Chapter Four
Transmission Basics and
Networking Media
Objectives
Explain data transmission concepts including fullduplexing, attenuation, and noise
Describe the physical characteristics of coaxial
cable, STP, UTP, and fiber-optic media
Explain the benefits and limitations of different
networking media
Identify the best practices for cabling buildings and
work areas
Describe the methods of transmitting data through
the atmosphere
Transmission Basics
Transmission has two meanings:


Refers to process of issuing data signals on a
medium
Refers to progress of data signals over a
medium
On a data network, information can be
transmitted via one of two methods:


Analog
Digital
Transmission Basics
Both analog and digital signals are generated
by electrical current, pressure of which is
measured in volts
In analog signals, voltage varies continuously
In digital signals, voltage turns off and on
repeatedly
Transmission Basics
Analog signal
Signals 0 and 1 are transmitted as
electric waves.
Digital signals
Code 1 is transmitted when applying
a specific voltage and code 0 is
transmitted in the case of 0V.
.
Figure 4-1: Example of an analog and digital signal
Transmission Basics
Amplitude

Measure of a signal’s strength
Frequency


Number of times a signal’s amplitude changes
over a period of time
Expressed in hertz (Hz)
Wavelength

Distances between corresponding points on a
wave’s cycle
Transmission Basics
Phase

Refers to progress of a wave over time in relationship to a
fixed point
Figure 4-2: Phase differences
Transmission Basics
Figure 4-3: A complex analog signal representing human speech
Transmission Basics
Binary system encodes using 1s and 0s
Bits = binary signal (1 or 0)
8 bits = 1 byte
Noise or any interference that may degrade
signals affects digital signals less than analog
signals
Transmission Basics
Figure 4-4: Example of a digital signal
Data Modulation
Modem

Name reflects function as modulator/demodulator
Modulation

Technique for formatting signals
Frequency modulation (FM)

Method of data modulation in which frequency of
carrier signal is modified by application of a data
signal
Amplitude modulation (AM)

Modulation technique in which amplitude of carrier
signal is modified by application of a data signal
Data Modulation
Figure 4-5: A carrier wave modified by frequency modulation
Transmission Direction
Simplex

Signals travel in only ONE direction
Half-duplex

Signals may travel in BOTH directions over a
medium BUT in only one direction at a time
Full-duplex


Signals are free to travel in BOTH directions
over a medium simultaneously
Also referred to just as duplex
Transmission Direction
Channel

Distinct communication path between two or more nodes
Figure 4-6: Simplex, half-duplex, and full-duplex transmission
Simplex, half-duplex, and full-duplex communication
Transmission Direction
Multiplexing



Allows multiple signals to travel simultaneously
over one medium
To accommodate multiple signals, single medium
is logically separated into subchannels
For each type of multiplexing:
Multiplexer (mux) is required at sending end of
channel
Demultiplexer (demux) separates the combined
signals and regenerates them in original form
Multiplexer & Demultiplexer
Transmission Direction
Time division multiplexing (TDM)

Divides channel into multiple intervals of time
Figure 4-7: Time division multiplexing
Transmission Direction
Wavelength division multiplexing (WDM)



Used only with fiber-optic cable
Data is transmitted as pulses of light
Fiber-optic modem (FOM) is a demultiplexer used on fiber
networks that employ WDM
Figure 4-9: Wavelength division multiplexing
Relationships Between Nodes
Point-to-point

Transmission involving 1 transmitter and
1 receiver
Broadcast

Transmission involving 1 transmitter and
multiple receivers
Point-to-point TRANSMISSION
Broadcast TRANSMISSION
Relationships Between Nodes
Figure 4-10: Point-to-point versus broadcast transmission
Point-to-point versus broadcast
transmission
Throughput and Bandwidth
Throughput is amount of data the medium
can transmit during a given period of time

Also called capacity .Unit = bit/s
Bandwidth measures difference between
highest and lowest frequencies a media can
transmit .Unit = Hz/Mhz.

Range of frequencies is directly related to
throughput
Transmission Flaws
NOISE
a) Electromagnetic interference (EMI)
 Interference that may be caused by motors, power
lines, television, copiers, fluorescent lights, or other
sources of electrical activity
b) Radiofrequency interference (RFI)
 Interference that may be generated by motors, power
lines, televisions, copiers, fluorescent lights, or
broadcast signals from radio or TV towers
c) Crosstalk
signal traveling on a wire or cable infringes on
signal traveling over adjacent wire or cable
Transmission Flaws
Noise
random background
mixed up with your
signal
Ex: switch on radio +
‘hiss sound’
Unit = dB
Figure 4-11: An analog signal distorted by noise
Transmission Flaws
Figure 4-12: A digital signal distorted by noise
Transmission Flaws
Attenuation - for analogue signal


Loss of signal strength as transmission travels away from source
Analogue signals pass through an amplifier, which increases not only
voltage of a signal but also noise accumulated
To strengthen analogue signals :An analog signal distorted by noise, and then amplified
Transmission Flaws
Attenuation - for digital signal
Regeneration

Process of retransmitting a digital signal
Repeater

Device used to regenerate a signal
A digital signal distorted by noise, and then repeated
Question???
What is the different between noise and
attenuation???
Latency
Delay between transmission and receipt of
a signal
Causes:
a) Media delays may be caused by the finite speed that
signals can travel through the physical
media(propagation delay)
b) Circuits delay may be caused by the electronics that
process along the path.
c) Software delays maybe caused by the decisions that
software must make to implement switching & protocols.
TRANSMISSION MEDIA
Coaxial Cable
Consists of
central
copper core
surrounded
by an
insulator,
braiding,
and outer
cover called
a sheath
(protective
covering)
Coaxial cable
Coaxial Cable
Some types of coaxial cable
Thicknet (10Base5)
Also called thickwire Ethernet
Rigid coaxial cable used on original
Ethernet networks
IEEE designates Thicknet as
10Base5 Ethernet
Almost never used on new networks
but you may find it on older networks
 Used to connect one data closet
to another as part of network backbone
Thicknet Characteristics
Throughput

According to IEEE 802.3, Thicknet transmits
data at maximum rate of 10 Mbps
Cost

Less expensive than fiber-optic but more
expensive than some other types of coaxial
cable
Connector

Can include a few different types of
connectors, which are very different from
those used on modern networks
Thicknet Characteristics
N-series connector (or n connector)

Screw-and-barrel arrangement securely connects coaxial
cable segments and devices
N-Series connector
Thicknet Characteristics
Noise immunity

Because of its wide diameter and excellent
shielding, has the highest resistance to noise
of any commonly used types of network wiring
Size and scalability

Because of its high noise resistance, it allows
data to travel longer than other types of
cabling
Thinnet (10Base2)
Also known as thin Ethernet
Characteristics:

Throughput
Can transmit at maximum rate of 10 Mbps

Cost
Less expensive than Thicknet and fiber-optic cable
More expensive than twisted-pair wiring

Connectors
Connects wire to network devices with BNC T-connectors
A seen in Figure 4-19, BNC barrel connectors are used
to join two Thinnet cable segments together
Thinnet (10Base2)
Characteristics
(cont.):

Size and scalability
Allows a maximum
of 185 m per
network segment
(see Figure 4-20)

Noise immunity
More resistant than
twisted-pair wiring
Less resistant than
twisted-pair wiring
Thinnet BNC connectors
Thinnet (10Base2)
Signal bounce



Caused by
improper
termination on
a bus network
Travels
endlessly
between two
ends of
network
Prevents new
signals from
getting through
A 10Base2 Ethernet network
Twisted-Pair (TP) Cable
Color-coded pairs of
insulated copper wires
twisted around each
other and encased in
plastic coating
Twists in wire help
reduce effects of
crosstalk

Number of twists per
meter or foot known as
twist ratio
Alien Crosstalk

When signals from
adjacent cables interfere
with another cable’s
transmission
Twisted-pair cable
Shielded Twisted-Pair (STP)
STP cable consists of twisted wire pairs that are
individually insulated and surrounded by shielding
made of metallic substance
STP cable
Unshielded Twisted-Pair
Consists of one or more insulated wire pairs
encased in a plastic sheath
Does not contain additional shielding
UTP cable
Unshielded Twisted-Pair
To manage
network cabling, it
is necessary to be
familiar with
standards used on
modern networks,
particularly
Category 3 (CAT3)
and Category 5
(CAT5)
A CAT5 UTP cable
• Use for voice communication
• Most often use for phone line
• Used for Data Transmission
• Individual pairs are wrapped in a
shield & then entire 4 pairs
wrapped in another shield.
• Supports 1000 Mbps – 10Gbps
• Used for Data Transmission
• An added separator is between
each pair of wires allowing it to
function at higher speed.
• Supports 1000 Mbps – 10Gbps
• Used for Data Transmission
• Cat 5 support 100Mbps
• Cat 5e support 1000Mbps
Comparing STP and UTP
Throughput

Both can transmit up to 100 Mbps
Cost

Typically, STP is more expensive
Connector

Both use RJ-45 connectors (see Figure 4-27) and data
jacks
Noise immunity

STP is more noise-resistant
Size and scalability

Maximum segment length for both is 100 meters
RJ-45 Connector
An RJ-45 connector
Fiber-Optic Cable
Contains one or
several glass
fibers at its
core

Surrounding
the fibers is a
layer of glass
called
A fiber-optic cable
cladding
Front view
Fiber-Optic Cable
Single-mode
fiber

Carries light
pulses along
single path
Single-mode fiber-optic cables
Fiber-Optic Cable
Multimode fiber
Many pulses of light generated
by LED travel at different
angles
Multi-mode fiber-optic cables
Fiber-Optic Cable
Throughput
 Reliable in transmitting up to 1 gigabit per second
Cost
 Most expensive type of cable
Noise immunity
 Unaffected by either EMI or RFI
Size and scalability
 Network segments made from fiber can span 100
meters
 Signals transmitted over fiber can experience
optical loss
Fiber-Optic Cable
Two popular connectors used with fiber-optic
cable:


ST connectors
SC connectors
ST and SC fiber connectors
Atmospheric Transmission Media
Infrared transmission



Infrared networks use infrared light
signals to transmit data through space
Direct infrared transmission depends
on transmitter and receiver remaining
within line of sight
In indirect infrared transmission,
signals can bounce off of walls, ceilings,
and any other objects in their path
Atmospheric Transmission Media
RF transmission

Radio frequency (RF) transmission relies

on signals broadcast over specific frequencies
Two most common RF technologies:
Narrowband
Spread spectrum
Choosing the Right Transmission
Media
Areas of high EMI or RFI
Corners and small spaces
Distance
Security
Existing infrastructure
Growth
Chapter Summary
Information can be transmitted via analog or digital
methodology
Throughput is the amount of data a medium can
transmit during a given period of time
Noise is interference that distorts an analog or digital
signal
Costs depend on many factors
There are three specifications that dictate size and
scalability of networking media
Connectors connect wire to the network device
Chapter Summary
Coaxial cable consists of central copper core
surrounded by an insulator and a sheath
Thicknet cabling is a rigid coaxial cable used
for original Ethernet networks
Both Thicknet and Thinnet coaxial cable rely
on bus topology and must be terminated at
both ends with a resistor
Twisted-pair cable consists of color-coded
pairs of insulated copper wires, twisted
around each other and encased in plastic
coating
Chapter Summary
STP cable consists of twisted pair wires
individually insulated and surrounded by a
shielding made of metallic substance
UTP cabling consists of one or more
insulated wire pairs encased in a plastic
sheath
Fiber-optic cable contains one or several
glass fibers in its core
On today’s networks, fiber is used primarily
as backbone cable