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Chapter Four
Transmission Basics and
Networking Media
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
Figure 4-1: Example of an analog 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 can only have a value of either 1 or 0
Eight bits together form a 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
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
Transmission Direction
Time division multiplexing (TDM)

Divides channel into multiple intervals of time
Transmission Direction
Statistical multiplexing


Similar to TDM
Assigns slots to nodes according to priority and need
instead of in succession
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
Relationships Between Nodes
Point-to-point

Transmission involving one transmitter and
one receiver
Broadcast

Transmission involving one transmitter and
multiple receivers
Webcasting

Broadcast transmission used over the Web
Relationships Between Nodes
Throughput and Bandwidth
Throughput is amount of data the medium
can transmit during a given period of time

Also called capacity
Bandwidth measures difference between
highest and lowest frequencies a media can
transmit

Range of frequencies is directly related to
throughput
Throughput
Baseband and Broadband
Baseband

Transmission form in which (typically) digital
signals are sent through direct current (DC)
pulses applied to the wire
Broadband

Transmission form in which signals are
modulated as radiofrequency (RF) pulses that
use different frequency ranges
Transmission Flaws
Electromagnetic interference (EMI)

Interference that may be caused by motors,
power lines, television, copiers, fluorescent lights,
or other sources of electrical activity
Radiofrequency interference (RFI)

Interference that may be generated by motors,
power lines, televisions, copiers, fluorescent
lights, or broadcast signals from radio or TV
towers
Transmission Flaws
Transmission Flaws
Transmission Flaws
Attenuation


Loss of signal strength as transmission travels away from source
Analog signals pass through an amplifier, which increases not
only voltage of a signal but also noise accumulated
Transmission Flaws
Regeneration

Process of retransmitting a digital signal
Repeater

Device used to regenerate a signal
Media Characteristics
Throughput

Perhaps most significant factor in choosing a
transmission medium is throughput
Cost





Cost of installation
Cost of new infrastructure versus reusing existing
infrastructure
Cost of maintenance and support
Cost of a lower transmission rate affecting productivity
Cost of obsolescence
Media Characteristics
Size and scalability

Specifications determining size and
scalability:
Maximum nodes per segment
Maximum segment length
Maximum network length

Latency is the delay between the
transmission of a signal and its receipt
Media Characteristics
Connectors

Connects wire to network device
Noise immunity



Thicker cables are generally less susceptible
to noise
Possible to use antinoise algorithms to protect
data from being corrupted by noise
Conduits can protect cabling from noise
Coaxial Cable
Consists of
central
copper core
surrounded
by an
insulator,
braiding,
and outer
cover called
a sheath
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
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 (10Base2)
Signal bounce



Caused by
improper
termination on
a bus network
Travels
endlessly
between two
ends of
network
Prevents new
signals from
getting through
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
Shielded Twisted-Pair (STP)
STP cable consists of twisted wire pairs that are
individually insulated and surrounded by shielding
made of metallic substance
Unshielded Twisted-Pair
Consists of one or more insulated wire pairs
encased in a plastic sheath
Does not contain additional shielding
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)
10BaseT
Popular Ethernet networking standard that replaced
10Base2 and 10Base5 technologies
10BaseT
Enterprise-wide
network


Spans entire
organization
Often services
needs of many
diverse users
100BaseT
Enables LANs to run at 100-Mbps data
transfer rate
Also known as Fast Ethernet
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
Fiber-Optic Cable
Contains one or
several glass
fibers at its
core

Surrounding
the fibers is a
layer of glass
called
cladding
Fiber-Optic Cable
Single-mode
fiber

Carries light
pulses along
single path
Multimode fiber

Many pulses of
light generated
by LED travel at
different angles
Fiber-Optic Cable
Throughput

Reliable in transmitting up to 1 gigabit per
second
Cost

Most expensive type of cable
Connector

You can use any of 10 different types of
connectors (see Figure 4-30)
Fiber-Optic 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
10BaseF and 100BaseFX
10BaseF

Physical layer standard for networks
specifying baseband transmission, multimode
fiber cabling, and 10-Mbps throughput
100BaseFX

Physical layer standard for networks
specifying baseband transmission, multimode
fiber cabling, and 100-Mbps throughput
Physical Layer Networking
Standards
Cable Design and Management
Cable plant

Hardware
comprising
enterprise-wide
cabling system
Structured cabling

Method for
uniform,
enterprise-wide,
multivendor
cabling systems
Cable Design and Management
Entrance facilities
Backbone wiring

Backbone cabling that provides vertical
connections between floors of a building are
called risers
Cable Design and Management
Equipment room
Telecommunications
closet

Punch-down
block is a panel of
data receptors

Patch panel is a
wall-mounted panel
of data receptors
Cable Design and Management
Horizontal wiring
Cable Design and Management
Work area

Patch cable is a
relatively short
section of twistedpair cabling with
connectors on both
ends that connect
network devices to
data outlets
Cable Design and Management
Installing Cable
Installing Cable
Installing Cable
Straight-through cable

Terminations at both ends are identical
Crossover cable

Terminations locations of transmit and receiver wires on one end
of cable are reversed
Installing Cable
Do not untwist twisted-pair cables more than
one-half inch before inserting them
Do not strip off more than one inch of
insulation from copper wire in twisted-pair
cables
Watch bend radius limitations for cable
being installed
Test each segment of cabling with cable tester
Use only cable ties to cinch groups of cable
together
Installing Cable
Avoid laying cable across floor where it
may sustain damage
Install cable at least three feet away from
fluorescent lights or other sources of EMI
Always leave slack in cable runs
If running cable in plenum, area above
ceiling tile or below subflooring, make sure
cable sheath is plenum-rated
Pay attention to grounding requirements
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