Phan Vĩnh Thuần Computer Network 1
Chương 3:
MÔI TRƯỜNG TRUYỀN DẪN
CHO NETWORKING
Overview
•
Copper cable is used in almost every
LAN. Many different types of copper
cable are available, with each type having
advantages and disadvantages. Proper
selection of cabling is key to efficient
network operation.
Phan Vĩnh Thuần Computer Network 2
•
Optical fiber is the most frequently used
medium for the longer, high bandwidth, point-
to-point transmissions required on LAN
backbones and on WANs. Using optical media,
light is used to transmit data through thin
glass or plastic fiber. Electrical signals cause
a fiber-optic transmitter to generate the light
signals sent down the fiber. The receiving host
receives the light signals and converts them to
electrical signals at the far end of the fiber.
However, there is no electricity in the fiber-
optic cable itself. In fact, the glass used in
fiber-optic cable is a very good electrical
insulator.
Phan Vĩnh Thuần Computer Network 3
•
Physical connectivity allowed an increase in

Students completing this module
should be able to:
–
Describe the specifications and
performances of different types of
cable.
–
Describe coaxial cable and its
advantages and disadvantages over
other types of cable.
–
Describe shielded twisted-pair (STP)
cable and its uses.
–
Describe unshielded twisted-pair cable
(UTP) and its uses.
Phan Vĩnh Thuần Computer Network 6
–
Discuss the characteristics of straight-
through, crossover, and rollover cables
and where each is used.
–
Explain the basics of fiber-optic cable.
–
Describe how fibers can guide light for
long distances.
–
Describe multimode and single-mode
fiber.
–

to accurately receive and interpret the
signal by the time the signal reaches that
device? The distance the signal travels
through the cable directly affects
attenuation of the signal. Degradation of
the signal is directly related to the distance
the signal travels and the type of cable
used.
Phan Vĩnh Thuần Computer Network 10
•
Some examples of Ethernet
specifications which relate to cable type
include:
–
10BASE-T
–
10BASE5
–
10BASE2
•
10BASE-T refers to the speed of
transmission at 10 Mbps. The type of
transmission is baseband, or digitally
interpreted. The T stands for twisted
pair.
Phan Vĩnh Thuần Computer Network 11
•
10BASE5 refers to the speed of
transmission at 10 Mbps. The type of
transmission is baseband, or digitally

elements. One of these elements, located
in the center of the cable, is a copper
conductor. Surrounding the copper
conductor is a layer of flexible insulation.
Over this insulating material is a woven
copper braid or metallic foil that acts as
the second wire in the circuit and as a
shield for the inner conductor. This second
layer, or shield reduces the amount of
outside electro-magnetic interference.
Covering this shield is the cable jacket.
Phan Vĩnh Thuần Computer Network 17
•
For LANs, coaxial cable offers several
advantages. It can be run longer
distances than shielded twisted pair, STP,
and unshielded twisted pair, UTP, cable
without the need for repeaters. Repeaters
regenerate the signals in a network so
that they can cover greater distances.
Coaxial cable is less expensive than fiber-
optic cable, and the technology is well
known. It has been used for many years
for many types of data communication,
including cable television.
Phan Vĩnh Thuần Computer Network 18
•
Coaxial cable comes in a variety of sizes. The
largest diameter was specified for use as
Ethernet backbone cable, because it has a

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.
Phan Vĩnh Thuần Computer Network 21
3.1.3. Cáp STP (Shield Twisted-Pain)
Phan Vĩnh Thuần Computer Network 22
•
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).
Phan Vĩnh Thuần Computer Network 23
•
Shielded twisted-pair cable shares
many of the advantages and
disadvantages of unshielded twisted-