Download CIS 1140 Network Fundamentals

CIS 1140 Network Fundamentals
Chapter 8 Wireless
Networking
Collected and Compiled
By JD Willard
MCSE, MCSA, Network+,
Microsoft IT Academy Administrator
Computer Information Systems Instructor
Albany Technical College
Attention: Accessing Demos
• This course presents many demos.
• The Demos require that you be logged in to the Virtual
Technical College web site when you click on them to run.
• To access and log in to the Virtual Technical College web site:
– To access the site type www.vtc.com in the url window
– Log in using the username: CIS 1140 or ATCStudent1
– *Enter the password: student
• If you should click on the demo link and you get an Access
Denied it is because you have not logged in to vtc.com or you
need to log out and log back in.
*Remember that passwords are case sensitive so enter it in all lower case
letters.
Objectives
• Explain how nodes exchange wireless signals
• Identify potential obstacles to successful wireless
transmission and their repercussions, such as
interference and reflection
• Understand WLAN (wireless LAN) architecture
• Specify the characteristics of popular WLAN
transmission methods, including 802.11 a/b/g/n
• Install and configure wireless access points and their
clients
• Describe wireless MAN and WAN technologies,
including 802.16 and satellite communications
Wireless Basics Demo
Wireless Transmission
• Networks that transmit signals through the atmosphere via infrared or RF waves are
known as wireless networks or wireless LANs (WLANs)
• Computers communicate using standard networking protocols, but without the use of
cabling to connect devices
• The computers transmit data by means of wireless signals produced by infrared
(requiring equipment to be in a direct line of sight) or radio waves
• Wireless networks require installation of NICs with built-in antennas and uses access
points as hubs
• Wireless networks use the 2.4-2.4835 GHz frequency range
Introduction Demo
Wireless Hardware Overview Demo
The Wireless Spectrum
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Continuum of
electromagnetic waves
– Data, voice
communication
– Arranged by
frequencies
• Lowest to highest
– Spans 9 KHz and 300
GHz
Wireless services associated
with one area
Most cordless telephones
and many wireless LANs use
frequencies around 2.4 GHz.
FCC oversees United States
frequencies
ITU oversees international
frequencies
– Air signals propagate
across borders
Characteristics of Wireless Transmission
•Wireless signals originate from electrical
current traveling along a conductor
•The signal travels from the transmitter to
an antenna, which emits the signal, as a
series of electromagnetic waves, to the
atmosphere
•The signal propagates through the air
until it reaches its destination
•At the destination, another antenna
accepts the signal, and a receiver
converts it back to current
Characteristics of Wireless Transmission
• Similarities with wired
– Layer 3 and higher protocols
– Signal origination
• From electrical current, travel along conductor
• Differences from wired
– Signal transmission
• No fixed path, guidance
• Antenna
– Signal transmission and reception
– Same frequency required on each antenna
• Share same channel
Wireless Vs Wired Networks Demo
Characteristics of Wireless Transmission
Wireless transmission and reception
Antennas
• Radiation pattern describes relative strength over
three-dimensional area of all electromagnetic energy
the antenna sends or receives
• Directional antenna issues wireless signals along a
single direction
• Omnidirectional antenna issues and receives wireless
signals with equal strength and clarity in all
directions
• Range: geographical area an antenna or wireless
system can reach, generally about 100m
Antennas Demo
Signal Propagation
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LOS (line-of-sight)
– Signal travels
• In straight line, directly from transmitter
to receiver
Obstacles affect signal travel
– Pass through them
– Absorb into them
– Subject signal to three phenomena
• Reflection: bounce back to source
• Diffraction: splits into secondary waves
• Scattering: diffusion in multiple
different directions
Multipath signals
– Wireless signals follow different paths to
destination
– Caused by reflection, diffraction, scattering
– Advantage
• Better chance of reaching destination
– Disadvantage
• Signal delay
Multipath signal propagation
Signal Degradation
• Fading
– Change in signal strength
• Electromagnetic energy scattered, reflected, diffracted
• Attenuation
– Signal weakens
• Moving away from transmission antenna
– Correcting signal attenuation
• Amplify (analog), repeat (digital)
• Noise
– Significant problem
• No wireless conduit, shielding
Frequency Ranges
• 2.4-GHz band (older)
– Frequency range: 2.4–2.4835 GHz
– 11 unlicensed communications channels
– Susceptible to interference
• Unlicensed
– No FCC registration required
• 5-GHz band (newer)
– Frequency bands
• 5.1 GHz, 5.3 GHz, 5.4 GHz, 5.8 GHz
– 24 unlicensed bands, each 20 MHz wide
– Used by weather, military radar communications
Narrowband, Broadband, and Spread Spectrum
Signals
• Narrowband: transmitter concentrates signal energy at single frequency or
in very small range of frequencies
• Broadband: uses relatively wide band of wireless spectrum
– Offers higher throughputs than narrowband
• Spread spectrum: use of multiple frequencies to transmit a signal which
offers security
• FHSS (frequency hopping spread spectrum)
– Signal jumps between several different frequencies within band
– Synchronization pattern known only to channel’s receiver, transmitter
• DSSS (direct-sequence spread spectrum)
– Signal’s bits distributed over entire frequency band at once
– Each bit coded
• Receiver reassembles original signal upon receiving bits
Wireless Transmission Methods Demo
Fixed versus Mobile
• Fixed communications wireless systems
– Transmitter, receiver locations do not move
– Transmitting antenna focuses energy directly toward
receiving antenna
• Point-to-point link results
– Advantage
• No wasted energy issuing signals
• More energy used for signal itself
• Mobile communications wireless systems
– Receiver located anywhere within transmitter’s range
• Receiver can roam
Wireless LAN (WLAN) Architecture
• Ad hoc WLAN
– Wireless nodes
transmit directly to
each other
– Use wireless NICs
• No intervening
connectivity device
– Poor performance
• Many spread out
users, obstacles
block signals
• Access point (AP)
– Accepts wireless
signals from multiple
nodes
• Retransmits signals
to network
An ad-hoc WLAN
Wireless Topologies Demo
– Base stations,
wireless routers,
wireless gateways
Wireless LAN Architecture
• Infrastructure Mode
WLAN
– Stations communicate
with access point
• Not directly with each
other
– Access point requires
sufficient power,
strategic placement
• WLAN may include
several access points
– Dependent upon
number of stations
– Maximum number
varies: 10-100
An infrastructure WLAN
Wireless LAN Architecture
•A WAP works as a
wireless bridge to connect
the wireless nodes to the
wired network
•A WAP must be
strategically located so that
stations can communicate
with it
•The maximum number of
stations each access point
can server varies from 10
to 100
•Stations must stay within
the range of a WAP,
generally 300 feet or 100
meters
Wireless LAN interconnection
Wireless Access Points Demo
WLAN Architecture
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Mobile networking allows
roaming wireless nodes
– Range dependent upon
wireless access method,
equipment manufacturer,
office environment
• Access point range:
300 feet maximum
Can connect two separate
LANs
– Fixed link, directional
antennas between two
access points
• Allows access points
1000 feet apart
Support for same protocols,
operating systems as wired
LANs
– Ensures compatibility
Wireless LAN interconnection
802.11 WLANs
• Wireless technology
standard
– Describes unique
functions
• Physical and Data Link
layers
– Differences
• Specified signaling
methods, geographic
ranges, frequency usages
– Developed by IEEE’s
802.11 committee
• Wi-Fi (wireless fidelity)
standards
– 802.11b, 802.11a,
802.11g, 802.11n (draft)
– Share characteristics
• Half-duplexing, access
method, frame format
Radio Frequency Networking Demo
Wireless Networking Standards Demo
Wireless Networks: 802.11
A WLAN with multiple access points
Access Method
• 802.11 MAC services
– Append 48-bit (6-byte) physical addresses to frame
• Identifies source, destination
• Same physical addressing scheme as 802.3
– Allows easy combination
• Wireless devices
– Not designed for simultaneous transmit, receive
– Cannot quickly detect collisions
– Use different access method
• CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance)
– Minimizes collision potential
– Uses ACK packets to verify every transmission
• Requires more overhead than 802.3
• Real throughput less than theoretical maximum
• RTS/CTS (Request to Send/Clear to Send) protocol
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Optional
Ensure packets not inhibited by other transmissions
Efficient for large transmission packets
Further decreases overall 802.11 efficiency
Association
• Packet exchanged between computer, access
point
– Gain Internet access
• Scanning
– Surveying surroundings for access point
– Active scanning transmits special frame
• Probe
– Passive scanning listens for special signal
• Beacon fame
• SSID (service set identifier)
– Unique character string used to identify an
access point
• In beacon fame information
– Configured in access point
– Better security, easier network management
• BSS (basic service set)
– Station groups sharing access point
– BSSID (basic service set identifier)
• Station group identifier
A network with a single BSS
Association
•
ESS (extended service set)
– Access point group connecting same LAN
•
Share ESSID (extended service set identifier)
– Allows roaming
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Station moving from one BSS to another without
losing connectivity
Several access points detected
– Select strongest signal, lowest error rate
– Poses security risk
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Powerful, rogue access point
ESS with several authorized access points
– Must allow station association with any access
point
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While maintaining network connectivity
Reassociation
– Mobile user moves from one access point’s range
into another’s range
– Occurs by simply moving, high error rate
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Stations’ scanning feature
– Used to automatically balance transmission loads
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Between access points
A network with multiple BSSs forming
an ESS
Frames
•
802.11 networks overhead
– ACKs, probes, beacons
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802.11 specifies MAC sublayer frame type
Multiple frame type groups
– Control: association and reassociation
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Probe, beacon frames
– Management: medium access, data delivery
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ACK and RTS/CTS frames
– Data: carry data sent between stations
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802.11 data frame overhead
– Four address fields
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Source address, transmitter address, receiver address, destination address
– Sequence Control field
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How large packet fragmented
– Frame Control field
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Wi-Fi share MAC sublayer characteristics
Wi-Fi differ in modulation methods, frequency, usage, ranges
Basic 802.11 data frame
802.11b
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802.11b also know as Wi-Fi for Wireless Fidelity
The oldest and least expensive wireless standard
Compatible with 802.11g and being replace by 802.11g
Uses Direct Sequence Spread Spectrum signaling in the 2.4-GHz band
Theoretical maximum throughput of 11Mbps; actual throughput
typically around 5Mbps
Nodes must stay within 100 meters of an access point
802.11b Wireless Local Area Networks (WLANs) support three nonoverlapping or non-interfering channels that can be used in a single
area
The Wireless Access Points or bridges must use non-adjacent, nonoverlapping radio channels to prevent interference from the adjacent
bridge or Access Point
When using multiple bridges to cover a large area, you should ensure
that the channels are configured in such a way that there is no
overlapping
802.11b Demo
802.11a
• Released after 802.11b
• 802.11a differs from 802.11b and 802.11g in that it uses multiple
frequency bands in the 5GHz range
• Not congested like 2.4-GHz band
– Lower interference, requires more transmit power
• Provides a maximum theoretical throughput of 54Mbps, though its
effective throughput falls generally between 11 and 18Mbps
• Attributable to higher frequencies, unique modulating data method,
more available bandwidth
• The average geographic range for an 802.11a antenna is 20 meters,
or approximately 66 feet
• As a result, 802.11a networks require a greater density of access
points between the wire-bound LAN and wireless clients to cover
the same distance that 802.11b networks cover
• More expensive than either 802.11b or 802.11g
• Not compatible with either 802.11b and 802.11g
802.11a Demo
802.11g
• 802.11g is just as affordable as 802.11b
• A maximum theoretical throughput of 54Mbps
through different encoding techniques
• The effective throughput ranges generally from 20 to
25 Mbps
• Its geographic range is 100 meters or 328 feet
• 802.11b and 802.11g NICs and WAPs can be mixed
into the same network
• 802.11g uses the 2.4-GHz frequency band making it
compatible with 802.11b networks
802.11g Demo
802.11n
• Draft: expected ratification in late 2009
• Manufacturers
– Selling 802.11n-compatible transceivers
• Primary goal
– Wireless standard providing much higher effective throughput
• Maximum throughput: 600 Mbps
– Threat to Fast Ethernet
• Backward compatible with 802.11a, b, g standards
• May use either the 2.4-GHz or 5-GHz frequency range.
• Compared with 802.11a, 802.11g
– Same data modulation techniques
• Compared with three 802.11 standards
– Manages frames, channels, encoding differently
• Allows high throughput
802.11n Demo
802.11n
• MIMO (multiple input-multiple output)
– Multiple access point antennas may issue signal
to one or more receivers
– Increases network’s throughput, access point’s
range
• Channel bonding
– Two adjacent 20-MHz channels bonded to make
40-MHz channel
• Doubles the bandwidth available in single 20-MHz
channel
• Bandwidth reserved as buffers assigned to carry data
• Higher modulation rates
– Single channel subdivided into multiple, smaller
channels
• More efficient use of smaller channels
• Different encoding methods
802.11n access point
with three antennas
802.11n
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Frame aggregation
– Combine multiple frames into one larger frame
– Advantage: reduces overhead
Aggregated 802.11n frame
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Maximum throughput dependencies
– Number, type of strategies used
– 2.4-GHz or 5-GHz band
– Actual throughput: 65 to 600 Mbps
Backward compatible
– Not all 802.11n features work
Recommendation
– Use 802.11n-compatible devices
Bluetooth
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Bluetooth is a short-range radio technology aimed at creating a very easy to set up, small in nature, wireless
network. It’s normally used for mobile devices sharing a close proximity. Wireless mice and keyboards
commonly use Bluetooth.
Ericson’s original goals
– Wireless technology compatible with multiple devices
– Require little power
– Cover short ranges
Aim of Bluetooth Special Interest Group (SIG)
– Refine and standardize technology
– Result: Bluetooth
• Mobile wireless networking standard using FHSS (frequency hopping spread spectrum) RF signaling
in 2.4-GHz band
Version 1.1
– Maximum theoretical throughput: 1 Mbps
– Effective throughput: 723 Kbps
– 10 meter node difference
– Designed for PANs (personal area networks)
Version 2.0 (2004)
– Different encoding schemes
• 2.1-Mbps throughput
– communicating nodes can be as far as 30 meters apart
– Usage: cellular telephones, phone headsets, computer peripherals, PDAs
Overview of Bluetooth Demo
Summary of WLAN Standards
Wireless standards
Implementing a WLAN
• Designing a small WLAN
– Home, small office
• Formation of larger, enterprise-wide WANs
• Installing and configuring access points and
clients
• Implementation pitfalls
– Avoidance
• Material applies to 802.11b and 802.11g
– Most popular
Determining the Design
• One access point
– Combine with switching,
routing functions
– Connects wireless clients
to LAN
– Acts as Internet gateway
• Access point WLAN
placement
considerations
– Typical distances
between access point
and client
– Obstacles
• Type, number between
access point and clients
Determining the Design
• Larger WLANs
– Systematic approach to access
point placement
• Site survey
– Assesses client requirements,
facility characteristics, coverage
areas
– Determines access point
arrangement ensuring reliable
wireless connectivity
• Within given area
– Proposes access point testing
• Testing wireless access from
farthest corners
• Install access points
– Must belong to same ESS, share
ESSID
• Enterprise-wide WLAN design
considerations
– How wireless LAN portions will
integrate with wired portions
Enterprise-wide WLAN
Site Survey & Design Demo
Configuring Wireless Connectivity Devices
• Netgear WGR614 (v7)
– Popular, low-cost access point
– Four switch ports, routing capabilities
– Supports 802.11b, 802.11g transmission
• Configuration steps on other small wireless
connectivity devices
– Differ somewhat
– Follow similar process, modify same variables
Configure WAP Demo
The Netgear router Basic Settings page
Netgear router Wireless Settings page
The Netgear router Advanced Wireless Settings page
The Netgear router LAN IP Setup page
The Netgear router Router Status page
Wireless Router Re-Configuration
• If something goes awry during your wireless router
configuration, you can force all of the variables you
changed to be reset.
• Wireless routers feature a reset button on their back
panel.
• To reset the wireless router, first unplug it.
• Then, using the end of a paperclip, depress the reset
button while you plug it in.
• Continue holding down the button for at least 30
seconds (this time period varies among manufacturers;
check your wireless router’s documentation for the
duration yours requires).
• At the end of this period, the wireless router’s values
will be reset to the manufacturer’s defaults.
Configuring Wireless Clients
• Configuration varies from one client type to
another
• Windows XP client WLAN configuration
– Use graphical interface
• Linux and UNIX clients wireless interface
configuration
– Use graphical interface
– iwconfig is a command-line function for
viewing and setting wireless interface parameters
and it is common to nearly all versions of Linux
and UNIX
Configuring Wireless Clients
Windows XP Wireless Network
Connection Properties dialog box
Windows XP Wireless network
properties dialog box
Configure Wireless client Demo
Configuring Wireless Clients
Output from iwconfig command
Avoiding Pitfalls
• Access point versus client configurations
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SSID mismatch
Incorrect encryption
Incorrect channel, frequency
Standard mismatch (802.11 a/b/g/n)
• Incorrect antenna placement
– Verify client within 330 feet
• Interference
– Because wireless signals cannot depend on a conduit or
shielding to protect them from extraneous EMI, they are more
vulnerable to noise.
– The extent of interference depends partly on the density of
signals within a geographical area.
– If intermittent and difficult-to-diagnose wireless communication
errors occur, interference might be the culprit.
– Check for EMI sources
Wireless WANs and Internet Access
• Wireless broadband
– Latest wireless WAN technologies
– Specifically designed for:
• High-throughput, long-distance digital data exchange
802.11 Internet Access
• Access points: 802.11b or 802.11g access
methods
• Hot spots
– Places with publicly available wireless Internet access
– Free or subscription
• Hot spot subscription Internet access
– Log on via Web page
– Client software managing client’s connection
• Network log on, secure data exchange
• Added security: accept connection based on MAC address
• Accept user’s connection based on MAC address
802.16 (WiMAX) Internet Access
•
WiMAX (Worldwide Interoperability for Microwave Access)
– Current version: 802.16e (2005)
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Improved mobility, QoS characteristics
Digital voice signals, mobile phone users
Functions in 2 and 66 GHz range
– Licensed, nonlicensed frequencies
•
line-of-sight paths between antennas
– Throughput potential maximized
•
Non-line-of-sight paths
– Exchange signals with multiple stations at once
•
Two distinct advantages over Wi-Fi
– Much greater throughput (70 Mbps)
– Much farther range (30 miles)
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Appropriate for MANs and WANs
Highest throughput achieved over shortest distances between transceivers
Possible uses
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Alternative to DSL, broadband cable
Well suited to rural users
Internet access to mobile computerized devices
Residential homes
Residential WiMAX Installation
• In residential WiMAX the carrier installs a
small antenna on the homeowner’s roof
or chimney or even inside the house.
– This antenna is connected to a device
similar to a cable or DSL modem for
clients to access the LAN.
– The connectivity device could be
incorporated along with the antenna in
the same housing or might be separate.
– If separate, the device typically attaches
to the antenna with coaxial cable.
– It’s often combined with a router.
• The homeowner’s antenna
communicates in a non-line-of-sight
fashion with the service provider’s
antenna.
– If the service provider’s facility is far
away, it might use multiple antennas on
towers that communicate in a line-ofsight manner.
WiMAX
residential
antenna
802.16 (WiMAX) Internet Access
• Metropolitan area installation
– Home antenna, connectivity device
eliminated
• WiMAX MANs
– Extensive connectivity
– Download data rates faster than home
broadband connection
– Shared service
• Apportioned bandwidth
• Drawback
– Expensive
WiMAX service
provider’s
antenna
Satellite Internet Access
• Used to deliver:
– Digital television and radio signals
– Voice and video signals
– Cellular and paging signals
• Provides homes and businesses with Internet
access
Satellite Orbits
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Geosynchronous orbit
– Geosynchronous orbiting
satellites are the type
used by the most popular
satellite Internet access
service providers
– Satellites orbit the Earth
at the same rate as the
Earth turns
– Downlink
• Satellite transponder
transmits signal to
Earth-based receiver
– Typical satellite
• 24 to 32 transponders
• Unique downlink
frequencies
LEO (low Earth orbiting)
satellites
– Orbit Earth with altitude
100 miles to 1240 miles
– Not positioned over
equator
•
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MEO (medium Earth orbiting) satellites
– Orbit Earth 6000 to 12,000 miles above surface
– Not positioned over equator
• Latitude between equator and poles
– Advantage
• Cover larger Earth surface area than LEO
satellites
• Less power, less signal delay than GEO
satellites
Geosynchronous orbiting satellites most popular for
satellite Internet access
Satellite Frequencies
• Five frequency bands
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L-band—1.5–2.7 GHz
S-band—2.7–3.5 GHz
C-band—3.4–6.7 GHz
Ku-band—12–18 GHz
Ka-band—18–40 GHz
• Within bands
– Uplink, downlink transmissions differ
• Satellite Internet access providers typically use
frequencies in the C- or Ku- bands.
– Ka-band (future)
Satellite Internet Services
• Subscriber
– Small satellite dish antenna,
receiver
– Exchanges signals with provider’s
satellite network
• Satellite Internet access service
– Dial return arrangement
(asymmetrical)
• Receives Internet data via downlink
transmission
• Sends data to satellite via analog
modem connection
– Satellite return arrangement
(symmetrical)
• Send, receive data to and from
Internet using satellite uplink and
downlink
• Upstream and downstream
throughputs are advertised to reach
400–500 Kbps.
– In reality, throughputs are often
higher
Dial return satellite Internet service
Summary
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WLAN Architecture characteristics
Popular WLAN Physical, Data Link layer standards
Wireless signal exchange
Small WLAN considerations
Larger, enterprise-wide WAN formation
Installing, configuring access points, clients
WLAN Pitfalls
MANs, WANs wireless transmission
Satellite Internet Access characteristics