Transcript Network Media - Las Positas College

Network Media
Chapter 4
Signal Transmission
Network Media
Signal Transmission
Signaling—the way data is transmitted
across the media
 Digital signaling
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Two discrete states
• 0 or 1, on or off

Analog signaling

Constantly changing electromagnetic waves
Digital Signaling

Two different voltages are used. One
voltage to represent on and another
voltage to represent off
Data
0 0 1 1 0 1 0 0
Voltage
Time
0 1 2 3 4 5 6 7
Analog Signaling
Constantly changing electromagnetic
wave
 Characteristics:
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Amplitude
• Strength of signal (height of wave)
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Frequency
• Amount of time needed to complete one cycle
of the wave
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Phase
• Relative state of one wave in reference to
another wave
Attenuation/Noise
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Loss of signal strength as signal travels across
media
Signal must be amplified or regenerated to
ensure that data is transmitted correctly
Noise on media can disrupt data signal
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Static, cross-talk, etc.
Electromagnetic interference (EMI)
Radio frequency interference (RFI)
Amplifiers and regenerators are used to
increase the distance that signals can travel
Converting Analog to Digital

Modems
At sending computer, convert computer
digital signal to analog signal for transmission
via media
 At receiving computer, convert analog signal
to digital signal
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Modulator/Demodulator
Transmission Direction
Simplex—transmission of data in one
direction only (television)
 Half-duplex—transmission of data in both
directions but only one direction at a time
(CB radio)
 Full-duplex—simultaneous sending and
receiving of data (telephone)
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Multiplexers
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Enables multiple signals to travel
simultaneously by combining two or more
separate signals and transmitting them
together.
Multiplexer (mux) at sending end combines
signals and demultiplexer (demux) at receiving
end separates signals

Example: Cable TV--numerous signals travel through
coaxial cable; circuitry in the TV, VCR, or cable box
separate the signals into different channels
Multiplexing Methods
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Time Division Multiplexing
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Statistical Multiplexing
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Divides channel into time slots--each
device is allotted a time slot
Number of time slots allotted for each
device varies depending on priority and
need
Wavelength Division Multiplexing

Used for fiber-optic (light); different
wavelength used for each channel
Throughput/Bandwidth

Throughput is the amount of data that can be
sent across the network media in a given
time.
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Bandwidth is the range of frequencies that
the media can transmit
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Measured in bits per second
Frequently throughput and bandwidth are used
interchangable
Two methods for allocating bandwidth:
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Baseband
Broadband
Baseband
Transmission signals use the entire media
bandwidth.
 Commonly used for digital signaling.
 Most LANs use baseband signaling

Broadband
Media bandwidth is divided into multiple
channels.
 Each channel can carry different analog
signals
 Broadband networks support multiple
simultaneous signals over a single
transmission medium

Network Adapters (NICs or NACs)
Provide the physical connection between
your computer and the network media
 Transmit and receive data

Prepare data for the network cable
 Send the data to another computer or device
 Control the flow of data between the
computer and the network media

Media Characteristics
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Throughput/bandwidth
Cost
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Scalability
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Node Capacity—max # of node,
Attenuation—max length of segment, max number of
segments
Noise immunity
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Installation—cable cost, ease of installation
Maintenance—troubleshooting, repairing, replacing
electromagnetic interference, radio frequency
interference, and eavesdropping
Connectors
Network Media
Anything that carries the message through the
network

Copper
• Coaxial cable
• Twisted-pair cable
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Glass
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Wireless (Air)
• Radio waves
• Microwaves
• Infrared
• Fiber-optic cable
 Transmission media—Physical path through
which computers send and receive signals
Coaxial Cable (Coax)

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Copper core surrounded by insulation and a
sheath
Shielding makes it more resistant to
interference
Two types of coax cable used in networks
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Thinnet (10Base2)—RG 58 A/U
Thicknet (10Base5)—RG 62
Thinnet
Thicknet
Coaxial cable showing various layers
Outer shield
Insulation (PVC, Teflon)
Copper wire mesh or
aluminum sleeve
Conducting core
Thicknet cable transceiver with detail of
a vampire tap piercing the core
Thicknet
Vampire tap
Transceiver
Drop Cable
Coaxial Cable
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Terminators used at both ends of network to
prevent signal bounce back
Used with bus topology
BNC cable connector used for Thinnet cable; nconnectors are used for Thicknet
BNC T-connector
BNC cable connector
BNC Terminator
Coaxial Characteristics
T h in n e t (1 0 B a se 2)
T h ick n et (1 0 B a se 5 )
C o st
R e la tive ly in e xp e n sive M o re th a n C a teg ory 5
In sta lla tio n
R e la tive ly e a sy
M o re d ifficu lt
B a n d w id th
10 M bps
10 M bps
Nodes
30
100
A tte n u atio n
1 8 5 m ete rs
5 0 0 m ete rs
EMI
B e tte r th a n U T P
B e tte r th a n U T P
C o n n e cto rs B N C
n co n n e cto rs
Twisted-Pair Cable

Similar to telephone wiring
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Color-coded pairs of wire; twisted and encased in
plastic coating
Unshielded twisted-pair and shielded
twisted-pair cables UTP
STP
Shielding
RJ-45 connector and jack
Twisted Pair Cable Categories
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Category 1-2: Voice communications and low speed data
communications.
Category 3: Suitable for computer networks. Data
transmission rates up to 10 Mbps. Currently used for
phone installations (home)
Category 4: Data transmission rates up to 20 Mbps
Category 5: Data transmission rates up to 100 Mbps. Very
popular for LANs.
Category 5E: Higher speeds are possible (200 Mbps);
more twists
Category 6: Speeds up to six times faster than Cat 5
Category 7: Speeds up to 1 Ghz (Gigabit)
UTP Characteristics
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Cost: Relatively inexpensive; depends on
grade of copper and any enhancements
Installation: Easy to install
Bandwidth: 10-100 Mbps (Cat 5)
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Higher speeds are possible (up to 1000Mbps—
Cat5E, Cat 6 and Cat 7)
Node Capacity: Two (computer to hub)
Attenuation: 100 meters
EMI: Very susceptible to EMI and
eavesdropping
Connector: RJ-45
STP Characteristics
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Cost: Relatively inexpensive (more UTP, less
than Thicknet or fiber-optic.
Installation: Slightly more difficult than UTP
Bandwidth: same as UTP
Node Capacity: Two
Attenuation: 100 meters
EMI: Susceptible to EMI (but less susceptible
than UTP) and eavesdropping
Connector: RJ-45
Plenum Cable
A plenum is the space between the false
ceiling and the floor above.
 Plenum-grade cable is fire resistant and
produces a minimum of smoke
 More expensive than PVC cable and less
flexible
 May be required by fire code
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Fiber-optic cable
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Contains one or more glass fibers (core)
Data transmitted via pulsing light
Two categories: Single-mode and multi-mode
Optical fiber (core)
Fiber-optic connectors:
ST and SC
Glass cladding
Protective outer sheath
(jacket)
Fiber-optic Characteristics
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Cost: More expensive than copper cable
Installation: More difficult than copper cable
Bandwidth: 100 Mbps to 1 Gbps
Node: 2
Attenuation: Several kilometers
EMI: Not subject to EMI; immune to
eavesdropping
Connectors: ST and SC are popular
Cable Media Comparison
F a c to r
UTP
STP
C o a x ia l
F ib e r-o p tic
C ost
In s ta lla tio n
B a n d w id th
Low est
Easy
1 0 -1 0 0 M b p s
(typ ic a l)
2
M o d e ra te
F a irly e a s y
1 0 -1 0 0 M b p s
(typ ic a l)
2
M o d e ra te
F a irly e a s y
T yp ic a lly 1 0 M b p s
H ig h e s t
D iffic u lt
1 G bps
(1 0 0 M b p s )
2
A tte n u a tio n
H ig h (1 0 0
m e te rs )
H ig h (1 0 0
m e te rs )
EMI
Yes
C o n n e c to rs
R J -4 5
Y e s b u t le s s
th a n U T P
R J -4 5
N odes
3 0 (1 0 b a s e 2 )
1 0 0 (1 0 b a s e 5 )
Low er
T h in n e t--1 8 5 m
T h ic k n e t--5 0 0 m
Y e s b u t le s s th a n
U TP and S TP
B N C (th in n e t)
N c o n n e c to rs
(th ick n e t)
Low est
(s e ve ra l
k ilo m e te rs)
No
ST and SC
Wireless Media (Atmospheric)
Infrared
 Radio Frequency (RF)
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Narrow-band
 Spread-spectrum
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Microwaves
Wireless portable computer using an
infrared light beam to print
Infrared
Infrared Transmission Systems
Use infrared light to transmit signals
 Point-to-Point (Direct) or Broadcast
(Indirect)
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Point-to-Point (Direct)—highly focused and
directed at a specific target
• Line of Site
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Broadcast—spread the signal to cover a
wider area and allow reception of signal by
several receivers
• Signal can be bounced off walls and ceilings
Infrared Characteristics
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Line of site
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Bandwidth: 100 Kbps to 16 Mbps
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Light must be able to reach target
Tested at up to 100Mbps but slower speeds are
currently standard
Attenuation: Depends upon the quality of light
and atmospheric conditions
EMI: Can be affected by intense light. Pointto-Point transmissions are fairly immune to
eavesdropping. However, broadcast
transmission are more easily intercepted.
Wireless portable computer connecting
to a cabled network access point
Network
Radio Frequencies Characteristics
F re q u e n c y
ra n g e
C ost
In s ta lla tio n
B a n d w id th
A tte n u a tio n
EMI
N a rro w b a n d
S in g le fre q u e n c y
M o d e ra te
S im p le
U p to 1 0 M b p s
H ig h
Poor
S p re a d -s p e c tru m
M u ltip le fre q u e n c ie s
s im u lta n e o u s ly
M o d e ra te
M o d e ra te
U p to 1 0 M b p s
H ig h
F a ir
Wireless bridge connecting two LANs
Microwave Transmission
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Terrestrial Microwave
Line of site (max distance ~ 23 miles)
 Transmission can be affected by
atmospheric conditions (rain/fog).
Vulnerable to EMI, jamming and
eavesdropping
 Bandwidth 1-10 Mbps
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Satellite Microwave
Can transmit data over vast distances
 Extremely expensive if you put up your
own satellite
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Example of Network Wiring
patch cable
Example Wiring Closet