electrical connection at both ends resulting in
proper grounding. Poor shield connection is one of the biggest
sources of connection problems in the installation of coaxial
cable. Connection problems result in electrical noise that
interferes with signal transmittal on the networking media. For
this reason thinnet is no longer commonly used nor supported by
latest standards (100 Mbps and higher) for Ethernet networks.
Web Links Coaxial Cable http://searchnetworking.techtarget.com/
sDefinition/0,,sid7_ gci211806,00.html
Content 3.1
Copper Media 3.1.8 STP cable Shielded
twisted-pair cable (STP) combines the techniques of shielding,
cancellation, and twisting of wires. Each pair of wires is
wrapped in metallic foil. The four pairs of wires are wrapped
in an overall metallic braid or foil. It is usually 150-Ohm
cable. As specified for use in Ethernet network installations,
STP reduces electrical noise within the cable such as pair to
pair coupling and crosstalk. STP also reduces electronic noise
from outside the cable, for example electromagnetic
interference (EMI) and radio frequency interference (RFI).
Shielded twisted-pair cable shares many of the advantages and
disadvantages of unshielded twisted-pair cable (UTP). STP
affords greater protection from all types of external
interference, but is more expensive and difficult to install
than UTP. A new hybrid of UTP with traditional STP is Screened
UTP (ScTP), also known as Foil Twisted Pair (FTP). ScTP is
essentially UTP wrapped in a metallic foil shield, or screen.
It is usually 100-Ohm or 120-Ohm cable. The metallic shielding
materials in STP and ScTP need to be grounded at both ends. If
improperly grounded or if there are any discontinuities in the
entire length of the shielding material, STP and ScTP become
susceptible to major noise problems. They are susceptible
because they allow the shield to act like an antenna picking up
unwanted signals. However, this effect works both ways. Not
only does the shield prevent incoming electromagnetic waves
from causing noise on data wires, but it also minimizes the
outgoing radiated electromagnetic waves. These waves could
cause noise in other devices. STP and ScTP cable cannot be run
as far as other networking media, such as coaxial cable or
optical fiber, without the signal being repeated. More
insulation and shielding combine to considerably increase the
size, weight, and cost of the cable. The shielding materials
make terminations more difficult and susceptible to poor
workmanship. However, STP and ScTP still have a role,
especially in Europe. Web Links Networking Basic's
Cables and Stuff http://www.waterwheel.com/Guides/
networking_basics_ 0006.htm
Content 3.1 Copper
Media 3.1.9 UTP cable Unshielded
twisted-pair cable (UTP) is a four-pair wire medium used in a
variety of networks. Each of the 8 individual copper wires in
the UTP cable is covered by insulating material. In addition,
each pair of wires is twisted around each other. This type of
cable relies solely on the cancellation effect produced by the
twisted wire pairs, to limit signal degradation caused by EMI
and RFI. To further reduce crosstalk between the pairs in UTP
cable, the number of twists in the wire pairs varies. Like STP
cable, UTP cable must follow precise specifications as to how
many twists or braids are permitted per foot of cable.
TIA/EIA-568-A contains specifications governing cable
performance. It calls for running two cables, one for voice and
one for data, to each outlet. Of the two cables, the one for
voice must be four-pair UTP. CAT 5 is the one most frequently
recommended and implemented in installations today. Unshielded
twisted-pair cable has many advantages. It is easy to install
and is less expensive than other types of networking media. In
fact, UTP costs less per meter than any other type of LAN
cabling. However, the real advantage is the size. Since it has
such a small external diameter, UTP does not fill up wiring
ducts as rapidly as other types of cable. This can be an
extremely important factor to consider, particularly when
installing a network in an older building. In addition, when
UTP cable is installed using an RJ-45 connector, potential
sources of network noise are greatly reduced and a good solid
connection is practically guaranteed. There are disadvantages
in using twisted-pair cabling. UTP cable is more prone to
electrical noise and interference than other types of
networking media, and the distance between signal boosts is
shorter for UTP than it is for coaxial and fiber optic cables.
UTP was once considered slower at transmitting data than other
types of cable. This is no longer true. In fact, today, UTP is
considered the fastest copper-based media. When communication
occurs, the signal that is transmitted by the source needs to
be understood by the destination. This is true from both a
software and physical perspective. The transmitted signal needs
to be properly received by the circuit connection designed to
receive signals. The transmit pin of the source needs to
ultimately connect to the receiving pin of the destination. The
following are the types of cable connections used between
internetwork devices. In Figure , a LAN switch is connected to
a computer. The cable that connects from the switch port to the
computer NIC port is called a straight-through cable. In Figure
, two switches are connected together. The cable that connects
from one switch port to another switch port is called a
crossover cable. In Figure , the cable that connects the RJ-45
adapter on the com port of the computer to the console port of
the router or switch is called a rollover cable. The cables are
defined by the type of connections, or pinouts, from one end to
the other end of the cable. See images two, four, and six. A
technician can compare both ends of the same cable by placing
them next to each other, provided the cable has not yet been
placed in a wall. The technician observes the colors of the two
RJ-45 connections by placing both ends with the clip placed
into the hand and the top of both ends of the cable pointing
away from the technician. A straight through cable should have
both ends with identical color patterns. While comparing the
ends of a cross-over cable, the color of pins #1 and #2 will
appear on the other end at pins #3 and #6, and vice-versa. This
occurs because the transmit and receive pins are in different
locations. On a rollover cable, the color combination from left
to right on one end should be exactly opposite to the color
combination on the other end. Lab Activity Lab Exercise:
Communications CircuitsIn this lab, the student will design,
build, and test a simple communication system. Lab
Activity Lab Exercise: Fluke 620 Basic Cable TestingIn this
lab, the student will use a simple cable tester to verify
whether a straight-through or crossover cable is good or bad.
Lab Activity Lab Exercise: Straight-Through Cable
ConstructionIn this lab, the student will build a Category 5 or
Category 5e (CAT 5 or 5e) unshielded twisted pair (UTP)
Ethernet network patch cable or patch cord and test the cable
for continuity and correct pinouts, the correct color of wire
on the right pin. Lab Activity Lab Exercise: Rollover
Cable ConstructionIn this lab, the student will build a
Category 5 or Category 5e (CAT 5 or 5e) unshielded twisted pair
(UTP) console rollover cable and test the cable for continuity
and correct pin-outs, the correct wire on the right pin. Lab