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CWNA Guide to Wireless LANs, Second Edition


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Title: CWNA Guide to Wireless LANs, Second Edition

CWNA Guide to Wireless LANs, Second Edition
  • Chapter One
  • Its a Wireless World

A Day in the Life of a Wireless User Home
  • Hotspots Locations where wireless data services
    are available
  • Wireless local area network (WLAN) Essentially
    identical to standard local area network (LAN)
  • Except devices not connected by wires
  • Can increase productivity

A Day in the Life of a Wireless User Car
  • Bluetooth wireless standard Enables short range
    wireless communication
  • Used in many small devices

A Day in the Life of a Wireless User Office
  • Fixed broadband wireless Wireless transmissions
    between immobile devices
  • Typically between office buildings
  • Utilizes small, customized antennas
  • Free space optics (FSO) Alternative to
    high-speed fiber optic transmissions

A Day in the Life of a Wireless User On Site
  • Radio frequency identification (RFID) tags
  • Electronic barcodes
  • Used to identify items
  • Can be read if anywhere within range of
    transmitted radio signal
  • Depending on device

Wireless Local Area Networks (WLANs)
  • Wi-Fi (Wireless Fidelity) Based on standard that
    transmits at up to 11 Mbps
  • Computers on WLAN must have wireless network
    interface cards (wireless NIC or Wireless
  • Performs same basic functions as standard NIC,
    plus more
  • Access point (AP) Transfers signals between
    wireless NICs
  • Patch cable connects AP to wired LAN or Internet

  • Low-power wireless data and voice transmission
  • Bluetooth devices communicate via radio modules
  • Link manager Software that helps identify other
    Bluetooth devices, creates links between devices,
    and sends and receives data
  • Transmit data at up to 1 Mbps over 10 meters
  • Bluetooth devices within range of each other
    automatically connect
  • Master and slave

Telecommunications Links
  • Integrated Services Digital Networks (ISDN)
    Transmits at 256 Kbps
  • T-1 lines Transmit at 1.544 Mbps
  • Cable modems Use television cable connection
  • Digital subscriber lines (DSL) Use telephone
  • WiMax Signal transmitted between antennas
  • Up to 75 Mbps and over up to 35 miles
  • Fixed Broadband

Telecommunications Links (continued)
  • FSO Transmit at speeds up to 1.25 Gbps over up
    to 4 miles
  • Line-of-site transmission

Figure 1-6 Free space optics transceiver
Cellular Telephony
  • Global Systems for Mobile (GSM) a communications
  • Coverage includes most of US and parts of Europe
    and Japan
  • Transmission speeds up to 9.6 Kbps
  • Uses Wireless Application Protocol (WAP)
  • Standard way to transmit, format, and display
    data for devices like cell phones and handheld

Cellular Telephony (continued)
Figure 1-8 Browsing the World Wide Web
Cellular Telephony (continued)
  • WAP cell phone runs a microbrowser that uses
    Wireless Markup Language (WML) instead of HTML
  • WAP gateway or proxy Translates between WML and

Figure 1-9 WAP communications
Radio Frequency Identification (RFID)
  • Like an electronic barcode
  • Can contain larger amounts of updatable
  • Information transmitted via radio waves
  • Range typically about 1 foot at 5 Mbps

Figure 1-10 RFID tag
Wireless LAN Applications Business
  • Wireless LAN technologies have significantly
    changed how business conducted
  • Meetings not confined to conference rooms
  • Easier to connect to network resources and
  • Can create office in space where traditional
    infrastructure does not exist

Wireless LAN Applications Healthcare (continued)
Figure 1-12 Video pill
Wireless Advantages and Disadvantages Advantages
  • Mobility is Primary advantage of wireless
  • Easier and Less Expensive Installation
    Installing network cabling in older buildings
    difficult and costly
  • Increased Reliability
  • eliminates certain types of cable failures and
    increases overall network reliability

Wireless Advantages and Disadvantages Advantages
  • Disaster Recovery
  • Hot site Off-site facility that can run
    businesss operations if primary site is not
  • Generally maintained by third party
  • Expensive
  • Cold site Customer provides and installs
  • Many businesses use cold sites and WLANs as major
    piece of disaster recovery plan
  • No consideration given to network cabling

Wireless Advantages and Disadvantages
  • Security Wireless signals broadcast in open air
  • Security for wireless LANs is prime concern
  • Unauthorized users might access network
  • Attackers might view transmitted data
  • Employees could install rogue access points
  • Attackers could easily crack existing wireless
  • Radio Signal Interference Signals from other
    devices can disrupt wireless transmissions
  • Health Risks Wireless devices emit RF energy
  • Not known if or to what extent low levels of RF
    might cause adverse health effects

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

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

WLAN Devices Access Point
  • Range depends on several factors
  • Type of wireless network, walls, doors, and other
    solid objects (think refrigerator)
  • 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
  • Bridge Connects two network segments together
  • Even if they use different types of physical
  • 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
  • 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

Advantages and Disadvantages of Standards
Table 2-1 Advantages and disadvantages of
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

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
    organizations 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

Wireless Standards Organizations and Regulatory
  • 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
  • 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

Institute of Electrical and Electronics Engineers
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
  • Test and certify that wireless products adhere to
    the IEEE 802.11 standards

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
  • 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

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

FCC Regulating the Radio Frequency Spectrum
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 expected to be approved by 2006

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
  • Invisible
  • Emitter Device that transmits a signal
  • Detector Device that receives a signal

IEEE 802.11 (continued)
  • Infrared Transmissions (continued)
  • Advantages
  • Does not interfere with other communications
  • 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 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

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

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
  • 802.11 pre-N

CWNA Guide to Wireless LANs, Second Edition
  • Chapter Three
  • How Wireless Works

Frequency (continued)
  • Frequency Rate at which an event occurs
  • Cycle Changing event that creates different
    radio frequencies
  • When wave completes trip and returns back to
    starting point it has finished one cycle
  • Hertz (Hz) Cycles per second
  • Kilohertz (KHz) thousand hertz
  • Megahertz (MHz) million hertz
  • Gigahertz (GHz) billion hertz

Frequency (continued)
  • Frequency of radio wave can be changed by
    modifying voltage
  • Radio transmissions send a carrier signal
  • Increasing voltage will change frequency of
    carrier signal

Analog Modulation
  • Amplitude Height of carrier wave
  • Amplitude modulation (AM) Changes amplitude so
    that highest peaks of carrier wave represent 1
    bit while lower waves represent 0 bit
  • Frequency modulation (FM) Changes number of
    waves representing one cycle
  • Number of waves to represent 1 bit more than
    number of waves to represent 0 bit
  • Phase modulation (PM) Changes starting point of
  • When bits change from 1 to 0 bit or vice versa

Antenna Concepts
  • Radio waves transmitted/received using antennas

Figure 3-24 Antennas are required for sending
and receiving radio signals
Characteristics of RF Antenna Transmissions
  • Polarization Orientation of radio waves as they
    leave the antenna

Figure 3-25 Vertical polarization
Characteristics of RF Antenna Transmissions
  • Wave propagation Pattern of wave dispersal

Figure 3-26 Sky wave propagation
Characteristics of RF Antenna Transmissions
Figure 3-27 RF Line of Sight (LOS) propagation
Antenna Types and Their Installations
  • Omni-directional antenna Radiates signal in all
    directions equally
  • Most common type of antenna
  • Semi-directional antenna Focuses energy in one
  • Primarily used for short and medium range remote
    wireless bridge networks
  • Highly-directional antennas Send narrowly
    focused signal beam
  • Generally concave dish-shaped devices
  • Used for long distance, point-to-point wireless

CWNA Guide to Wireless LANs, Second Edition
  • Chapter Four
  • IEEE 802.11 Physical Layer Standards

Figure 4-2 OSI data flow
Introduction (continued)
Table 4-1 OSI layers and functions
Wireless Modulation Schemes
  • Four primary wireless modulation schemes
  • Narrowband transmission
  • Frequency hopping spread spectrum (FHSS)
  • Direct sequence spread spectrum (DSSS)
  • Orthogonal frequency division multiplexing (OFDM)
  • Narrowband transmission used primarily by radio
  • Other three used in IEEE 802.11 WLANs

Narrowband Transmission
Figure 4-3 Narrowband transmission
Spread Spectrum Transmission
Figure 4-4 Spread spectrum transmission
Spread Spectrum Transmission
  • Advantages over narrowband
  • Resistance to narrowband interference
  • Lower power requirements
  • Less interference on other systems
  • More information transmitted
  • Increased security
  • Resistance to multipath distortion (e.g.
    reflections off of buildings and structures)

IEEE 802.11 Physical Layer Standards
  • IEEE wireless standards follow OSI model, with
    some modifications
  • Data Link layer divided into two sublayers
  • Logical Link Control (LLC) sublayer Provides
    common interface, reliability, and flow control
  • Media Access Control (MAC) sublayer Appends
    physical addresses to frames

IEEE 802.11 Physical Layer Standards (continued)
  • Physical layer divided into two sublayers
  • Physical Medium Dependent (PMD) sublayer Makes
    up standards for characteristics of wireless
    medium (such as DSSS or FHSS) and defines method
    for transmitting and receiving data
  • Physical Layer Convergence Procedure (PLCP)
    sublayer Performs two basic functions
  • Reformats data received from MAC layer into frame
    that PMD sublayer can transmit
  • Listens to determine when data can be sent

IEEE 802.11 Physical Layer Standards (continued)
Figure 4-10 Data Link sublayers
IEEE 802.11 Physical Layer Standards (continued)
Figure 4-11 PHY sublayers
IEEE 802.11b Physical Layer Standards (continued)
  • PLCP frame made up of three parts
  • Preamble prepares receiving device for rest of
  • Header Provides information about frame
  • Data Info being transmitted
  • Synchronization field
  • Start frame delimiter field
  • Signal data rate field
  • Service field
  • Length field
  • Header error check field
  • Data field

IEEE 802.11b Physical Layer Standards (continued)
  • Physical Medium Dependent Standards PMD
    translates binary 1s and 0s of frame into radio
    signals for transmission
  • Can transmit at 11, 5.5, 2, or 1 Mbps
  • 802.11b uses ISM band
  • 14 frequencies can be used
  • Two types of modulation can be used
  • Differential binary phase shift keying (DBPSK)
    For transmissions at 1 Mbps
  • Differential quadrature phase shift keying
    (DQPSK) For transmissions at 2, 5.5, and 11 Mbps

IEEE 802.11b Physical Layer Standards (continued)
Table 4-2 802.11b ISM channels
IEEE 802.11a Physical Layer Standards
  • IEEE 802.11a achieves increase in speed and
    flexibility over 802.11b primarily through OFDM
  • Use higher frequency
  • Accesses more transmission channels
  • More efficient error-correction scheme

U-NII Frequency Band
  • Total bandwidth available for IEEE 802.11a WLANs
    using U-NII is almost four times that available
    for 802.11b networks using ISM band
  • Disadvantages
  • In some countries outside U.S., 5 GHz bands
    allocated to users and technologies other than
  • Interference from other devices is growing
  • Interference from other devices one of primary
    sources of problems for 802.11b and 802.11a WLANs

IEEE 802.11g Physical Layer Standards
  • 802.11g combines best features of 802.11a and
  • Operates entirely in 2.4 GHz ISM frequency
  • Two mandatory modes and one optional mode
  • CCK mode used at 11 and 5.5 Mbps (mandatory)
  • OFDM used at 54 Mbps (mandatory)
  • PBCC-22 (Packet Binary Convolution Coding)
    Optional mode
  • Can transmit between 6 and 54 Mbps

IEEE 802.11g Physical Layer Standards (continued)
Table 4-8 IEEE 802.11g Physical layer standards
IEEE 802.11g Physical Layer Standards (continued)
  • Characteristics of 802.11g standard
  • Greater throughput than 802.11b networks
  • Covers broader area than 802.11a networks
  • Backward compatible
  • Only three channels
  • If 802.11b and 802.11g devices transmitting in
    same environment, 802.11g devices drop to 11 Mbps
  • Vendors can implement proprietary higher speed
  • Channel bonding and Dynamic turbo

CWNA Guide to Wireless LANs, Second Edition
  • Chapter Five
  • IEEE 802.11 Media Access Control and Network
    Layer Standards

IEEE Wireless LAN Configurations Basic Service
  • Basic Service Set (BSS) Group of wireless
    devices served by single AP
  • infrastructure mode
  • BSS must be assigned unique identifier
  • Service Set Identifier (SSID)
  • Serves as network name for BSS
  • Basic Service Area (BSA) Geographical area of a
  • Max BSA for a WLAN depends on many factors
  • Dynamic rate shifting As mobile devices move
    away from AP, transmission speed decreases

IEEE Wireless LAN Configurations Extended
Service Set
  • Extended Service Set (ESS) Comprised of two or
    more BSS networks connected via a common
    distribution system
  • APs can be positioned so that cells overlap to
    facilitate roaming
  • Wireless devices choose AP based on signal
  • Handoff

IEEE Wireless LAN Configurations Independent
Basic Service Set
  • Independent Basic Service Set (IBSS) Wireless
    network that does not use an AP
  • Wireless devices communicate between themselves
  • Peer-to-peer or ad hoc mode
  • BSS more flexible than IBSS in being able to
    connect to other wired or wireless networks
  • IBSS useful for quickly and easily setting up
    wireless network
  • When no connection to Internet or external
    network needed

IEEE 802.11 Media Access Control (MAC) Layer
  • Media Access Control (MAC) layer performs several
    vital functions in a WLAN
  • Discovering WLAN signal
  • Joining WLAN
  • Transmitting on WLAN
  • Remaining connected to WLAN
  • Mechanics of how functions performed center
    around frames sent and received in WLANs

Discovering the WLAN Beaconing
  • At regular intervals, AP (infrastructure network)
    or wireless device (ad hoc network) sends beacon
  • Announce presence
  • Provide info for other devices to join network
  • Beacon frame format follows standard structure of
    a management frame
  • Destination address always set to all ones

Discovering the WLAN Beaconing
  • Beacon frame body contains following fields
  • Beacon interval
  • Timestamp
  • Service Set Identifier (SSID)
  • Supported rates
  • Parameter sets
  • Capability information
  • In ad hoc networks, each wireless device assumes
    responsibility for beaconing
  • In infrastructure networks beacon interval
    normally 100 ms, but can be modified

Discovering the WLAN Scanning
  • Receiving wireless device must be looking for
    beacon frames
  • Passive scanning Wireless device simply listens
    for beacon frame
  • Typically, on each available channel for set
  • Active scanning Wireless device first sends out
    a management probe request frame on each
    available channel
  • Then waits for probe response frame from all
    available APs

Discovering the WLAN Scanning
Figure 5-8 Active scanning
Joining the WLAN Authentication
  • Unlike standard wired LANS, authentication
    performed before user connected to network
  • Authentication of the wireless device, not the
  • IEEE 802.11 authentication Process in which AP
    accepts or rejects a wireless device
  • Open system authentication Most basic, and
    default, authentication method
  • Shared key authentication Optional
    authentication method
  • Utilizes challenge text

Joining the WLAN Authentication
Figure 5-9 Open system authentication
Joining the WLAN Authentication (continued)
Figure 5-10 Shared key authentication
Joining the WLAN Authentication
  • Open system and Shared key authentication
    techniques are weak
  • Open System Only need SSID to connect
  • Shared Key Key installed manually on devices
  • Can be discovered by examining the devices
  • Digital certificates Digital documents that
    associate an individual with key value
  • Digitally signed by trusted third party
  • Cannot change any part of digital certificate
    without being detected

Joining the WLAN Association
  • Association Accepting a wireless device into a
    wireless network
  • Final step to join WLAN
  • After authentication, AP responds with
    association response frame
  • Contains acceptance or rejection notice
  • If AP accepts wireless device, reserves memory
    space in AP and establishes association ID
  • Association response frame includes association
    ID and supported data rates

Transmitting on the WLAN Distributed
Coordination Function (DCF)
  • MAC layer responsible for controlling access to
    wireless medium
  • Channel access methods Rules for cooperation
    among wireless devices
  • Contention Computers compete to use medium
  • If two devices send frames simultaneously,
    collision results and frames become
  • Must take steps to avoid collisions

Transmitting on the WLAN Distributed
Coordination Function
  • Carrier Sense Multiple Access with Collision
    Detection (CSMA/CD) Before networked device
    sends a frame, listens to see if another device
    currently transmitting
  • If traffic exists, wait otherwise send
  • Devices continue listening while sending frame
  • If collision occurs, stops and broadcasts a jam
  • CSMA/CD cannot be used on wireless networks
  • Difficult to detect collisions
  • Hidden node problem

Transmitting on the WLAN Distributed
Coordination Function
  • Distributed Coordination Function (DCF)
    Specifies modified version of CSMA/CD
  • Carrier Sense Multiple Access with Collision
    Avoidance (CSMA/CA)
  • Attempts to avoid collisions altogether
  • Time when most collisions occur is immediately
    after a station completes transmission
  • All stations must wait random amount of time
    after medium clear
  • Slot time

Transmitting on the WLAN Distributed
Coordination Function
  • CSMA/CA also reduces collisions via explicit
    frame acknowledgment
  • Acknowledgment frame (ACK) Sent by receiving
    device to sending device to confirm data frame
    arrived intact
  • If ACK not returned, transmission error assumed
  • CSMA/CA does not eliminate collisions
  • Does not solve hidden node problem

Transmitting on the WLAN Point Coordination
Function (PCF)
  • Polling Channel access method in which each
    device asked in sequence if it wants to transmit
  • Effectively prevents collisions
  • Point Coordination Function (PCF) AP serves as
    polling device or point coordinator
  • Point coordinator has to wait only through point
    coordination function IFS (PIFS) time gap
  • Shorter than DFIS time gap

Transmitting on the WLAN Point Coordination
Function (continued)
  • If point coordinator hears no traffic after PIFS
    time gap, sends out beacon frame
  • Field to indicate length of time that PCF
    (polling) will be used instead of DCF
  • Receiving stations must stop transmission for
    that amount of time
  • Point coordinator then sends frame to specific
    station, granting permission to transmit one
  • 802.11 standard allows WLAN to alternate between
    PCF (polling) and DCF (contention)

Transmitting on the WLAN Quality of Service
(QoS) and 802.11e
  • DCF does not work well for real-time,
    time-dependent traffic
  • Quality of Service (QoS) Capability to
    prioritize different types of frames
  • Wi-Fi Multimedia (WMM) Modeled after wired
    network QoS prioritization scheme
  • 802.11e draft defines superset of features
    intended to provide QoS over WLANs
  • Proposes two new mode of operation for 802.11 MAC

Transmitting on the WLAN Quality of Service and
Table 5-1 Wi-Fi Multimedia (WMM)
Transmitting on the WLAN Quality of Service and
  • 802.11e draft (continued)
  • Enhanced Distributed Channel Access (EDCA)
    Contention-based but supports different types of
  • Four access categories (AC)
  • Provides relative QoS but cannot guarantee
  • Hybrid Coordination Function Controlled Channel
    Access (HCCA) New form of PCF based upon polling
  • Serves as a centralized scheduling mechanism

Remaining Connected to the WLAN Reassociation
  • Reassociation Device drops connection with one
    AP and establish connection with another
  • Several reason why reassociation may occur
  • Roaming
  • Weakened signal
  • When device determines link to current AP is
    poor, begins scanning to find another AP
  • Can use information from previous scans

Remaining Connected to the WLAN Power Management
  • At set times AP send out beacon to all stations
  • Contains traffic indication map (TIM)
  • At same time, all sleeping stations switch into
    active listening mode
  • Power management in ad hoc mode
  • Ad hoc traffic indication message (ATIM) window
    Time at which all stations must be awake
  • Wireless device sends beacon to all other devices
  • Devices that previously attempted to send a frame
    to a sleeping device will send ATIM frame
    indicating that receiving device has data to
    receive and must remain awake

WLAN Network Layer Standards WLAN IP Addressing
  • In standard networking, IP protocol responsible
    for moving frames between computers
  • Network layer protocol
  • TCP/IP works on principle that each network host
    has unique IP address
  • Used to locate path to specific host
  • Routers use IP address to forward packets
  • Prohibits mobile users from switching to another
    network and using same IP number
  • Users who want to roam need new IP address on
    every network

WLAN Network Layer Standards Mobile IP
  • Provides mechanism within TCP/IP protocol to
    support mobile computing
  • Computers given home address,
  • Static IP number on home network
  • Home agent Forwarding mechanism that keeps track
    of where mobile computer located
  • When computer moves to foreign network, a foreign
    agent provides routing services
  • Assigns computer a care-of address
  • Computer registers care-of address with home agent

CWNA Guide to Wireless LANs, Second Edition
  • Chapter Six
  • Planning and Deploying a Wireless LAN

Planning for a Wireless Network
  • If you fail to plan, then you plan to fail
  • Some steps involved in planning wireless networks
    similar to planning wired network
  • Many steps significantly different
  • Basic planning steps
  • Assessing needs
  • Weighing benefits
  • Calculating costs

Assessing Needs The Need for Mobility
  • Two significant changes in business world over
    last 15 years
  • Workers have electronic tools to access
    information and accomplish significantly more
  • Restructuring of organizational hierarchies
  • Organizations are flatter
  • Teamwork is essential
  • Together, can result in decreased productivity
  • Hinders ability to collaborate and make timely
  • Mobile office needed

Assessing Needs The Need for Mobility (continued)
  • A solution to need for mobility is WLANs
  • Expand productivity zone of knowledge workers
  • Improve quality and productivity of meetings
  • Work can be performed in more locations at more
  • WLANs have been shown to add one to two hours a
    day of productive time per worker
  • Enabling worker to respond to customers,
    partners, and colleagues more quickly
  • WLANs too often viewed as optional add-on to
    computer networks

Assessing Needs Examining the Business Entity
  • Determine if business case exists for bringing
    wireless networking into corporate environment
  • What is the purpose or mission of the
  • Is the current mission expected to change in the
  • What is the size of the organization?
  • How much growth is anticipated in the
  • Obtaining firm conceptual grip on organization as
    a whole and its current status will reveal if an
    investment in wireless technology is wise

Assessing Needs Reviewing the Current Network
  • Question to ask when examining how organization
    uses current network
  • How does current network support the
    organizations mission?
  • What applications run on the network?
  • How many users does network support?
  • Strengths and weaknesses of the current network?
  • Anticipated growth in network technology?
  • Examining current network status reveals much of
    this information
  • Especially applications and number of users

Assessing Needs Reviewing the Current Network
  • Good time to document network in detail
  • Number of clients
  • Types of clients
  • Number of servers
  • The topology of the network
  • What media is being used
  • Performance of the network
  • Types of devices connected to the network

Assessing Needs Reviewing the Current Network
Table 6-1 Current network table
Assessing Needs Reviewing the Current Network
Figure 6-1 Network diagram
Determining Benefits Hard Benefits
  • Benefits that can be easily measured or
  • For WLANs, easily measured in decreased cost of
  • e.g., elimination of cabling costs
  • Using wireless technology for MAN or WAN can
    result in even higher savings

Determining Benefits Soft Benefits
  • Benefits that are difficult, if not impossible,
    to quantify accurately
  • Improved productivity
  • Enhanced collaboration and faster responsiveness
  • Flexible mobility
  • Adherence to standards
  • Improved employee satisfaction

Calculating Return on Investment (ROI)
  • Return on investment (ROI) Standard measure of
    profitability of a project
  • Total cost of project
  • Hardware, software, implementation costs,
    training, operations staff, maintenance staff and
    services, and connectivity fees
  • Less tangible costs
  • Workload management and customer satisfaction
  • Several models for calculating ROI

Calculating Return on Investment (continued)
  • Intel Corporations wireless LAN model
  • Implement a pilot
  • Develop a report
  • Assemble data
  • Calculate ROI

Table 6-2 Three-year WLAN costs and benefits
Calculating Return on Investment
Figure 6-2 Intels ROI model for WLANs
Designing the Wireless LAN
  • Involves determining
  • Which deployment scenario is best
  • Which IEEE wireless network standard should be
  • Type of AP management to implemented
  • Where wireless devices should be located

Determining the Deployment Scenario
  • First step in designing a WLAN is to decide on
    correct deployment scenario
  • Ad hoc Not connected to wired infrastructure
  • Useful where wireless infrastructure does not
    exist or services to remote networks not required
  • Infrastructure WLAN devices connect to wired
    corporate network via AP
  • Most corporate wireless LANs
  • Hotspot Provides wireless LAN service, for free
    or for a fee, from variety of public areas
  • Point-to-point remote wireless bridge Typically
    interconnects two LAN segments

Determining the Deployment Scenario
  • Deployment scenarios (continued)
  • Point-to-multipoint remote wireless bridge
    Connects multiple LAN segments
  • Ethernet to wireless bridge Connects single
    device that has an Ethernet port but not an
    802.11 NIC
  • Wireless gateway Provide single mechanism for
    managing and monitoring the wireless network

Selecting the IEEE Wireless Network Type
  • IEEE 802.11b, 802.11a, or 802.11g
  • Decision may depend on many factors
  • Do other devices in area use same frequency range
    as one of the network types?
  • What kind of coverage is needed?
  • What types of applications will be used?
  • If broader area of coverage needed, 802.11g
    standard should be considered first
  • Good balance of coverage area with speed

Selecting the IEEE Wireless Network Type
  • If interference is an issue, then 802.11a
    standard should be considered
  • Only consider 802.11b in areas where low
    bandwidth is acceptable or ad hoc wireless
    network will be used
  • Slow speed and susceptibility to interference

Deciding upon Access Point Management
  • If using infrastructure wireless network, must
    decide type of AP management
  • Fat access point AP serves as management point
  • Configuration must be done through via AP
  • Thin access point Lacks management functions
  • Management functions moved to Ethernet network
  • Management simplified, centralized
  • Handoff time reduced
  • Thin access points are proprietary

Deciding upon Access Point Management
  • Thin AP approach does not provide overall
    solution for managing entire network (wired and
  • Several vendors working on comprehensive network
    management solutions
  • Integrate wireless networks into same deployment,
    operations, and management as wired network
  • e.g., Ciscos Structured Wireless-Aware Network

Determining the Location of the Wireless Devices
Table 6-3 Interference by objects
Ad Hoc Mode
  • Wireless devices communicate directly without an
  • Three main considerations
  • Stations must be arranged so that they are all
    within proper distance limits
  • All stations must send and receive signals on
    same frequency
  • Hidden node problem must be avoided

Ad Hoc Mode
Figure 6-3 Ad hoc hidden node problem
Infrastructure Mode
  • Positioning APs correctly for an infrastructure
    WLAN is critical for ensuring that coverage area
    is sufficient
  • Interference by objects must be taken into
  • Signal should not extend beyond buildings
    exterior walls for security reasons
  • In an ESS infrastructure network with multiple
    APs, important that each APs channel set
  • Adjacent APs using same channel can cause
    interference and lost frames

Infrastructure Mode (continued)
Figure 6-4 Interference from using same channel
Infrastructure Mode (continued)
  • IEEE 802.11b and 802.11g networks divide
    frequency spectrum into 14 overlapping and
    staggered channels
  • Only channels 1, 6,and 11 do not overlap
  • Channel reuse Adjacent APs use nonoverlapping
    channels (1, 6, and 11)
  • IEEE 802.11a networks have eight nonoverlapping
  • Must ensure APs properly overlap
  • No gaps, but not too close together

Infrastructure Mode (continued)
Figure 6-5 Channel reuse
Infrastructure Mode (continued)
Figure 6-6 Flip flop between access points
Infrastructure Mode
  • Must consider number of users who will be
    associated with APs
  • Consider not only how many users will be
    associated with each AP but also what they will
    be doing

Deploying a Wireless Network
  • If planning/designing done correctly, deploying
    can be easiest step
  • Must consider actual placement of APs
  • Place APs exactly where they were designed to go
  • To avoid interference, better to place APs higher
  • Be careful if placing APs in plenums
  • If needed, can use PoE
  • Good idea to configure WLAN on own network segment

Providing User Support Training
  • Planning, designing, and deploying WLAN pointless
    if users dont receive required support
  • Training is vital to use of a WLAN
  • Users must know how to use new hardware and
  • Support staff must know how to manage network and
    diagnose problems
  • Increases effectiveness of new wireless network
  • Minimizes drop in productivity normally
    associated with installation of a new system

Providing User Support Training
  • Group training session often most effective
    training setting
  • Preferably done at same time users receive
    wireless-enabled laptops
  • Important to set appropriate user expectations
    for support and how they should request it

Providing User Support Support
  • Involves continuing follow-up in answering
    questions and assisting users
  • User support functions can be organized in
    variety of ways
  • Establishing informal peer-to-peer support groups
  • Creating formal user support groups
  • Maintaining a help desk
  • Assigning support to the information technology
  • Outsourcing support to a third party

Providing User Support Support
  • Establishing and staffing internal help desk is
    one of most effective means of support
  • Central point of contact for users who need
    assistance using network
  • Suggestions regarding a help desk
  • One telephone number for help desk
  • Plan for increased call volume after network
  • Problem tracking
  • Use surveys to determine user satisfaction
  • Periodically rotate network personnel into help
  • Use info from help desk to organize follow-up

Providing User Support Support
  • User feedback essential when installing new WLAN
  • Possibly more essential than technical feedback
  • May have IT personnel contact users for feedback
  • May schedule meetings with users to gather
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