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CWNA Guide to Wireless LANs, Second Edition

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Title: CWNA Guide to Wireless LANs, Second Edition


1
CWNA Guide to Wireless LANs, Second Edition
  • Chapter Two
  • Wireless LAN Devices and Standards

2
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

3
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

4
WLAN Devices Wireless Network Interface Card
Figure 2-1 Network interface card for a wired
network
5
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
6
WLAN Devices Wireless Network Interface Card
Figure 2-3 Wireless NICs for laptop computers
(a) CardBus card (b) Mini PCI card
7
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

8
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

9
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

10
WLAN Devices Access Point
Figure 2-6 An access point acts as a bridge
between the wireless network and a wired network
11
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

12
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

13
WLAN Devices Remote Wireless Bridge
Figure 2-8 Point-to-point remote wireless bridge
14
WLAN Devices Remote Wireless Bridge
Figure 2-9 Point-to-multipoint remote wireless
bridge
15
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

16
WLAN Devices Remote Wireless Bridge
Figure 2-10 Root and non-root modes
17
WLAN Devices Remote Wireless Bridge
Figure 2-11 Repeater mode
18
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

19
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

20
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

21
Advantages and Disadvantages of Standards
Table 2-1 Advantages and disadvantages of
standards
22
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

23
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

24
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

25
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)

26
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

27
Institute of Electrical and Electronics Engineers
(continued)
Table 2-2 Current IEEE 802 committees
28
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

29
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

30
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

31
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

32
FCC Regulating the Radio Frequency Spectrum
Table 2-3 Common radio frequency bands
33
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

34
FCC Regulating the Radio Frequency Spectrum
Table 2-4 Unlicensed bands
35
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

36
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

37
IEEE 802.11 (continued)
Figure 2-13 Directed transmission
38
IEEE 802.11 (continued)
Figure 2-14 Diffused transmission
39
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

40
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

41
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

42
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

43
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

44
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

45
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

46
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
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