Transcript Introduction to Networking ITT Version

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
Objectives
 Identify wireless network communication needs.
 Distinguish among the different needs for wired and
wireless networks.
 Classify Layer 2 networking components used in a
typical LAN.
 Compare and contrast advantages and disadvantages
of network media.
 Use basic troubleshooting techniques to ensure network
connectivity at Layers 1 and 2.
3
Transmitting Bits: Communication Analogy
 When two friends talk, one talks while other listens and
understands (we hope!).
 Speaker makes sounds that travel through air to
listener’s ears.
 Sounds have no meaning unless each person’s brain
works to interpret those sounds.
 In networks, nodes send data to each other over link:
Sending node acts like person talking; receiving node
acts like person listening.
4
Transmitting Bits: Communication Analogy
General idea of how a TCP/IP network forwards IP packets from one
host to another: Nodes (routers in this example) each make a choice of
where to send the packet next so the data arrives at the correct
destination. Always keep the big goal of the network in mind: Delivering
data from the source to the destination.
Sending Data Through a Network of Nodes and Links
5
Figure 4-1
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
6
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
7
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)
8
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
9
Figure 4-5
Sending Bits with Electricity and Copper
Wires: AC Frequency, Amplitude, Phase
 Most commonly used in networking encoding schemes.
 One signal used by encoding scheme means binary 0,
other means binary 1.
Encoding Options: Frequency, Amplitude, and Phase Shifts
10
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
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Table 4-1
Sending Bits with Electricity and Copper
Wires: Network Cabling
 Before a node can send data, it needs to create a circuit
between itself and the destination node.
 Copper cable has outer plastic cover (jacket) that holds
wires (conductors).
 Sending/receiving nodes use a pair
of wires connected at their ends
to create circuit.
Photo of Wires Inside a Networking Cable
Figure 4-7
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Sending Bits with Electricity and Copper
Wires: Network Cabling Example
 Cable has 4 pairs of wires: 2 used, 2 unused.
 Hardware of each node must agree which wires to use
and which to ignore.
 For wires chosen to use, nodes loop ends together to
create a circuit.
Physical Components to Create an Electrical Circuit Between Two Nodes
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Figure 4-8
Sending Bits with Electricity and Copper
Wires: Network Cabling
 Loop (circuit) can’t create circuit by itself: something has
to create electrical current.
 Transmitting node creates electrical signal, changing
signal over time to encode different bit values.
 Transmitter: Part of node that sends data.
 Receiver: Part that listens for signal of incoming bits.
Transmitter Generating a Current to Send; Receiver Sensing Current to Receive Figure 4-9
14
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 of how bit rate and encoding scheme work
together: Bit rate = 10 bps; encoding scheme states that
binary 1 should be +2 volts and binary 0 as +1 volts.
Example where Encoder Changes Signal Every Bit Time
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Figure 4-10
Sending Bits with Electricity and Copper
Wires: Encoding Scheme
 Works like language: Defines electrical equivalent of 1’s
and 0’s.
 Different frequencies represent binary 1’s and 0’s.
 Example sending 1010: Lower frequency represents
binary 1, higher frequency represents binary 0.
Frequency Shift Keying: Low Frequency = 1, High Frequency = 0
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Figure 4-11
Sending Bits with Electricity and Copper
Wires: Manchester Encoding Scheme
 Used on some early Ethernet networks.
 Does not choose one electrical signal at beginning of bit
time, instead changes signal in middle of bit time.
 Follows this logic:
 To encode 0: Start high, and
transition low in the middle of
bit time.
 To encode 1: Start low, and
transition high in the middle of
bit time.
Manchester Encoding: 0 = High-to-Low, 1 = Low-to-High
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Figure 4-12
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: Using Multiple Circuits
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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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
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
 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
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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
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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
Sending Bits with Electricity and Copper
Wires: Cable Pinout Standards
 UTP cable with four pairs (8 wires) can support four circuits.
 10Base-T and 100Base-T only use two pairs.
NOTE: 1000BaseT uses all 4 wire pairs.
 Ethernet uses following rules for creating circuits:
 One pair at pins 1 and 2
 One pair at pins 3 and 6
PC NIC Transmitting on Pair at 1,2, Receiving on Pair 3,6
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Figure 4-19
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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Sending Bits with Light and Fiber Optic
Cables
 Cladding surrounds core for entire length of cable.
 Reflects light back into core
 Light waves reflect off cladding back into core until light waves
reach other end of cable
 Fiber optic cables work well to send light in one direction at
time, but not two.
 Cable acts like
dark tunnel so
nodes can easily see light coming through cable.
 If both ends try to shine light and look for light at same time,
couldn’t tell whether light is coming from local or remote node.
Cladding Reflecting the Light Back into the Fiber Optic Cable’s Core
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Figure 4-22
Sending Bits with Light and Fiber Optic
Cables
 Instead of using one fiber cable for half-duplex
communication, most fiber links use pair of cables so
can use full-duplex.
 Each fiber NIC, port, interface, etc., has interface with
two sockets: One for send cable, one for receive cable.
 Each node’s transmit
socket must connect to
same cable as other node’s receive socket.
NOTE: In addition to sending data using light over cables, fiber
technology also includes free space optics (e.g., TV remote)
which sends light through air; requires line-of-sight.
Two Fiber Optic Cables, with Connectors
Figure 4-23
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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)
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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
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Figure 4-25
Sending Bits with Light and Fiber Optic
Cables: WAN Links
Telcos and ISPs that support WAN services use fiber optics because
they service businesses that sit far apart. To do this, Telco/ISP must
have a link from the customer to the Telco central office (CO) or ISP
Point of Presence (POP).
Two Perspectives on a Leased Line
Figure 4-26
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Sending Bits with Light and Fiber Optic
Cables: WAN Links
 Example: Fiber that connects equipment in CO to other
Telco sites (called core sites).
 COs sit at edge sites of Telco network and have links to core
sites.
 Physical locations include
office buildings with
server rooms.
 In this figure, all links use
fiber except links from
CO to customer router
which use copper.
Fiber Links Used to Help Create a Telco Network
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Figure 4-27
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
speed (51.84 Mbps) plus
OC-24
1244 Mbps
some overhead.
OC-48
2488 Mbps
OC-96
OC-192
4976 Mbps
9952 Mbps
SONET Optical Carrier (OC) Names and (Rounded) Line Speeds
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Table 4-2
Sending Bits with Radio Waves and No
Cables: Radio Basics
 Radio stations broadcast signals so anyone near enough to
station’s large antenna (radio tower) can hear broadcast.
 Radio tower sends electricity through antenna to create
radio waves.
 More electrical power creates stronger radio waves that
can travel longer distances.
 Radio tower sends signals upward because radio waves
bounce off ionosphere (one of layers of Earth’s
atmosphere).
 Bouncing radio waves off ionosphere lets radio waves
reach wider area.
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
A Radio Station Broadcasting a Radio Signal to a Car Radio
40
Figure 4-28
Sending Bits with Radio Waves and No
Cables: Radio Basics
 Electromagnetic radiation (ER): Described using
electromagnetic spectrum conceptual model
 These types of energy travel as waves, so have specific
wavelength.
 Spectrum categorizes energy based on wavelength.
 Radio waves make up one category in EM spectrum.
 Other parts include visible light, X-rays, microwaves.
 Radio waves work well for networking because can be
changed (modulated) over time to send data.
A Radio Station Broadcasting a Radio Signal to a Car Radio
41
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
42
Figure 4-28
Sending Bits with Radio Waves and No
Cables: WANs—Mobile Phones & Voice
 Mobile network provider creates
its own network.
 But most phone users want to
communicate with more phones
than just those on same mobile
company’s network, as well as
landline phones.
 Enter the Public Switched
Telephone Network (PSTN)
Major Components in the Mobile Phone Network Model
43
Figure 4-29
Sending Bits with Radio Waves and No
Cables: WANs—Mobile Phones & Voice
 Most mobile phones act as digital phones.
 Send and receive digits (bits) that represent voice traffic.
 To transmit bits, phones use wireless radio technology.
 Phone sends bits encoded as radio waves to nearby
radio antenna on tower owned by mobile phone
company.
Connecting a Mobile Phone Call through a Radio Tower to the Telco Network
44
Figure 4-30
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).
45
Sending Bits with Radio Waves and No
Cables: WANs—Mobile Phones & Data
 Radio link on phone supports data service just as it
does for voice.
 When sending or receiving data, phone passes bits
using radio waves between itself and radio tower.
 Phone encapsulates data.
 To support data applications, mobile network connects
to Internet and any other networks that support data
apps requested by user.
 Mobile network forwards data to correct destination in Internet,
not through PSTN.
Smart Phone: Using Radio to Forward Bits to the Tower, and then to the Internet Figure 4-31
46
Sending Bits with Radio Waves and No
Cables: WANs—Mobile Phones & Data
Steps in accessing Internet via mobile phone:
1. Person types URL or taps hyperlink.
2. Phone encapsulates HTTP request into IP packet, then Data Link
layer frame.
3. Phone sends (encodes) frame’s bits as radio waves towards cell
tower.
4. Radio equipment at
tower receives
(decodes) radio
waves back into
original bits.
5. Equipment near cell tower forwards bits into Internet as for any IP
packet.
47
Sending Bits with Radio Waves and No
Cables: WANs—Other Mobile Devices
 Laptops, tablets can connect to same network as
mobile phone.
 Laptops typically need wireless NIC that supplies radio
to connect to network radio towers.
 Also need contract with mobile provider for connectivity
to wireless network.
Using the Wireless WAN (Mobile Network) from Computers Instead of Phones
48
Figure 4-32
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
49
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)
50
Figure 4-33
Sending Bits with Radio Waves and No
Cables: WLANs—Devices & Topology
WLAN with AP creates a WLAN Basic Service Set (BSS). In a BSS,
all communications happen with the AP, much like it does in the
wireless WAN model.
A WLAN AP Bridges Between the WLAN and an Ethernet LAN
51
Figure 4-34
Sending Bits with Radio Waves and No
Cables: WLANs—Sending Data
For most WLAN standards, the encoding scheme uses some form of
amplitude shift keying or phase shift keying, which changes the
amplitude or phase (respectively) to represent a 0 or 1.
Amplitude and Phase Shift Basic Examples
52
Figure 4-35
Sending Bits with Radio Waves and No
Cables: WLANs—Typical Problems
 AP sits under metal desk (radio waves do not pass
through metal very well).
 AP sits next to other equipment and cables that
interfere (EMI).
 AP sits on wrong side
of interior wall
away from end
user devices.
A WLAN with Possible Sources of Interference
53
Figure 4-36
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
54
Sending Bits with Radio Waves and No
Cables: WLANs—Transmission
 Step 1: All devices use independent random wait time if
they have data to send.
 Step 2: When particular device completes its wait timer, it
sends data.
 Sender lists time it estimates is needed to send data (in
milliseconds) so other devices know how long WLAN will be in
use.
 Step 3: Receiving device shows required ACK
(acknowledgement) to confirm data received.
 Step 4: ACK triggers silence on WLAN.
CSMA/CA Process
Figure 4-37
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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
56
Sending Bits with Radio Waves and No
Cables: Example Enterprise
Many corporate campus LANs have both wired and wireless LAN support
on each floor. The WLAN connects to the same Ethernet network as the
wired network does so all devices in the two building can communicate.
Campus LAN: Wireless Devices, Wired Desktops, and Fiber Trunks
57
Figure 4-38
Summary, This Chapter…
 Looked at the details of how to move bits from one node
to the next node in a network.
 Focused on moving bits over a single link.
 Looked at how to move bits using copper wires and
electricity.
 Explained the fundamentals of how electricity can be
graphed.
 Discussed fiber optics.
 Compared and contrasted the two common types of fiber
optic transmitters and two general categories of fiber
optic cables.
58
Summary, This Chapter…
 Listed common reasons for using fiber optic cables
instead of copper cables in networks.
 Drew a diagram of the relationships between mobile
phones, mobile phone radio towers, the mobile network,
the worldwide telephone network, the Internet, home
telephones, and web servers in the Internet.
 Concluded by introducing the basics of Wireless LANs.
 Compared and contrasted mobile phones, mobile
company radio towers, wireless LAN NICs, and wireless
LAN Access Points.
 Created an example demonstrating how devices share a
wireless LAN using CSMA/CA.
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Questions? Comments?
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