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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 (height of the wave)
Frequency


Number of times a signal’s amplitude changes over a
period of time
Expressed in hertz (Hz) (Heinrich Hertz)
Wavelength


Distances between corresponding points on a wave’s
cycle
Inverse to frequency
Freq 1,000,000 cycles/second (1MHz) – WL 300m
Freq 2,000,000 cycles/second (2MHz) – WL 150m
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 digit) can only have a value of
either 1 or 0
Eight bits together form a byte

Byte “01111001” = “121” on digital network
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
Transmission Basics
Digital more reliable than analog
Digital is less effected by noise
However, digital requires many pulses to
transmit the same info an analog signal
can transmit with a single wave
Higher reliability/efficiency make the extra
digital signaling worth it
Data Modulation
Modem


Name reflects function as modulator/demodulator
Digital to analog – analog to digital
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

Used by modern Ethernet networks

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

Commonly used to increase the amount of data
that can be transmitted in a time period
Transmission Direction
Time division multiplexing (TDM)

Divides channel into multiple intervals of time (time
slots)
Figure 4-7: Time division multiplexing
Transmission Direction
Statistical multiplexing


Similar to TDM
Assigns slots to nodes according to priority and need
instead of in succession
Figure 4-8: Statistical multiplexing
Transmission Direction
Wavelength division multiplexing (WDM)




New technology
Used only with fiber-optic cable
Data is transmitted as pulses of light
Fiber-optic modem (FOM) is a mux/demux used on fiber
networks that employ WDM
Figure 4-9: Wavelength division multiplexing
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
Figure 4-10: 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
Bandwidth measures difference between
highest and lowest frequencies a media can
transmit

Range of frequencies is directly related to
throughput
Throughput
Table 4-1: Throughput measures
Baseband and Broadband
Baseband



Transmission form in which (typically) digital
signals are sent through direct current (DC)
pulses applied to the wire
DC requires exclusive use of wire’s capacity
Example: Ethernet networks
Broadband

Transmission form in which signals are
modulated as radiofrequency (RF) analog
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
Figure 4-11: An analog signal distorted by noise
Transmission Flaws
Figure 4-12: A digital signal distorted by noise
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
Figure 4-13: An analog signal distorted by noise, and then amplified
Transmission Flaws
Regeneration

Process of retransmitting a digital signal
Repeater

Device used to regenerate a digital signal (physical layer)
Figure 4-14: A digital signal distorted by noise, and then repeated
Media Characteristics
Determining transmission media for your
network:
Throughput

Perhaps most significant factor in choosing a
transmission medium is throughput
Cost





Cost of installation – yourself vs. contractors
Cost of new infrastructure versus reusing existing
infrastructure
Cost of maintenance and support
Cost of a lower transmission rate affecting productivity
– wait times
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
Installation location very important

Conduits can protect cabling from noise

Coaxial Cable
Consists of
central
copper core
surrounded
by an
insulator,
braiding,
and outer
cover called
a sheath
Figure 4-15: Coaxial cable
Coaxial Cable
Table 4-2: 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
10Base5
Designation explanation:



10 – throughput (10 Mbps)
Base – Baseband transmission
5 – maximum segment length (500 meters)
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
In Thicknet
networking,
the
transceiver is
a separate
device and
may also be
called a
media
access unit
(MAU)
Figure 4-16: Thicknet cable transceiver with detail of a vampire tap
Thicknet Characteristics
Attachment Unit Interface (AUI)


Ethernet standard establishing physical specifications for
connecting coaxial cables with transceivers and networked
nodes
An AUI connector may also be called a DIX or DB-15
connector
Figure 4-17: AUI connectors
Thicknet Characteristics
N-series connector (or n connector)

Screw-and-barrel arrangement securely connects coaxial
cable segments and devices
Figure 4-18: 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
BNC barrel connectors are used to join two Thinnet
cable segments together