Transcript Lecture 01 - Hong Kong Baptist University

Lecture 03
Conducted and Wireless Media
1
Introduction
• Communications are conducted through a medium,
– For example, we talked, our voice transmitted through air
• Thus, the world of computer networks would not exist if
there were no medium by which to transfer data
• The two major categories of media include:
– Conducted media
– Wireless media
(to p4)
(to p28)
• How to subscribe them for organizations?
– Selection criteria
Application examples
(to p65)
(to p3)
2
Application examples
• Conducted
– Example 1
– Example 2
(to p71)
(to p73)
• Wireless
– Example 1
– Example 2
– Example 3
(to p74)
(to p75)
(to p77)
3
Conducted media
• Physical connection between source and
sink points
• Three common media:
– i) wire
– ii) coaxial cable
– iii) optical fiber
(to p5)
(to p10)
(to p13)
– Comparison between their transmission
(to p27)
speeds
(to p2)
4
i) wire
– usually made of copper with a pair of wire
• Or called twisted pair of wire
– the pairs of wires are almost insulated with plastic
coating and twisted together -- known as twisted
pair wires
– (see Figure 9-6) (to p6)
– Categorizations
(to
p9)
– the twisting has the effect of electrically canceling
the signals radiating form each wire ---- prevents
the signals on one pair of wires from interfering
the adjacent pair
– the effect is known as crosswalk
(to
5
p4)
FIGURE 9-6
Twisted pair wires are the most commonly used medium for communications transmission.
(to
p5)
-As to oppose different layout as shown in Figure 3.2
-Different ways of twisted pair way adopted in industries
(to
p7)
(to
(to
p8)
6
p5)
(to
7
p6)
(to
8
p6)
(to
9
p5)
ii) coaxial cable
– Cable that made of several layers of material
around a central core, which often a copper
wire
– (see Figure 9-8)
(to
p12)
– has a very wide bandwidth (400 Mhz to 600
Hhz), thus carries a very high data capacity
– one coaxial cable carries up to 10,800 voice
conversations or over 50 television channles
– Its max capacity is dependent on the
thickness of the copper wire
10
– Two main applications
to p11)
(
ii) coaxial cable (cont.)
• It has two main applications:
– 1) Baseband coaxial technology uses digital
signaling in which the cable carries only one
channel of digital data
– 2) Broadband coaxial technology transmits
analog signals and is capable of supporting
multiple channels
• Disadv: it is easy to tape and thus lack of a
high security measure
(to
11
p4)
FIGURE 9-8
Parts of a coaxial cable. (to
p10)
12
iii) optical fiber
– Is a new media for comm
– is a very thin glass fiber; which core
provides the transmission capability
– the core is surrounded by another type of
glass called cladding, which protected by a
plastic coating
– (see Figure 9-9) (to p14)
– data is placed on with a light source or a
laser. Light source stays in the core as the
cladding has a low refractive index
13
(to
p17)
FIGURE 9-9
Parts of optical fiber cable.
(to
p13)
Alternative view
(to
p15)
14
Thin vs. Thick fiber optic cable
(to
p16)
(to
15
p13)
Fiber-Optic Cable (continued)
• Fiber-optic cable is capable of supporting
millions of bits per second for 1000s of meters
• Thick cable (62.5/125 microns) causes more ray
collisions, so you have to transmit slower. This
is step index multimode fiber. Typically use LED
for light source, shorter distance transmissions
• Thin cable (8.3/125 microns) – very little
reflection, fast transmission, typically uses a
laser, longer transmission distances; known as
single mode fiber
(to
16
p15)
iii) optical fiber (cont.)
– Two primary types of fiber:
• a) single mode
(to p18)
• b) multi mode
• How more lights can be traveled together
– Layout of optical fiber worldwide
(to
(to
p19)
p20)
– Fiber optic cable is difficult to splice - requires
a reflectometer to detect such work
to p22)
– SONET concept
to p24)
– Adv
to p25)
– Disv
(
(
(
17(to p4)
(to
p17)
18
Wavelength division
• Wavelength division multiplexing
– A technique which allows many light beams of
different wavelengths can travel along a single fiber
simultaneously without interfering with one another
(to
19
p17)
FIGURE 9-10a
The world’s undersea cable network.
(to
p21)
20
FIGURE 9-10b
Continued
(to
21
p17)
SONET
• Synchronous Optical Network
– A technique facilitates easy to connect carriers that
using different brands/products of their optical
networks
– It is a standard for the ANSI (American National Standard Institute)
– Transmission rate at Gpbs
(to p23)
– Data speed for different networks
(to
22
p17)
FIGURE 9-11
Comparative data rates for the SONET and ITU-T optical fiber transmission standards.
(to
23
p22)
iii) optical fiber (cont.)
– Advantages:
•
•
•
•
•
•
1) do not radiate signal as all electrical devices do
2) fiber is of light weight
3) cost of fibers is getting cheaper
4) high bandwidth - high data capability
5) little lost of signal strength
6) excellent isolation between parallel fiber crossed-talk between fiber does not exist
• 7) very secure, difficult to tape
(to
24
p17)
Disv
• Because fiber-optic cable is susceptible to
reflection (where the light source bounces
around inside the cable) and refraction
(where the light source passes out of the
core and into the surrounding cladding),
thus Fiber-optic cable is not perfect either.
Noise is still a potential problem
(to
p26)
Concepts of refraction and reflection
(to
25
p17)
Fiber-Optic Cable (continued)
(to
26
p25)
Conducted Media
(to
27
p4)
Wireless media
• Technically speaking – in wireless transmissions,
space is the medium
• Radio, satellite transmissions, and infrared light
are all different forms of electromagnetic waves
that are used to transmit data
to p29)
• Their frequencies of transmission
to p30)
• Different types of applications
• Comparisons
to p63)
(
(
(
(to
28
p2)
Wireless Media (continued)
(to
29
p28)
Applications
– i) microwave radio
to p31)
– ii) satellite
to p35)
– iii) cellular phones
to p43)
– Iv) Infrared Transmissions
to p52)
– v) Wireless Application Protocol (WAP)
– Broadband Wireless Systems
to p56)
– Bluetooth
to p59)
– Wireless Local Area Networks
to p60)
– Free Space Optics and Ultra-Wideband
(
(
(
(
(to
p53)
(to
p61)
(
(
(
30
(to
p28)
iv) microwave radio
– Is a medium most common carriers for
long distance comm (how it looks like )
to p32)
– transmit in the range of 4-28 Ghz freq
range
– up to 6000 voice circuits are carried in a 30
Mhz wide radio channel
– travel in a straight line - ie must transmit
and receive in a direct line of sight , and to p33)
signals will not pass through solid objects
to p34)
– requirement
(
(
(
31
Terrestrial Microwave
Transmission (continued)
(to
32
p31)
Terrestrial Microwave
Transmission (continued)
(to
33
p31)
iv) microwave radio (cont.)
– requires to set up an antenna in the range of
20 to 30 miles
– Capable to carry either analog and digital
form
– Disadv
• may interfere by the weather condition (why?)
(to
34
p30)
v) satellite
– Use of microwave radio, the signal travels
from a ground station on earth to a satellite
and back to another ground station
– Satellites can be classified by how far out
into orbit each one is (LEO, MEO, GEO,
to p36)
and HEO)
– radio signal is beamed to the satellite on a
specific frequency called uplink; where
rebroadcast on a different frequency called
to p39)
downlink
(
(
35
Satellite Microwave Transmission (continued)
• LEO (Low-Earth-Orbit) – 100 to 1000 miles out
– Used for wireless e-mail, special mobile telephones, pagers,
spying, videoconferencing
• MEO (Middle-Earth-Orbit) – 1000 to 22,300 miles
– Used for GPS (global positioning systems) and government
• GEO (Geosynchronous-Earth-Orbit) – 22,300 miles
– Always over the same position on earth (and always over the
equator)
– Used for weather, television, government operations
• HEO (Highly Elliptical Earth orbit) – satellite follows an elliptical orbit
– Used by the military for spying and by scientific organizations for
photographing celestial bodies
Their positions on the orbit
(to
p37)
(to
36
p35)
Satellite Microwave
Transmission (continued)
(to
p38)
(to
37
p36)
Satellite Transmission
(continued)
(to
38
p37)
v) satellite
(cont.)
– Due to the security reason, information that
being sent is first encrypted so that tapping
and interpret its content is difficult
– there exists a delay of receiving information -- called propagation delay, is called as
distance apart of comm device
=
– example
----------------------------------------speed in which data is transmitted
(to
p40)
39
v) satellite
(cont.)
– If satellite is 22,300 mile from the ground and
speed sending data is 186,000 miles per
second, then
2 x 22,300
Propagation delay =
=
---------------18,6000
0.2398 sec
– Classifications by their configuration
(to
p41)
40
Satellite (continued)
• Satellite microwave can also be classified
by its configuration:
– Bulk carrier configuration
– Multiplexed configuration
– Single-user earth station configuration (e.g.
VSAT)
Their semantic view
(to
p42)
(to
41
p30)
Satellite Microwave
Transmission (continued)
(to
42
p41)
Cellular Telephones
• Wireless telephone service, also called mobile
telephone, cell phone, and PCS
• To support multiple users in a metropolitan area
to p44)
(market), the market is broken into cells
• Each cell has its own transmission tower and set
to p45)
of assignable channels
to p46)
• Different generations of MP
(
(
(
43
Cellular Telephones (continued)
(to
44
p43)
Cellular Telephones (continued)
(to
45
p43)
Cellular Phones
•
•
•
•
1st generation
2nd generation
2.5 generation
3rd generation
(to
p47)
(to
p48)
(to
p49)
(to
p50)
(to
46
p30)
Cellular Telephones (continued)
• 1st Generation
– AMPS (Advanced Mobile Phone Service) –
first popular cell phone service; used analog
signals and dynamically assigned channels
– D-AMPS (Digital AMPS) – applied digital
multiplexing techniques on top of AMPS
analog channels
(to
47
p46)
Cellular Telephones (continued)
• 2nd Generation
– PCS (Personal Communication Systems) –
essentially all-digital cell phone service
– PCS phones came in three technologies:
• TDMA – Time Division Multiple Access
• CDMA – Code Division Multiple Access
• GSM – Global System for Mobile Communications
(to
48
p46)
Cellular Telephones (continued)
• 2.5 Generation
– AT&T Wireless, Cingular Wireless, and TMobile now using GPRS (General Packet
Radio Service) in their GSM networks (can
transmit data at 30 kbps to 40 kbps)
– Verizon Wireless, Alltel, U.S.Cellular, and
Sprint PCS are using CDMA2000 1xRTT (one
carrier radio- transmission technology) (50
kbps to 75 kbps)
– Nextel uses IDEN technology
(to
49
p46)
Cellular Telephones (continued)
• 3rd Generation
– UMTS (Universal Mobile Telecommunications
System) – also called Wideband CDMA
• The 3G version of GPRS
• UMTS not backward compatible with GSM (thus
requires phones with multiple decoders)
– 1XEV (1 x Enhanced Version) –3G
replacement for 1xRTT
• Will come in two forms:
– 1xEV-DO for data only
– 1xEV-DV for data and voice
(to
50
p46)
51
Infrared Transmissions
• Transmissions that use a focused ray of
light in the infrared frequency range
• Very common with remote control devices,
but can also be used for device-to-device
transfers, such as PDA to computer
(to
52
p30)
Wireless Application Protocol (WAP)
• WAP is a set of protocols that allows wireless
devices such as cell phones, PDAs, and twoway radios to access the Internet
• WAP is designed to work with small screens and
with limited interactive controls
• WAP incorporates Wireless Markup Language to p54)
(WML) which is used to specify the format and
presentation of text on the screen
(
• Their applications
(to
p55)
53
Wireless Application Protocol
(WAP) (continued)
(to
54
p53)
Wireless Application Protocol (WAP)
(continued)
• WAP may be used for applications such as:
– Travel directions
– Sports scores
– E-mail
– Online address books
– Traffic alerts
– Banking and news
• Possible short-comings include low speeds,
security, and very small user interface
(to
55
p30)
Broadband Wireless Systems
• Delivers Internet services into homes and
businesses
• Designed to bypass the local loop
telephone line, in a metropolitan area to p57)
• Transmits voice, data, and video over high
frequency radio signals
to p58)
• Past and future trends
(
(
56
Broadband Wireless Systems
(continued)
(to
57
p56)
Broadband Wireless Systems
(continued)
• Multichannel multipoint distribution service
(MMDS) and local multipoint distribution
service (LMDS) looked promising a few
years ago but died off
• Now companies are eyeing Wi-Max, an
IEEE 802.16 standard; initially 300 kbps to
2 Mbps over a range of as much as 30
miles; forthcoming standard (802.16e) will
allow for moving devices
(to
58
p30)
Bluetooth
• Bluetooth is a specification for short-range, point-to-point
or point-to-multipoint voice and data transfer
• Bluetooth can transmit through solid, non-metal objects
• Its typical link range is from 10 cm to 10 m, but can be
extended to 100 m by increasing the power
• Bluetooth will enable users to connect to a wide range of
computing and telecommunication devices without the
need of connecting cables
• Typical uses include phones, pagers, modems, LAN
access devices, headsets, notebooks, desktop
computers, and PDAs
(to
59
p30)
Wireless Local Area Networks
(IEEE 802.11)
• This technology transmits data between
workstations and local area networks
using high-speed radio frequencies
• Current technologies allow up to 54 Mbps
(theoretical) data transfer at distances up
to hundreds of feet
• Three popular standards: IEEE 802.11b, a,
g
• More on this in Chapter Seven (LANs)
to p30)
(
60
Free Space Optics and UltraWideband
• Free space optics
–
–
–
–
–
–
–
–
–
Uses lasers, or more economically, infrared transmitting devices
Line of sight between buildings
Typically short distances, such as across the street
Newer auto-tracking systems keep lasers aligned when buildings
shake from wind and traffic
Current speeds go from T-3 (45 Mbps) to OC-48 (2.5 Gbps) with
faster systems in development
Major weakness is transmission thru fog
A typical FSO has a link margin of about 20 dB
Under perfect conditions, air reduces a system’s power by
approximately 1 dB/km
Scintillation is also a problem (especially in hot weather)
(to
p62)
61
Free Space Optics and
Ultra-Wideband (continued)
• Ultra-wideband
– UWB not limited to a fixed bandwidth but broadcasts over a wide
range of frequencies simultaneously
– Many of these frequencies are used by other sources, but UWB
uses such low power that it “should not” interfere with these
other sources
– Can achieve speeds up to 100 Mbps but for small distances
such as wireless LANs
– Proponents for UWB say it gets something for nothing, since it
shares frequencies with other sources. Opponents disagree
– Cell phone industry against UWB because CDMA most
susceptible to interference of UWB
– GPS may also be affected
– One solution may be to have two types of systems – one for
indoors (stronger) and one for outdoors (1/10 the power)
(to
62
p30)
Wireless Media (continued)
more
(to
p64)
63
Wireless Media (continued)
(to
64
p28)
Media Selection Criteria
1.
2.
3.
4.
5.
to p66)
Cost
to p67)
Speed
Distance and expandability
to p69)
Environment
Security
to p70)
(
(
(to
p68)
(
(
(to
65
p2)
Cost
• Different types of costs
– Initial cost – what does a particular type of
medium cost to purchase? To install?
– Maintenance / support cost
• ROI (return on investment) – if one
medium is cheaper to purchase and install
but is not cost effective, where are the
savings?
(to
66
p65)
Speed
• Two different forms of speed:
– Propagation speed – the time to send the first
bit across the medium
• This speed depends upon the medium
• Airwaves and fiber are speed of light
• Copper wire is two thirds the speed of light
– Data transfer speed – the time to transmit the
rest of the bits in the message
• This speed is measured in bits per second
(to
67
p65)
Expandability and Distance
• Certain media lend themselves more
easily to expansion
• Don’t forget right-of-way issue
(to
68
p65)
Environment
• Many types of environments are
hazardous to certain media
(to
69
p65)
Security
• If data must be secure during transmission,
it is important that the medium not be easy
to tap
(to
70
p65)
Conducted Media in Action:
Example 1
• First example – simple local area network
– Hub typically used
– To select proper medium, consider:
• Cable distance
• Data rate
– Layout
(to
p72)
71
Conducted Media in Action:
Example 1
(to
72
p3)
Conducted Media in Action:
Example 2
• Second example – company wishes to
transmit data between buildings that are
one mile apart
– Is property between buildings owned by
company?
• If not consider using wireless
• When making decision, need to consider:
–
–
–
–
–
Cost
Speed
Expandability and distance
Environment
Security
(to
73
p3)
Wireless Media In Action:
Example 1
• First example – you wish to connect two
computers in your home to Internet, and
want both computers to share a printer
– Can purchase wireless network interface
cards
– May consider using Bluetooth devices
(to
74
p3)
Example 2
• Second example – company wants to
transmit data between two locations, such
as Beijing and Shanghai
– Company considering two-way data
communications service offered through
VSAT satellite system
– Layout
to p76)
(
(to
75
p3)
Wireless Media In Action:
Three Examples (continued)
(to
76
p3)
Wireless Media In Action:
Example 3
• Third example – second company wishes
to transmit data between offices two miles
apart
– Considering terrestrial microwave system
– Layout
to p78)
(
77
Wireless Media In Action:
Three Examples (continued)
(to
78
p3)