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NT1210 Introduction to Networking
Unit 4:
Chapter 4, Transmitting Bits
1
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.
2
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.
3
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
4
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
5
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)
6
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
.
Graphs of AC Circuit: Amplitude, Period, Frequency
7
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
8
Figure 4-6
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
9
Table 4-1
Frequency and period in Time
• Frequency and period are the inverse of
each other.
Comparison of analog and digital signals
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
12
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
13
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.
14
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
15
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).
18
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
22
Sending Bits with Electricity and Copper
Wires: Cable Pinouts
 Pinouts: How each wire in cable should be connected
to each pin in connector according to Ethernet
standards.
 Wires must be in correct order so correct wires in
twisted pair send to correct direction.
Wires, Connector Pin numbers, and Socket Pin Numbers
23
Figure 4-16
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
24
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
25
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
26
Figure 4-18
Figure 7.7 Coaxial cable
2.27
Break
Take 15
28
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
29
Fiber construction
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
31
Optical fiber
Figure 7.12 Propagation modes
2.33
Sending Bits with Light and Fiber Optic
Cables: Transmitters
 Key technical difference between LEDs and lasers: LEDs
shine light in multiple directions; lasers shine in one
direction.
 Fiber cables come in two major categories: Multimode
(MM), single mode (SM).
 Multimode have larger
cores and work best with LED transmitters.
 Single mode have smaller
diameter cores and work
best with laser transmitters.
LEDs with Multiple Modes (Angles), and Lasers, with a Single Mode (Angle)
34
Figure 4-24
Sending Bits with Light and Fiber Optic
Cables: Ethernet LANs
 Fiber cables do not create EMI.
 Fiber links more secure.
 Example: Typical campus
LAN has employees in two
buildings in office park that
sit 150 meters apart, which
exceeds Ethernet
standards for copper
cabling. However, multimode
links can run past 200 meters.
Typical Use of Fiber Optics in a LAN: Links Between Neighboring Buildings
35
Figure 4-25
Sending Bits with Light and Fiber Optic
Cables: WAN Links
 Synchronous Optical Network (SONET): One of longerestablished standards for WAN links.
 SONET defines series of Physical layer standards for
data transmission over
Name
(Rounded) Line Speed
optical links.
OC-1
52 Mbps
 Uses hierarchy of speeds
OC-3
155 Mbps
that are multiples of base
OC-12
622 Mbps
OC-24
1244 Mbps
speed (51.84 Mbps) plus
OC-48
2488 Mbps
some overhead.
OC-96
OC-192
4976 Mbps
9952 Mbps
SONET Optical Carrier (OC) Names and (Rounded) Line Speeds
36
Table 4-2
7-2 UNGUIDED MEDIA: WIRELESS
Unguided media transport electromagnetic waves
without using a physical conductor. This type of
communication is often referred to as wireless
communication.
Wireless transmission waves
Sending Bits with Radio Waves and No
Cables: Radio Basics
A Radio Station Broadcasting a Radio Signal to a Car Radio
39
Figure 4-28
Sending Bits with Radio Waves and No
Cables: Radio Basics
 Three facts summarize key points about why radio can
be used to wirelessly send data.
1. Radio waves have energy level that moves up and down over
time, so when graphed, waves look like sine wave.
2. Radio waves can be changed and sensed by networking
devices, including changes to frequency, amplitude, phase,
period, wavelength.
3. EM energy does not need physical medium to move.
A Radio Station Broadcasting a Radio Signal to a Car Radio
40
Figure 4-28
CELLULAR TELEPHONY
Cellular telephony is designed to provide
communications between two moving units,
called mobile stations (MSs), or between
one mobile unit and one stationary unit,
often called a land unit.
9.41
Figure 16.1 Cellular system
Typical Radius = 1-12 mile
9.42
Sending Bits with Radio Waves and No
Cables: WANs—Mobile Phones & Voice
Steps to place call on mobile phone:
1. Person speaks creating sound waves (as usual).
2. Phone converts sound waves into bits (as with all digital phones).
3. Phone sends
(encodes) bits
as radio waves
through air
towards cell
tower.
4. Radio equipment at tower receives (decodes) radio waves back into
original bits.
5. Rest of trip uses various technology (details not included here).
43
Sending Bits with Radio Waves and No
Cables: WAN Standards
Gen
2G
3G
4G
Other Terms
Standards
Related to
Body
Generation
Umbrella Standard
GSM (Global System for
TDMA, CDMA
Mobile Communications)
IMT-2000 (International
Mobile Telecommunications- UTMS
2000)
IMT-Advanced
(International Mobile
LTE, Wi-Max
Telecommunications Advanced)
Mobile Wireless Standards and Terms
ETSI
ITU
ITU, ETSI,
IEEE
Table 4-3
44
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: WLANs—Devices & Topology
 Wireless LAN devices need
WLAN Network Interface Card
(NIC).
 Gives PC ability to connect WLAN
 Uses radio antenna that allows NIC
to send and receive data
 Most WLANs use Access Points (AP) which are small
devices that acts like small radio tower.
 All wireless user devices communicate through AP.
A Small Wireless LAN with One Access Point (AP)
46
Figure 4-33
Sending Bits with Radio Waves and No
Cables: WLANs—Transmission
Wireless LANs take turns by using rules called Carrier Sense Multiple
Access with Collision Avoidance (CSMA/CA). This technology is
similar to wired Ethernet’s CSMA/CD.
CSMA/CA Process
Figure 4-37
47
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
9
802.11ac**
1000 Plus
5 GHz
12
• * 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
48
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.
Unit 4 Lab
• Complete all Labs in Chapter 4 of the lab
book.