Transcript Coaxial cable Chapter 8 Transmission Media

Computer Networking
网络课件
双语教学
模拟实验
计算机网络教研室
CHAPTER 8
TRANSMISSION MEDIA
1
The first section
2
Exercises
3
Online lecture
Department of Computer
Networking Application
Chapter 8 Transmission Media
8.1 INTRODUCTION
Media
transmission
Conducted or
guided media
Radiated or
unguided media
A type of media that
provides some type of
physical path, such as
wire, cable, or optical
fiber, along which the
signal moves from end to
end .
most commonly
known today as
wireless,such as radio
waves,microwaves,or
infrared waves,through
air,water,or a vacuum.
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Chapter 8 Transmission Media
8.2 CONDUCTED MEDIA
8.2.1 Unshielded Twisted Pair Wire
Figure 8-1 Twisted pair wires are the most commonly used
medium for communications transmission.
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Chapter 8 Transmission Media
Twisting a pair of wires together has
the effect of electrically canceling the
signals radiating from each wire .
The Electrical Industries
Association(EIA) has defined six
categories of UTP for telephone and data
transmission use. P150
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Chapter 8 Transmission Media
Cat 3
Cat 5
Wire containing at
least three twists per
foot and that is about
the same as normal
telephone cable
installed in most
office buildings is
called CAT 3.
CAT 5 cable normally
contains four pairs of
wires and is the type
that is most commonly
being installed in new
homes and businesses,
particularly when it is
known that a computer
network will be used.
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Chapter 8 Transmission Media
When UTP is use in a data application it is
normally terminated with a RJ-45 jack. P151
The purpose of a terminating block or a
punchdown block is to be responsible for providing
and maintaining all wiring within the building. P152
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Chapter 8 Transmission Media
Figure 8-2
Wires installed outside may be buried or hung
from poles above ground.
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Chapter 8 Transmission Media
8.2.2 Shielded Twisted Pair Wire（STP）
Twisted pair wire is placed inside a thin
metallic shielding,similar to aluminum foil and
then enclosed in an outer plastic casing.
STP cable is infrequently used because it is
difficult to work with.
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Chapter 8 Transmission Media
8.2.3 Coaxial cable
Figure 8-3
Parts of coaxial cable.
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Chapter 8 Transmission Media
Coaxial cable is advantageous when
taps in the cable need to be made—it is
easier to tap than optical fiber.
The most common connector used in
networking applications is the British
Naval Connector(BNC).
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Chapter 8 Transmission Media
8.3 OPTICAL FIBER
The optical fiber is a very thin glass fiber of high purity.
The core of an optical fiber is surrounded by another
type of glass called the cladding.
Data are placed on an optical fiber with a light source,
either an LED or a laser.
The total diameter of an optical fiber is less than that of
a human hair.
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Chapter 8 Transmission Media
8.3 OPTICAL FIBER
光发射机原理示意图
光接收机光电转换原理示意图
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Chapter 8 Transmission Media
Figure 8-4
Parts of optical fiber cable.
Single mode optical fiber is more expensive
than multimode fiber.
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Chapter 8 Transmission Media
Structure of Optical Fiber Cable
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Chapter 8 Transmission Media
8.3 OPTICAL FIBER
The characteristic of optical fiber include:
 high bandwidth;
 difficult to tap and splice;
 not subject to electrical interference;
 cable is very small diameter and lightweight.
 little loss of signal strength;
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Chapter 8 Transmission Media
8.4 WIRELESS MEDIA
8.4.1 Microwave Radio
Microwave radio signals travel in a
straight line,and cann’t follow the
curvature of the earth so it is necessary for
the transmitting and receiving antennas to
be in a direct LOS.
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Chapter 8 Transmission Media
8.4.2 Satellite
Satellites in geosynchronous orbits circle
the earth at 22,300 miles.
The radio signal beamed from the Earth at
a satellite is called the uplink，where it is
received,amplified,and then rebroadcast on a
different frequency,called the downlink.
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Chapter 8 Transmission Media
Figure 8-5
Satellite transmission.
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Chapter 8 Transmission Media
Propagation delay is the delay that occurs because
light and radio signals only travel at 186,000 miles per
second.
A type of satellite commonly used to send television
programming into homes is called a direct broadcast
satellite.
Satellites in medium earth orbits(MEO) are
approximately 6,000 miles high.
Low earth orbit(LEO) satellites orbit at between 300
and 1000 miles high.
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Chapter 8 Transmission Media
8.4.3 Infrared
Infrared transmissions require the sender
and receiver to be in direct line of sight.
8.4.4 Free Space Optics
The use of modulated laser beams to send
data between locations that are within LOS of
each other is called Free space optics (FSO).
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Chapter 8 Transmission Media
8.6 SUMMARY OF MEDIA CHARACTERISTICS
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课后习题
Exercises
1.The radio signal beamed from the Earth at a satellite is called
the （ A ）.
√
A、 uplink
× B、 downlink
× C、 data link
× D、 control link
Redo
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Answer
Chapter 8 Transmission Media
课后习题
Exercises
2.The most popular cable for networking being installed in new
office buildings is （ D ）.
× A、 STP
× B、 optical fiber
× C、 CAT 3
√
D、 CAT 5
Redo
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Answer
Chapter 8 Transmission Media
课后习题
Exercises
3.Multiplexing on optical fibers is performed by using（ B ）.
× A、 FSK
√
B、 WDM
× C、 FDM
× D、 PAM
Redo
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Answer
Chapter 8 Transmission Media
课后习题
Exercises
4. The type of media that provides some type of physical path is
called （ D ）.
× A、 unguided media
× B、 physical media
× C、 wireless media
√
D、 conducted media
Redo
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Answer
Chapter 8 Transmission Media
课后习题
Exercises
5.Twisting a pair of wires together has the effect of（ C ）.
× A、 shielding the wire from outside interference
× B、 strengthening the pair against breakage
√
C、 electrically canceling the signals radiating from each wire
× D、 amplifying the signal flowing through the wire
Redo
Next
Answer
Chapter 8 Transmission Media
课后习题
Exercises
unguided media.
6.Air is an example of _________
Answer
7.The most appropriate media to use when there is a need for
optical fiber .
very high bandwidth and high security is _____________
Answer
guided media.
8.Twisted pair wire is an example of _________
Answer
Chapter 8 Transmission Media
课后习题
Exercises
optical fiber include: high bandwidth,
9. The characteristic of ___________
difficult to tap and splice; not subject to electrical interference,
cable is very small diameter and lightweight.
Answer
10.A type of satellite commonly used to send television
direct broadcast satellite .
programming into homes is called a _____________________
Answer
Chapter 8 Transmission Media
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