the intended purpose of that wire.
• Check the length of all cables involved in the run.
For example, the maximum length of twisted pair
cable is 100 meters. This means that if the patch
cable (running from the computer to the wall jack) is
10 meters long, the cable run (from the back of the
wall jack to the hub or switch) cannot exceed 90
meters.
Coaxial Cable
• Termination is one of the most common problems in a
network using coaxial cable. When more than one
computer has trouble communicating, always check that
the connector is attached. If you suspect a bad
connector, try another one.
• Ensure you are using the right type of wire. Do not use
cable intended for television installations on a computer
network.
• When working with Thicknet, ensure the vampire taps
are secure.
• Remember the 5-4-3 rule:
– 5 total segments
– 4 repeaters
– 3 segments with devices
Fiber-Optic Cable
• Observe the bend radius. The glass fibers may
break when bent too severely.
• Fiber-optic cable should be laid in a metal raceway
or conduit for protection.
• Check the connectors. Adding connectors to fiberoptic cable is tedious, exacting work and requires
practice.