MÔI TRƯỜNG TRUYỀN dẫn CHO NETWORKING (MẠNG máy TÍNH cơ bản SLIDE)

Chương 3:
MƠI 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
Computer Network
1
network operation.


• Optical fiber is the most frequently used
medium for the longer, high bandwidth, pointto-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 fiberoptic cable itself. In fact, the glass used in
fiber-optic cable is a very good electrical
insulator.
Computer Network
2


• Physical connectivity allowed an increase in

productivity by allowing the sharing of
printers, servers, and software. Traditional
networked
systems
require
that
the
workstation remains stationary permitting
moves only within the limits of the media and
office area.
• The introduction of wireless technology
removes these restraints and brings true
portability to the computing world. Currently,
wireless technology does not provide the highspeed transfers, security, or uptime reliability
of cabled networks. However, flexibility of
wireless has justified the trade off.
Computer Network

3


• Administrators often consider wireless
when installing a new network or when
upgrading an existing network. A simple
wireless network could be working just a
few minutes after the workstations are
turned on. Connectivity to the Internet is
provided through a wired connection,
router, cable or DSL modem and a
wireless access point that acts as a hub

for the wireless nodes. In a residential or
small office environment these devices
may be combined into a single unit
Computer Network

4


• Students completing
should be able to:

this

module

– 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 Computer
uses.
Network

5


– Discuss the characteristics of straightthrough, 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.
– Describe the type of connectors and
equipment used with fiber-optic cable.
Computer Network

6


3.1. Đường truyền cáp đồng
3.1.1. Các đặc tả cáp
Cables have different specifications
and expectations pertaining to
performance:

Computer Network

7


• What speeds for data transmission can
be achieved using a particular type of

cable? The speed of bit transmission
through
the
cable
is
extremely
important. The speed of transmission is
affected by the kind of conduit used.
• What kind of transmission is being
considered? Will the transmissions be
digital or will they be analog-based?
Digital or baseband transmission and
analog-based
or
broadband
transmission areComputer
theNetwork
two choices. 
8


• How far can a signal travel through a
particular type of cable before attenuation
of that signal becomes a concern? In other
words, will the signal become so degraded
that the recipient device might not be able
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.
Computer Network
9


• 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.
Computer Network

10

• 10BASE5 refers to the speed of
transmission at 10 Mbps. The type of
transmission is baseband, or digitally
interpreted. The 5 represents the
capability of the cable to allow the signal
to travel for approximately 500 meters
before attenuation could disrupt the
ability of the receiver to appropriately
interpret the signal being received.
10BASE5 is often referred to as
Thicknet.
Computer Network
11


• 10BASE2 refers to the speed of
transmission at 10 Mbps. The type of
transmission is baseband, or digitally
interpreted. The 2, in 10BASE2,
represents the capability of the cable to
allow the signal to travel for
approximately 200 meters, before
attenuation could disrupt the ability of
the receiver to appropriately interpret
the signal being received. 10BASE2 is
often referred toComputer
as Network
Thinnet

12


Computer Network

13


3.1.2. Cáp đồng trục (Coaxial cable )

Computer Network

14


Computer Network

15


• Coaxial cable consists of a hollow outer
cylindrical conductor that surrounds a
single inner wire made of two conducting
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.
Computer Network

16


• 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 fiberoptic cable, and the technology is well
known. It has been used for many years
for many types of data communication,
including cable television.
Computer Network

17

• Coaxial cable comes in a variety of sizes. The
largest diameter was specified for use as
Ethernet backbone cable, because it has a
greater transmission length and noise rejection
characteristics. This type of coaxial cable is
frequently referred to as thicknet. As its
nickname suggests, this type of cable can be
too rigid to install easily in some situations.
Generally, the more difficult the network media
is to install, the more expensive it is to install.
Coaxial cable is more expensive to install than
twisted-pair cable. Thicknet cable is almost
never used anymore, except for special
purpose installations.
Computer Network
18


• In the past, ‘thinnet’ coaxial cable with
an outside diameter of only 0.35 cm
was used in Ethernet networks. It was
especially useful for cable installations
that required the cable to make many
twists and turns. Since thinnet was
easier to install, it was also cheaper to
install. This led some people to refer to
it as cheapernet.
Computer Network

19

• The outer copper or metallic braid in coaxial
cable comprises half the electric circuit and
special care must be taken to ensure a solid
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.
Computer Network

20


3.1.3. Cáp STP (Shield Twisted-Pain)

Computer Network

21

• 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).
Computer Network

22


• Shielded twisted-pair cable shares
many of the advantages and
disadvantages of unshielded twistedpair cable (UTP). STP affords greater
protection from all types of external
interference, but is more expensive
and difficult to install than UTP.

Computer Network

23


• 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. 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.
Computer Network

24


3.1.4. Cáp UTP (Unshield Twisted-Pair)

Computer Network

25