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NT1210 Introduction to Networking
Unit 4:
Chapter 4, Transmitting Bits
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Class Agenda 1/12/16
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Learning Objectives
Lesson Presentation and Discussions.
Class Quiz: Quiz 1
Lab Activities will be performed in class.
Assignments will be given in class.
Break Times. 10 Minutes break in every 1
Hour.
• Note: Submit all Assignment and labs
due today.
PHYSICAL LAYER
NETWORK CONCEPTS
Objectives
 Explain the fundamentals of electrical circuits.
 Identify different types of physical cabling.
 Identify wireless network communication needs.
 Distinguish among the different needs for wired and
wireless networks.
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Objectives
 Differentiate among major types of LAN and WAN
technologies and specifications and determine how
each is used in a data network.
 Explain basic security requirements for networks.
 Install a network (wired or wireless), applying all
necessary configurations to enable desired connectivity
and controls.
 Explain the fundamentals of electrical circuits.
 Identify different types of physical cabling.
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Transmitting Bits: Communication Analogy
 In networks, nodes send data to each other over link:
Sending node acts like person talking; receiving node
acts like person listening.
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Sending Bits with Electricity and Copper
Wires: Electrical Circuits
 Electrical circuit must exist as complete loop of
material (medium) over which electricity can flow.
 Material used to create circuit can’t be just any material;
must be good electrical conductor (e.g., copper wire).
Simple Direct Current Circuit Using a Battery
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Figure 4-2
Sending Bits with Electricity and Copper
Wires: Electrical Circuits
 Direct Current (DC) electrical circuits
 Electrical current: Amount of electricity that flows past single
point on circuit (amount of electron flow in circuit).
 Current always flows away from negative (-) lead in circuit and
towards positive (+) lead.
Powering a Light Bulb with a DC Circuit
Figure 4-3
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Sending Bits with Electricity and Copper
Wires: Frequency, Amplitude, Phase
 DC circuit (on left) and AC circuit (on right) both use 1 volt.
 DC shows constant +1 volt signal.
 AC circuit slowly rises to +1 volt, falls to 0 then falls to -1
volt (1 volt, but in opposite direction), repeating over time.
 Resulting AC wave: Sine wave
Graphs of 1 Volt (Y-Axis) over time: DC (Left) vs AC (Right)
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Figure 4-4
Sending Bits with Electricity and Copper
Wires: AC Frequency, Amplitude, Phase
 To send data, networking Physical layer standards can
change amplitude, frequency, phase, period of AC
electrical signal
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Graphs of AC Circuit: Amplitude, Period, Frequency
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Figure 4-5
Sending Bits with Electricity and Copper
Wires: AC Frequency, Amplitude, Phase
• Frequency is the rate of change with
respect to time.
• Change in a short span of time
means high frequency.
• Change over a long span of
time means low frequency.
Encoding Options: Frequency, Amplitude, and Phase Shifts
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Figure 4-6
Table 3.1 Units of period and frequency
2.12
Sending Bits with Electricity and Copper Wires:
AC Frequency, Amplitude, Phase, Period
Wave
Feature
Electrical Feature it
Represents
Definition of the Graph
Maximum height of the curve
over the centerline.
Number of complete waves
Frequency
(cycles) per second (in Hertz).
Amplitude
Phase
Period
Voltage
Speed with which current
alternates directions.
Voltage jumps, which makes
Single location in repeating wave. signal graph jump to new
phase.
Time for voltage to change
Time (width on x-axis) for one
from maximum positive
complete wave to complete.
voltage back to same point
again.
Common Features Used by Encoding Schemes
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Table 4-1
Comparison of analog and digital signals
Note
The bandwidth of a composite signal is the
difference between the
highest and the lowest frequencies
contained in that signal.
2.15
Sending Bits with Electricity and Copper
Wires: Circuit Bit Rates
 Bit rate (link speed): Defines number of bits sent over link
per second (bps).
 Impacts how nodes send data over circuit.
Example where Encoder Changes Signal Every Bit Time
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Figure 4-10
Sending Bits with Electricity and Copper
Wires: Using Multiple Circuits
 Simplex transmissions are one way: If encoding scheme
works in only one direction (on single circuit):
 Devices must take turns using that circuit or …
 Devices must use different circuits for each direction.
 Half-duplex transmissions take turns: Node1 sends while
Node2 listens; when Node1 finishes, Node2 sends while
Node1 listens.
 Full duplex transmissions can send/receive
simultaneously: Both endpoints can send at same time
because they use multiple wire pairs.
Full Duplex Using Two Pair, One for Each Direction
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Figure 4-13
Sending Bits with Electricity and Copper
Wires: Problems with Electricity
 Noise: Electro-Magnetic Interference (EMI)
 Cables help prevent effects of EMI in many ways, including
shielding.
 Twisting of wire pairs creates “cancellation” effect to help stop
EMI effect.
 Attenuation: Signals fade away over distance to point
where devices can’t interpret individual bits
 Ethernet standards limit copper links to 100 meters.
 Very important when designing network.
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Sending Bits with Electricity and Copper
Wires: Unshielded Twisted Pair (UTP)
 10Base-T, 100Base-T & 1000Base-T uses Unshielded
Twisted Pair (UTP).
 Cable contains twisted pairs of wires and no added
shielding materials.
 Twisting reduces EMI effects between pairs in same
jacket and in nearby cables.
 Lack of shielding makes cables less expensive, lighter,
easier to install.
 Supports full-duplex.
Note: Twisted pair cables with shielding are called
Shielded Twisted Pair (STP).
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Note
Baseband transmission of a digital signal
that preserves the shape of the digital
signal is possible only if we have a lowpass channel with an infinite or very wide
bandwidth.
2.20
Figure 3.18 Baseband transmission
2.21
Sending Bits with Electricity and Copper
Wires: LAN Standards Progression
 Ethernet has long history (developed in 1970s and is
still used today).
 IEEE standardized Ethernet in 802.3 standard in early
1980s.
 Has added many more Ethernet standards since then.
 Each standard took years to grow in marketplace and
eventually drive prices down.
Timeline of the Introduction of Ethernet Standards
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Figure 4-14
Transmission medium and physical layer
Classes of transmission media
Sending Bits with Electricity and Copper
Wires: Unshielded Twisted Pair (UTP)
 10Base-T, 100Base-T & 1000Base-T uses Unshielded
Twisted Pair (UTP).
 Cable contains twisted pairs of wires and no added
shielding materials.
 Twisting reduces EMI effects between pairs in same
jacket and in nearby cables.
 Lack of shielding makes cables less expensive, lighter,
easier to install.
 Supports full-duplex.
Note: Twisted pair cables with shielding are called
Shielded Twisted Pair (STP).
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Twisted-pair cable
UTP and STP cables
UTP connector
Sending Bits with Electricity and Copper
Wires: RJ-45 Connectors, Ports
 Ethernet standards allow use of RJ-45 connectors on
twisted pair cable and matching RJ-45 ports (sockets)
on NICs, switch ports, and other devices.
 Again, RJ-45 connectors
and ports accommodate
8 wires (pins) in single row.
Example RJ-45 Connectors and Sockets
Figure 4-15
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Sending Bits with Electricity and Copper
Wires: Cable Pinouts
Straight-through: Each wire connects to the same pin
number on both ends of the cable.
Conceptual Drawing of Straight-Through Cable
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Figure 4-17
Sending Bits with Electricity and Copper
Wires: Cable Pinout Standards
 Ethernet uses TIA (Telecommunications Industry
Association) standards to define specific wires to use for
pinouts.
 UTP cables have four pairs of wires, each using a different
color: green, blue, orange, brown.
 Each pair has 1 wire with solid color and other one with white
stripe.
TIA Cable Pinouts – T568A On Each End Creates a Straight-Through Cable
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Figure 4-18
Sending Bits with Electricity and Copper
Wires: Cable Pinout Standards—568A/568B
NOTE: 568B switches green and orange wires.
TIA Cable Pinouts – T568A On Each End Creates a Straight-Through Cable
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Figure 4-18
Figure 7.7 Coaxial cable
2.33
Break
Take 15
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Sending Bits with Light and Fiber Optic
Cables
 Fiber optics transmission like turning light switch on and
off: ON = 1, OFF = 0.
 Endpoints agree to use same speed and same basic
encoding scheme.
Encoding Bits Using Light On/Off
Figure 4-20
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Sending Bits with Light and Fiber Optic
Cables
 Fiber cables contain several parts that wrap around
glass or plastic fiber core.
 Core is about as thin as
human hair.
 Fiber breaks easily without
some type of support.
 Core and cladding have direct effect on how light
travels down cable.
 Optical transmitter (laser or LED) shines light into core
to transmit data.
Components of a Fiber Optic Cable
Figure 4-21
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Optical fiber
Figure 7.12 Propagation modes
2.38
Wireless transmission waves
Sending Bits with Radio Waves and No
Cables: Radio Basics
A Radio Station Broadcasting a Radio Signal to a Car Radio
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Figure 4-28
Figure 16.1 Cellular system
Typical Radius = 1-12 mile
9.41
Mobile phone Standard
• GSM: Global System for Mobiles
• CDMA: Code Division Multiple Access
• UMTS: Universal Mobile Telephone
System
Sending Bits with Radio Waves and No
Cables: WLAN IEEE Standards
IEEE WLAN
Standard
Maximum
Stream Rate
(Mbps)
Number of NonFrequency
overlapping
Range
Channels
802.11b
11
2.4 GHz
3
802.11a
54
5 GHz
23
802.11g
54
2.4 GHz
3
802.11n
72
5 GHz
21
802.11n*
150
5 GHz
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802.11ac**
1000 Plus
5 GHz
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• * When using bonded 40 MHz channel, instead of 20 MHz channel (as used by other
standards outlined in table).
• ** http://www.radio-electronics.com/info/wireless/wi-fi/ieee-802-11ac-gigabit.php
WLAN Standards and Speeds
Table 4-4
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Unit 4 Assignment
• Complete the following tasks using the
Chapter Review Activities at the end of
Chapter 4 in the Odom textbook (answers
can be found in the textbook):
• Respond to the multiple-choice questions.
• Complete the Define Key Terms table.
Lab and Project
• Assignment Unit 4 Assignment 1: Physical
Layer Network Concepts Review
• Unit 4 Lab 4.1: Copper Cabling
• Unit 4 Lab 4.2: Data Link Connections
• Unit 4 Lab 4.3: Cabling Exploration
• Unit 4 Lab 4.4: Cable Troubleshooting
• Unit 4 Research Project 1: Chapter 5 Mind
Maps