View
1
Download
0
Category
Preview:
Citation preview
� �
� �
4 - Transmission Media
Faculty of Information Technology
BUS3150 - Computer Facilities Network Management
4 - Transmission Media
Faculty of Information Technology
Monash University
� �
� �
4 - Transmission Media
2 Faculty of Information Technology
This Lecture
• Different transmission media.
– Guided transmission media:
· Twisted Pair· Coaxial Cable· Optical Fibre
– Wireless transmission:
· Terrestrial Microwave· Satellite Microwave· Broadcast Radio· Infrared
� �
� �
4 - Transmission Media
3 Faculty of Information Technology
Overview
• Guided - wire /optical fibre
• Unguided - wireless
• Characteristics and quality of a data transmission determined by mediumand signal.
– For guided, the medium is more important.
– For unguided, the bandwidth produced by the antenna is more impor-tant.
� �
� �
4 - Transmission Media
4 Faculty of Information Technology
Overview
• Key concerns are data rate and distance.
• These depend on:
– Bandwidth:
· Higher bandwidth gives higher data rate.
– Transmission impairments:
· Attenuation limits distance.· Interference and noise causes bit errors.
– Number of receivers in guided media.
· More receivers (multi-point) introduce more attenuation.
• Also need to consider cost (materials, labour and operating), security, op-erating environment, safety, reliability, maintenance and expansibility.
� �
� �
4 - Transmission Media
5 Faculty of Information Technology
Electromagnetic Spectrum for Telecommunications
102Frequency
(Hertz) 103 104 105 106 107 108 109 1010 1011 1012 1013 1014 1015
Power and telephoneRotating generatorsMusical instrumentsVoice microphones
MicrowaveRadarMicrowave antennasMagnetrons
InfraredLasersGuided missilesRangefinders
RadioRadios and televisionsElectronic tubesIntegrated circuitsCellular Telephony
ELF VF
ELF = Extremely low frequencyVF = Voice frequencyVLF = Very low frequencyLF = Low frequency
MF = Medium frequencyHF = High frequencyVHF = Very high frequency
UHF = Ultrahigh frequencySHF = Superhigh frequencyEHF = Extremely high frequency
VLF LF MF HF VHF UHF SHF EHF
Twisted Pair
Coaxial Cable
Visiblelight
OpticalFiber
FM Radioand TV
AM Radio Terrestrialand SatelliteTransmission
Wavelengthin space(meters)
106 105 104 103 102 101 100 10−1 10−2 10−3 10−4 10−5 10−6
� �
� �
4 - Transmission Media
6 Faculty of Information Technology
Guided Transmission Media
• It is possible to store data on magnetic (tapes or disks) or optical (CD orDVD) media, package the media and send using a courier.
• For extremely large sets of data, this is the cheapest method of transmis-sion. What is the down side?Andrew S. Tanenbaum, “Never underestimate the bandwidth of a station
wagon full of tapes hurtling down the highway”.
• For guided transmission, we typically consider:
– Twisted pair
– Coaxial cable
– Optical fibre
� �
� �
4 - Transmission Media
7 Faculty of Information Technology
Copper Twisted Pair
Outer insulatoror PVC
Solid copperconductors
Twist length
• Twisted pair cable consists of two insulated copper wires twisted together.
• Twisting allows each wire to have approximately the same noise level andreduces crosstalk.
• Typically installed in buildings during construction.
• Twisted pair comes in two varieties: STP and UTP.
� �
� �
4 - Transmission Media
8 Faculty of Information Technology
Effect of Noise on Parallel and Twisted-Pair Lines
Total effect is16 − 12 = 4
ReceiverSender
Noise effect = 12 units
Noise source
Noise effect = 16 units
16
12
Noise source
14
14Receiver
4
3
4 4 4
3 3 3
Sender
Total effect is14 − 14 = 0
� �
� �
4 - Transmission Media
9 Faculty of Information Technology
Twisted Pair - Applications, Pros and Cons
• Applications:
– Most common medium for both analog and digital.
– Telephone network - Between house and local exchange (subscriberloop).
– Within buildings - To private branch exchange (PBX).
– For local area networks (LAN) - 10Mbps to 1Gbps.
• Pros - Cheap and easy to work with.
• Cons - Low bandwidth/data rate and short range.
� �
� �
4 - Transmission Media
10 Faculty of Information Technology
Twisted Pair - Transmission Characteristics
• Analog:
– Needs amplifiers every 5km to 6km.
• Digital:
– Can use either analog or digital signals.
– Needs a repeater every 2 to 3km (depends on data rate).
• Limited distance.
• Limited bandwidth (1MHz).
• Limited data rate (100MHz).
• Susceptible to interference and noise.
� �
� �
4 - Transmission Media
11 Faculty of Information Technology
Unshielded and Shielded TP
• Unshielded Twisted Pair (UTP):
– Ordinary telephone wire.
– Cheapest.
– Easiest to install.
– Suffers from external EM interfer-ence.
• Shielded Twisted Pair (STP):
– Insulated twisted pairs encased in ametal braid or sheathing that reducesinterference.
– More expensive.
– Harder to handle and work with(thick, heavy).
Twisted pairs5 pairs
Plastic cover
Plastic cover Insulation CopperMetal shield
� �
� �
4 - Transmission Media
12 Faculty of Information Technology
UTP Categories
• Cat 3:
– Up to 16 MHz and 16 Mbps.
– Voice grade found in abundance in most offices.
– Twist length of 7.5 cm to 10 cm.
• Cat 4:
– Up to 20 MHz.
• Cat 5:
– Up to 100 MHz and 100 Mbps.
– Data-grade commonly pre-installed in new office buildings.
– Tighter twist (more expensive): twist length 0.6 cm to 0.85 cm.
• Cat 5E (enhanced), Cat 6, Cat 7.
� �
� �
4 - Transmission Media
13 Faculty of Information Technology
Near End Crosstalk
• Coupling of signal from one pair to another.
• Coupling takes place when transmit signal entering the link couples backto receiving pair.
• i.e. near transmitted signal is picked up by near receiving pair.
� �
� �
4 - Transmission Media
14 Faculty of Information Technology
Twisted Pair - Category Characteristics
Attenuation (dB per 100 m) Near−end Crosstalk (dB)
Frequency(MHz)
Category 3UTP
Category 5UTP 150−ohm STP
Category 3UTP
Category 5UTP 150−ohm STP
1 2.6 2.0 1.1 41 62 58
4 5.6 4.1 2.2 32 53 58
16 13.1 8.2 4.4 23 44 50.4
25 − 10.4 6.2 − 41 47.5
100 − 22.0 12.3 − 32 38.5
300 − − 21.4 − − 31.3
Category 3Class C
Category 5Class D
Category 5E Category 6Class E
Category 7Class F
Bandwidth 16 MHz 100 MHz 100 MHz 200 MHz 600 MHz
Cable Type UTP UTP/FTP UTP/FTP UTP/FTP SSTP
Link Cost(Cat 5 =1)
0.7 1 1.2 1.5 2.2
UTP = Unshielded twisted pairFTP = Foil twisted pairSSTP = Shielded screen twisted pair
� �
� �
4 - Transmission Media
15 Faculty of Information Technology
Coaxial Cable
Outer conductor(shield)
Plastic cover Inner conductor
Insulator
• A coax cable consists of the following:
– A centre conductor - usually copper.
– A metallic outer conductor (shield), serves as aground.
– An insulator covering the centre conductor.
– A plastic jacket.
� �
� �
4 - Transmission Media
16 Faculty of Information Technology
Coaxial Cable - Applications
• Most versatile transmission medium.
• Television distribution:
– Ariel to TV.
– Cable TV (hundreds of TV channels up to a few tens of km).
• Long distance telephone transmission:
– Can carry 10,000 voice calls simultaneously (FDM).
– Mostly replaced by fibre optic, microwave and satellite.
• Short distance computer systems links.
• Local area networks.
� �
� �
4 - Transmission Media
17 Faculty of Information Technology
Coaxial Cable - Transmission Characteristics
• Superior frequency characteristics to twisted pair.
• Performance limited by attenuation and noise.
• Analog signals:
– Amplifiers every few km, closer if higher frequency.
– Up to 500 MHz
• Digital signals:
– Repeater every 1km, closer for higher data rates.
� �
� �
4 - Transmission Media
18 Faculty of Information Technology
Refraction and Reflection (Snell’s law)
More dense medium(water or glass)
BeamLess dense medium (air)
I
R
(a) From less dense to more dense medium
More dense medium(water or glass)
Less dense medium (air)
I
R
Beam
(b) From more dense to less dense medium
angleCritical
Angle ofincidence reflection
Angle of
� �
� �
4 - Transmission Media
19 Faculty of Information Technology
Refraction and Reflection Examples
You cannot see the pavement
� �
� �
4 - Transmission Media
20 Faculty of Information Technology
Refractive Index
• The refractive index of a medium is a measure of the speed at which lighttravels in it.
• It is proportional to the density of the medium.
• Index of refraction, n =
Speed of light in vacuumSpeed of light in the medium.
• For example:
– Vacuum: n = 1.0 ←−Fast
– Air: n = 1.0002926
– Water: n = 1.333
– Glass: n = 1.5
– Diamond: n = 2.419 ←−Slow
� �
� �
4 - Transmission Media
21 Faculty of Information Technology
Optical Fiber
Light at less thancritical angle isabsorbed in jacket
Angle ofreflection
Angle ofincidence
Cladding
Plastic coating
Core
• Glass or plastic core surrounded by a cladding with different optical prop-erties and coated in acrylate (plastic) for protection.
• Refractive index (density) of the core is higher than the refractive index ofthe cladding. Acts as a wave guide (total internal reflection) to trap lightin the core.
� �
� �
4 - Transmission Media
22 Faculty of Information Technology
Optical Fiber - Advantages
• Mechanical characteristics of fiber:
– Small diameter, light weight.
– Flexible.
– Resistance to corrosive materials.
• Electrical characteristics of fiber:
– Low attenuation.
– Wide bandwidth.
– Electromagnetic immunity.
– Ground loop elimination.
– No electromagnetic radiation.
• Greater repeater spacing.
• Large capacity.
• Space efficiency.
• Easy installation.
• Higher security.
� �
� �
4 - Transmission Media
23 Faculty of Information Technology
Optical Fiber - Applications
• Long-haul trunks:
– Average about 1500 km with high capacity (20 - 60,000 voice chan-nels).
– Undersea optical fiber being used.
• Metropolitan trunks:
– Average about 12 km with 100,000 voice channels per trunk group.
– Join telephone exchanges.
• Rural exchange trunks:
– Ranging from 40 to 160 km with fewer than 5000 voice channels.
• Cable TV networks.
• Subscriber loops: telephone, data, video, etc.
• LANs: 100 Mbps to 1 Gbps.
� �
� �
4 - Transmission Media
24 Faculty of Information Technology
Optical Fiber - Transmission Characteristics
• Act as wave guide (total internal reflection) for 1014 to 1015 Hz.
– Portions of infrared and visible spectrum.
• Light Emitting Diode (LED):
– Cheaper.
– Wider operating temperature range.
– Last longer.
• Injection Laser Diode (ILD):
– More efficient.
– Greater data rate.
• Wavelength division multiplexing: multiple light beams at different fre-quencies (colours).
� �
� �
4 - Transmission Media
25 Faculty of Information Technology
Optical Fiber - Transmission Modes
Source Destinationindex (n)
Refractive
(a) Step-index Multimode
Source Destinationindex (n)
Refractive
(b) Graded-index Multimode
Source Destinationindex (n)
Refractive
(c) Single Mode
� �
� �
4 - Transmission Media
26 Faculty of Information Technology
Optical Fiber - Dimensions
125
50
Multi-mode Fiber
125
7
Single-mode FiberDimensions in Micrometers (µm)
• Due to the dimensions:
– Multi-mode enables the use of cheap LED light sources.
– Single-mode requires more expensive laser sources.
� �
� �
4 - Transmission Media
27 Faculty of Information Technology
Optical Fiber - Cable� �
� �
4 - Transmission Media
28 Faculty of Information Technology
Optical Fiber - Attenuation
800 900
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
1000 1100 1200 1300Wavelength (nanometer)
850nmBand
1300nmBand
1550nmBand
Atte
nuat
ion
(dB
/km
)
1400 1500 1600 1700 1800
• Depends on the light wavelength and the physical properties of the glass.
• Three low attenuation windows centred on 850, 1300 and 1550nm.
� �
� �
4 - Transmission Media
29 Faculty of Information Technology
Attenuation of Typical Guided Media
� ��� ��� ��� ��� ��� ��
� �� � � �� � �
�������������� �!"$#%�&('
)* +, -./ 012 3 * .4 )5 */ 1 2 67 89 : :; <= > +
�
� ��� ? � � � @ � � � A � � �B � �� �� � �C � �D � � � D �
�
E� �
� EGF�
FEIH�
JKL MN O PQRS T T UJS L MN O PQRV T T UJ JL MN O PQR K T T UWXL MN O PQR X T T U
QR V T TYZ[\ Y]^ _`[a
� �� � �� � �� � �b
� �� � � �� � �
��������������(�!�"$#%�& '
)5 +c 6 *d . *e f * 5 e 1 )5 */ 12 67 8g :h h <i > +
�E
� �� EI
F�FEI
H�
jklm n`o p]PX R V T T U
q � � r � � � � � � � � � � � F� � � H� � �s � � � E � � � t � � � u � �
vw x y z{| } xw �� �~ � ~ �
�������������� �!"$#%�&('
) f +� 3 0. f * e �. 5 14 ) 5 */ 1 2 67 8� 9 : : i� > +
��� E
�� ��� E
F� �F� E
H� �
� �� � � �� � �
��������������(�!�"$#%�& '
)2 +c 6� 3 6/ . 0 1 �4 * 3�
�E
� �� EI
F�FEI
H�
Y � _[ n` p� _ Y[ n` p�[ o ]a
X R V T Tn� `�
� �
� �
4 - Transmission Media
30 Faculty of Information Technology
Wireless Transmission
• Unguided media.
• Transmission and reception via antenna.
• Two basic configurations:
– Directional:
· Focused beam.· Careful alignment required.
– Omnidirectional:
· Signal spreads in all directions.· Can be received by many antennae.
– The higher the signal frequency, the more possible it is to focus.
� �
� �
4 - Transmission Media
31 Faculty of Information Technology
Frequencies
• 30 MHz to 1 GHz:
– Omnidirectional.
– Broadcast radio and television.
• 2 GHz to 40 GHz:
– Microwave.
– Highly directional.
– Point to point.
– Satellite.
• 3×1011 to 2×1014:
– Infrared.
– Point-to-point and multipoint ina confined area.
MF and HF
300 KHz 30 MHz3 MHz
CB radio
AM radio
530 1700
VHF
2 − 6Channels
7 − 13Channels
30 MHz 300MHz
TVAircraftFMTV
Paging
2161741088854
UHF
14 − 69Channels
Mobiletelephone
Cellularradio
3GHz
MicrowaveUHF TV
Paging
806470300 MHz
SHF and EHF
Microwave
3 GHz 300 GHz30 GHz
� �
� �
4 - Transmission Media
32 Faculty of Information Technology
Terrestrial Microwave
• Used for long haul telecommunications and short point-to-point links.
• Parabolic dish (typical size of 3 m diameter) creates a focused beam.
• Line of sight to receiving antenna (substantial height above ground).
• Microwave relay towers used to achieve distance.
• Higher frequencies give higher data rates and require smaller antennas.
• Attenuation is increased with rainfall (especially above 10 GHz).
Earth
Modulated signals
80 km4 − 10 GHz
100 m
� �
� �
4 - Transmission Media
33 Faculty of Information Technology
Satellite Microwave
• Satellite is a microwave relay station.
• Satellite receives on one frequency, amplifies or repeats signal and trans-mits on another frequency.
– e.g. uplink 5.925-6.425 GHz and downlink 3.7-4.2 GHz.
• Operates best in the range of 1 to 10 GHz.
• May require geo-stationary orbit:
– To maintain line of sight, requires a height of 35,784km.
– High propagation delay (0.25s).
• Typical Uses:
– Television.
– Long distance telephone.
– Private business networks.
� �
� �
4 - Transmission Media
34 Faculty of Information Technology
Satellite - Point-to-Point Link
Satelliteantenna
Earthstation
� �
� �
4 - Transmission Media
35 Faculty of Information Technology
Satellite - Broadcast Link
Satelliteantenna
Multiplereceivers
Transmitter
Multiplereceivers
� �
� �
4 - Transmission Media
36 Faculty of Information Technology
Orbit Classifications
Altitude (km)
35,000
30,000
25,000
20,000
15,000
10,000
5,000
0
GEO
MEO
Upper Van Allen belt
Lower Van Allen belt
LEO
• GEO: geo-stationary earth orbit
• MEO: medium earth orbit (e.g. 24 Global Positioning System (GPS) satellites).
• LEO: low earth orbit (e.g. Iridium (66 satellites) and Teledesic (288 satellites)).
� �
� �
4 - Transmission Media
37 Faculty of Information Technology
Example LEO: Iridium System
• Iridium system consists of 66 satellites providing global communication.
• Has an orbit height of 780 km and period of around 100 minutes.
(a) (b)
Fig. 2-18. (a) The Iridium satellites form six necklaces around theearth. (b) 1628 moving cells cover the earth.
� �
� �
4 - Transmission Media
38 Faculty of Information Technology
Broadcast Radio
• Omnidirectional: no need for rigidly mounted dish antennas.
• FM radio and UHF and VHF television.
• Line of sight.
• Less affected by rainfall and longer wavelength suffers relatively less attenuation.
• Suffers from multipath interference:
– Reflections (e.g. ghosting on TV).
� �
� �
4 - Transmission Media
39 Faculty of Information Technology
Infrared
• Modulate non-coherent infrared light.
• Line of sight (or reflection from light-coloured surface).
• Blocked by walls.
• e.g. TV remote control, IRD port.
� �
� �
4 - Transmission Media
40 Faculty of Information Technology
Further Reading
• Stallings, W., “Data and Computer Communications”, Prentice Hall. Chap-ter 4.
• Forouzan, B. A., “Data Communication and Networking”, McGraw-Hill.Chapter 7. Satellites covered in Chapter 17.
Recommended