Linux+ Guide to Linux Certification by wuyunqing


									        Lecture 1

Introduction to RF Fundamentals

• List WLAN devices and describe their basic
• 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

   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
• When wireless NICs transmit:
  – Change computer’s internal data from parallel to
    serial transmission
  – Divide data into packets and attach sending and
    receiving computer’s address
  – Determine when to send packet
  – Transmit packet

    WLAN Devices: Wireless Network
      Interface Card (continued)

Figure 2-1: Network interface card for a wired network
    WLAN Devices: Wireless Network
      Interface Card (continued)

Figure 2-2: Wireless NICs for desktop computers: (a) PCI network
interface card, (b) standalone USB device, (c) USB key fob
    WLAN Devices: Wireless Network
      Interface Card (continued)

Figure 2-3: Wireless NICs for laptop computers: (a) CardBus card;
(b) Mini PCI card
   WLAN Devices: Wireless Network
     Interface Card (continued)
• 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
      • Small and consume little power
   – SDIO (Secure Digital I/O) or SDIO NOW! Card:
     Provides high-speed data input/output with low
     power consumption

   WLAN Devices: Wireless Network
     Interface Card (continued)
• 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

      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 function:
   – Base station for wireless network
   – Bridge between wireless and wired networks

        WLAN Devices: Access Point

Figure 2-6: An access point acts as a bridge between the wireless
network and a wired network
      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
   WLAN Devices: Remote Wireless
• 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
     WLAN Devices: Remote Wireless
          Bridge (continued)

Figure 2-8: Point-to-point remote wireless bridge
     WLAN Devices: Remote Wireless
          Bridge (continued)

Figure 2-9: Point-to-multipoint remote wireless bridge
   WLAN Devices: Remote Wireless
        Bridge (continued)
• 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
     • 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
    WLAN Devices: Remote Wireless
         Bridge (continued)

Figure 2-10: Root and non-root modes
    WLAN Devices: Remote Wireless
         Bridge (continued)

Figure 2-11: Repeater mode
  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

        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

          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

    Advantages and Disadvantages of

Table 2-1: Advantages and disadvantages of standards
             Types of Standards

• 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

    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
  – Goal is to develop a standard that promotes
    organization’s specific technology in little time

             Enforcing Standards

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

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

 Institute of Electrical and Electronics
            Engineers (IEEE)
• Establishes standards for telecommunications
   – Also covers wide range of IT standards
• World’s largest technical professional society
   – 37 Societies and Councils
   – Publish technically focused journals, magazines, and
   – Work on over 800 standards
• Best known for its work in establishing standards
  for computer networks
   – Project 802
  Institute of Electrical and Electronics
          Engineers (continued)

Table 2-2: Current IEEE 802 committees
                   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

         Wi-Fi Alliance (continued)

• WECA changed name 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 Alliance’s Web site

• Wi-Fi™ Alliance
  – Wireless Fidelity Alliance
  – 170+ members
  – Over 350 products certified
• Wi-Fi’s™ Mission
  – Certify interoperability of WLAN products (802.11)
  – Wi-Fi™ is the “stamp of approval”
  – Promote Wi-Fi™ as the global standard

Federal Communications Commission
       (FCC): Responsibilities
• Primary regulatory agency for wireless communications in
  U.S. and territorial possessions (Canadian equivalent is the
  Canadian Radio Television and Telecommunications
   – 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

FCC: Regulating the Radio Frequency
• 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
• 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

 FCC: Regulating the Radio Frequency
        Spectrum (continued)

Table 2-3: Common radio frequency bands
FCC: Regulating the Radio Frequency
       Spectrum (continued)
• 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
• Negative features of unregulated bands:
  – Devices from different vendors may attempt to use
    same frequency
     • Can cause interference and unpredictability

 FCC: Regulating the Radio Frequency
        Spectrum (continued)

Table 2-4: Unlicensed bands
          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

                    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
   – Light spectrum: All types of light
   – Infrared light: Can be used for wireless
      • Invisible
   – Emitter: Device that transmits a signal
   – Detector: Device that receives a signal

            IEEE 802.11 (continued)

Figure 2-13: Directed transmission
            IEEE 802.11 (continued)

Figure 2-14: Diffused transmission
           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

         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

                 IEEE 802.11b
• 802.11 standard’s 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

                  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

                 IEEE 802.11g

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

                IEEE 802.11n

• Top speed of 802.11n standard will be anywhere
  from 100 Mbps to 500 Mbps

Cisco Aironet 1200


Connecting to Access Point


                       Lab 1

• 2.1,2.2,2.3,2.4 and 2.5 textbook

• 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
  or other means 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

           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 four standards or types of
  wireless LANs: IEEE 802.11b, IEEE 802.11a, IEEE
  802.11g and IEEEn


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