CWNA Guide to Wireless LANs, Second Edition

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CWNA Guide to Wireless LANs, Second Edition

• Chapter Two
• Wireless LAN Devices and Standards

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Objectives

• List WLAN devices and describe their basic
  functions
• Explain the different types of communication
  standards and why standards are important
• List the three major wireless standards and
  regulatory agencies and their functions
• Describe the different IEEE WLAN standards

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WLAN Devices Wireless Network Interface Card

• Network interface card (NIC) Connects computer
  to network so that it can send and receive data
• Wireless NICs perform same function, but without
  wires
• When wireless NICs transmit
• Change computers internal data from parallel to
  serial transmission
• Divide data into packets and attach sending and
  receiving computers address
• Determine when to send packet
• Transmit packet

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WLAN Devices Wireless Network Interface Card
Figure 2-1 Network interface card for a wired
network
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WLAN Devices Wireless Network Interface Card
Figure 2-2 Wireless NICs for desktop computers
(a) PCI network interface card, (b) standalone
USB device, (c) USB key fob
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WLAN Devices Wireless Network Interface Card
Figure 2-3 Wireless NICs for laptop computers
(a) CardBus card (b) Mini PCI card
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WLAN Devices Wireless Network Interface Card

• For smaller devices, several options
• CardBus or Type II PC Card
• May require a sled
• CompactFlash (CF) card Consists of small circuit
  board containing flash memory chips and dedicated
  controller chip
• These are small and consume little power
• SDIO (Secure Digital I/O) or SDIO NOW! Card
  Provides high-speed data input/output with low
  power consumption

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WLAN Devices Wireless Network Interface Card

• A movement towards integrating wireless NICs
• Would eliminate need for external wireless NICs
• Software drivers necessary to allow wireless NIC
  and operating system (OS) to interface
• Windows XP and PDA OSs have built-in drivers

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WLAN Devices Access Point

• Three major parts
• Antenna and radio transmitter/receiver
• RJ-45 wired network interface
• Special bridging software
• To interface wireless devices to other devices
• Two basic functions
• Base station for wireless network
• Bridge between wireless and wired networks

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WLAN Devices Access Point
Figure 2-6 An access point acts as a bridge
between the wireless network and a wired network
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WLAN Devices Access Point

• Range depends on several factors
• Type of wireless network supported
• Walls, doors, and other solid objects
• Number of wireless clients that single AP can
  support varies
• Theoretically over 100 clients
• No more than 50 for light network use
• No more than 20 for heavy network use
• Power over Ethernet (PoE) Power delivered to AP
  through unused wires in standard unshielded
  twisted pair (UTP) Ethernet cable

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WLAN Devices Remote Wireless Bridge

• Bridge Connects two network segments together
• Even if they use different types of physical
  media
• Remote wireless bridge Connects two or more
  wired or wireless networks together
• Transmit at higher power than WLAN APs
• Use directional antennas to focus transmission in
  single direction
• Delay spread Minimize spread of signal so that
  it can reach farther distances
• Have software enabling selection of clearest
  transmission channel and avoidance of noise and
  interference

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WLAN Devices Remote Wireless Bridge
Figure 2-8 Point-to-point remote wireless bridge
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WLAN Devices Remote Wireless Bridge
Figure 2-9 Point-to-multipoint remote wireless
bridge
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WLAN Devices Remote Wireless Bridge

• Four modes
• Access point mode Functions as standard AP
• Root mode Root bridge can only communicate with
  other bridges not in root mode
• Non-root mode Can only transmit to another
  bridge in root mode
• Repeater mode Extend distance between LAN
  segments
• Placed between two other bridges
• Distance between buildings using remote wireless
  bridges can be up to 18 miles at 11 Mbps or 25
  miles transmitting 2 Mbps

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WLAN Devices Remote Wireless Bridge
Figure 2-10 Root and non-root modes
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WLAN Devices Remote Wireless Bridge
Figure 2-11 Repeater mode
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WLAN Devices Wireless Gateway

• Combines wireless management and security in
  single appliance
• Authentication
• Encryption
• Intrusion detection and malicious program
  protection
• Bandwidth management
• Centralized network management

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Understanding Standards

• Standards make it easier to purchase and use wide
  variety of products
• Wireless technology based on standards
• Standards help ensure different products from
  different vendors function in same capacity

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The Need for Standards

• Standards for telecommunications have been
  essential since very beginning
• Without standards telecommunications would
  essentially be impossible
• Some IT professionals believe that standards have
  stifled growth in the field
• Waiting for standards to catch up to changes
  slows down process of change and development
• In reality, standards have proven to be more
  beneficial than harmful

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Advantages and Disadvantages of Standards
Table 2-1 Advantages and disadvantages of
standards
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3 Types of Standards

• De Facto, De jure and Consortia
• De facto standards Common practices that the
  industry follows for various reasons
• Ranging from ease of use to tradition to what
  majority of users do
• Usually established by success in marketplace
• De jure standards Official standards
• Controlled by organization or body that has been
  entrusted with that task
• Process for creating these standards can be very
  involved

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Types of Standards (continued)

• One complaint against de jure standards is amount
  of time it takes for a standard to be completed
• Consortia Usually industry-sponsored
  organizations that want to promote a specific
  technology
• Goal is to develop a standard that promotes
  organizations specific technology in little time

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Enforcing Standards

• Marketplace itself enforces some standards
• Standards created by consortia often regulated by
  marketplace
• De jure standards often enforced by outside
  regulatory agency
• Ensure that participants adhere to prescribed
  standards
• Must have power to enforce standards and
  effectively punish those who refuse to abide by
  them

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Wireless Standards Organizations and Regulatory
Agencies

• Three primary standard-setting and regulatory
  bodies that play major role in wireless LAN
  technology
• Institute of Electrical and Electronics Engineers
  (IEEE)
• Wi-Fi Alliance
• U.S. Federal Communications Commission (FCC)

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Institute of Electrical and Electronics Engineers
(IEEE)

• Establishes standards for telecommunications
• Also covers wide range of IT standards
• Worlds largest technical professional society
• 37 Societies and Councils
• Publish technically focused journals, magazines,
  and proceedings
• Work on over 800 standards
• Best known for its work in establishing standards
  for computer networks
• Project 802
• February 1980.hence 802 802

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Institute of Electrical and Electronics Engineers
(continued)
Table 2-2 Current IEEE 802 committees
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Wi-Fi Alliance

• Wireless Ethernet Compatibility Alliance (WECA)
  Consortium of wireless equipment manufacturers
  and software providers formed to promote wireless
  network technology
• Three goals
• Encourage wireless manufacturers to use IEEE
  802.11 technologies
• Promote and market these technologies to
  consumers at home, and in small and large
  organizations
• Test and certify that wireless products adhere to
  the IEEE 802.11 standards

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Wi-Fi Alliance (continued)

• WECA changed to Wi-Fi Alliance in 2002
• Reflected name of certification that it uses
  (Wi-Fi) to verify that products follow IEEE
  standards
• Only products that pass Wi-Fi Alliance tests may
  be referred to as Wi-Fi Certified
• Wi-Fi Alliance now allows businesses to apply to
  be registered as a Wi-Fi ZONE
• Qualifies them to be placed in online database of
  wireless hotspot locations
• Can be accessed through Alliances Web site

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Federal Communications Commission (FCC)
Responsibilities

• Primary regulatory agency for wireless
  communications in U.S. and territorial
  possessions
• Independent government agency
• Directly responsible to Congress
• Broad range of responsibilities
• Develop and implement regulatory programs
• Process applications for licenses and other
  filings
• Analyze complaints
• Conduct investigations
• Take part in congressional hearings

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FCC Regulating the Radio Frequency Spectrum

• FCC regulates radio frequency spectrum
• Entire range of all radio frequencies
• Spectrum divided into 450 different bands
• U.S. obligated to comply with international
  spectrum allocations
• FCC license normally required to send and receive
  on a specific frequency
• License-exempt spectrum or unregulated bands
  Bands that are available nationwide to all users
• Created to foster development of new devices

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FCC Regulating the Radio Frequency Spectrum
Table 2-3 Common radio frequency bands
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FCC Regulating the Radio Frequency Spectrum

• Two unregulated bands used for WLANs
• Industrial, Scientific, and Medical (ISM) band
• Unlicensed National Information Infrastructure
  (U-NII) band
• Intended for devices that provide short-range,
  high-speed wireless digital communications
• Negative features of unregulated bands
• Devices from different vendors may attempt to use
  same frequency
• Can cause interference and unpredictability

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FCC Regulating the Radio Frequency Spectrum
Table 2-4 Unlicensed bands
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Types of Wireless LANs

• Since late 1990s, IEEE has approved four
  standards for wireless LANs
• IEEE 802.11
• IEEE 802.11b
• IEEE 802.11a
• IEEE 802.11g
• IEEE 802.11n expected to be approved by 2006

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IEEE 802.11

• Specified that wireless transmission could take
  place via infrared (IR) or radio signals
• Infrared Transmissions
• Can send data by the intensity of the infrared
  light wave
• Light spectrum All types of light
• Infrared light Can be used for wireless
  transmissions
• Invisible
• Emitter Device that transmits a signal
• Detector Device that receives a signal

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IEEE 802.11 (continued)
Figure 2-13 Directed transmission
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IEEE 802.11 (continued)
Figure 2-14 Diffused transmission
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IEEE 802.11 (continued)

• Infrared Transmissions (continued)
• Advantages
• Does not interfere with other communications
  signals
• Not affected by other signals
• Does not penetrate walls
• Disadvantages
• Lack of mobility
• Limited range
• Confined to indoor use
• Slow transmission speed

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IEEE 802.11 (continued)

• Radio Wave Transmissions
• Radio waves can penetrate through objects
• Provides mobility
• Radio waves travel longer distances
• Can be used indoors and outdoors
• Radio waves can travel at much higher speeds than
  infrared transmissions
• IEEE 802.11 standard outlining radio wave
  transmissions has become preferred method for
  wireless LANs

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IEEE 802.11b

• 802.11 standards 2 Mbps bandwidth not sufficient
  for most network applications
• 802.11b amendment added two higher speeds (5.5
  Mbps and 11 Mbps) to original 802.11 standard
• Uses ISM band
• Supports wireless devices up to 115 meters (375
  feet) apart
• Radio waves decrease in power over distance
• 802.11b standard specifies that, when devices out
  of range to transmit at 11 Mbps, devices drop
  transmission speed to 5.5 Mbps

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IEEE 802.11a

• IEEE 802.11a standard specifies maximum rated
  speed of 54 Mbps
• Also supports 48, 36, 24, 18, 12, 9,and 6 Mbps
  transmissions using U-NII band
• 802.11a and 802.11b published at same time
• 802.11a came to market later due to technical
  issues and high production cost
• Range of 802.11a is less than that of 802.11b

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IEEE 802.11g

• Effort to combine best features of 802.11a and
  802.11b
• Data transfer rates to 54 Mbps
• Support devices up to 115 meters apart
• 802.11g standard specifies that devices operate
  entirely in ISM frequency

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Projected IEEE 802.11n

• Currently in evaluation stage
• Top speed of 802.11n standard will be anywhere
  from 100 Mbps to 500 Mbps
• Ratification may not occur until 2006
• Devices based on standard may appear prior to
  that
• 802.11 pre-N

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Summary

• Wireless LAN devices are in many respects similar
  to those found in a wired network
• the main difference is that wireless devices use
  an antenna to send and receive signals instead of
  a wired connection
• An access point (AP) is both the base station for
  the wireless network and a bridge to connect the
  wireless network with the wired network
• A remote wireless bridge is a wireless device
  designed to connect two or more wired or wireless
  networks together

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Summary (continued)

• Standards ensure that devices from one vendor
  will interoperate with those from other vendors,
  and create competition between vendors
• There are three regulatory bodies that play a
  major role in wireless LAN technology the IEEE,
  the Wi-Fi Alliance, and the FCC
• There currently are three standards or types of
  wireless LANs IEEE 802.11b, IEEE 802.11a, and
  IEEE 802.11g