CWNA Guide to Wireless LANs, Second Edition

1
CWNA Guide to Wireless LANs, Second Edition

• Chapter One
• Its a Wireless World

2
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

3
A Day in the Life of a Wireless User Car

• Bluetooth wireless standard Enables short range
  wireless communication
• Used in many small devices

4
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

5
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

6
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
  adapter)
• 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

7
Bluetooth

• Low-power wireless data and voice transmission
  technology
• 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

8
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
  lines
• WiMax Signal transmitted between antennas
• Up to 75 Mbps and over up to 35 miles
• Fixed Broadband

9
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
10
Cellular Telephony

• Global Systems for Mobile (GSM) a communications
  technology
• 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
  devices

11
Cellular Telephony (continued)
Figure 1-8 Browsing the World Wide Web
12
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
  HTML

Figure 1-9 WAP communications
13
Radio Frequency Identification (RFID)

• Like an electronic barcode
• Can contain larger amounts of updatable
  information
• Information transmitted via radio waves
• Range typically about 1 foot at 5 Mbps

Figure 1-10 RFID tag
14
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
  Internet
• Can create office in space where traditional
  infrastructure does not exist

15
Wireless LAN Applications Healthcare (continued)
Figure 1-12 Video pill
16
Wireless Advantages and Disadvantages Advantages

• Mobility is Primary advantage of wireless
  technology
• 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

17
Wireless Advantages and Disadvantages Advantages

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

18
Wireless Advantages and Disadvantages
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
  security
• 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

19
CWNA Guide to Wireless LANs, Second Edition

• Chapter Two
• Wireless LAN Devices and Standards

20
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

21
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

22
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

23
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

24
Advantages and Disadvantages of Standards
Table 2-1 Advantages and disadvantages of
standards
25
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

26
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

27
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

28
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)

29
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

30
Institute of Electrical and Electronics Engineers
Table 2-2 Current IEEE 802 committees
31
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

32
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

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)

• 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

38
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

39
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

40
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

41
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

42
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

43
CWNA Guide to Wireless LANs, Second Edition

• Chapter Three
• How Wireless Works

44
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

45
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

46
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
  cycle
• When bits change from 1 to 0 bit or vice versa

47
Antenna Concepts

• Radio waves transmitted/received using antennas

Figure 3-24 Antennas are required for sending
and receiving radio signals
48
Characteristics of RF Antenna Transmissions

• Polarization Orientation of radio waves as they
  leave the antenna

Figure 3-25 Vertical polarization
49
Characteristics of RF Antenna Transmissions
(continued)

• Wave propagation Pattern of wave dispersal

Figure 3-26 Sky wave propagation
50
Characteristics of RF Antenna Transmissions
(continued)
Figure 3-27 RF Line of Sight (LOS) propagation
51
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
  direction
• 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
  links

52
CWNA Guide to Wireless LANs, Second Edition

• Chapter Four
• IEEE 802.11 Physical Layer Standards

53
Introduction
Figure 4-2 OSI data flow
54
Introduction (continued)
Table 4-1 OSI layers and functions
55
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
  stations
• Other three used in IEEE 802.11 WLANs

56
Narrowband Transmission
Figure 4-3 Narrowband transmission
57
Spread Spectrum Transmission
Figure 4-4 Spread spectrum transmission
58
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)

59
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

60
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

61
IEEE 802.11 Physical Layer Standards (continued)
Figure 4-10 Data Link sublayers
62
IEEE 802.11 Physical Layer Standards (continued)
Figure 4-11 PHY sublayers
63
IEEE 802.11b Physical Layer Standards (continued)

• PLCP frame made up of three parts
• Preamble prepares receiving device for rest of
  frame
• 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

64
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

65
IEEE 802.11b Physical Layer Standards (continued)
Table 4-2 802.11b ISM channels
66
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

67
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
  WLANs
• Interference from other devices is growing
• Interference from other devices one of primary
  sources of problems for 802.11b and 802.11a WLANs

68
IEEE 802.11g Physical Layer Standards

• 802.11g combines best features of 802.11a and
  802.11b
• 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

69
IEEE 802.11g Physical Layer Standards (continued)
Table 4-8 IEEE 802.11g Physical layer standards
70
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
  speeds
• Vendors can implement proprietary higher speed
• Channel bonding and Dynamic turbo

71
CWNA Guide to Wireless LANs, Second Edition

• Chapter Five
• IEEE 802.11 Media Access Control and Network
  Layer Standards

72
IEEE Wireless LAN Configurations Basic Service
Set

• 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
  BSS
• Max BSA for a WLAN depends on many factors
• Dynamic rate shifting As mobile devices move
  away from AP, transmission speed decreases

73
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
  strength
• Handoff

74
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

75
IEEE 802.11 Media Access Control (MAC) Layer
Standards

• 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

76
Discovering the WLAN Beaconing

• At regular intervals, AP (infrastructure network)
  or wireless device (ad hoc network) sends beacon
  frame
• 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

77
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

78
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
  period
• 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

79
Discovering the WLAN Scanning
Figure 5-8 Active scanning
80
Joining the WLAN Authentication

• Unlike standard wired LANS, authentication
  performed before user connected to network
• Authentication of the wireless device, not the
  user
• 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

81
Joining the WLAN Authentication
Figure 5-9 Open system authentication
82
Joining the WLAN Authentication (continued)
Figure 5-10 Shared key authentication
83
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

84
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

85
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
  unintelligible
• Must take steps to avoid collisions

86
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
  signal
• CSMA/CD cannot be used on wireless networks
• Difficult to detect collisions
• Hidden node problem

87
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

88
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

89
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

90
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
  (contention)
• Receiving stations must stop transmission for
  that amount of time
• Point coordinator then sends frame to specific
  station, granting permission to transmit one
  frame
• 802.11 standard allows WLAN to alternate between
  PCF (polling) and DCF (contention)

91
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
  Layer

92
Transmitting on the WLAN Quality of Service and
802.11e
Table 5-1 Wi-Fi Multimedia (WMM)
93
Transmitting on the WLAN Quality of Service and
802.11e

• 802.11e draft (continued)
• Enhanced Distributed Channel Access (EDCA)
  Contention-based but supports different types of
  traffic
• Four access categories (AC)
• Provides relative QoS but cannot guarantee
  service
• Hybrid Coordination Function Controlled Channel
  Access (HCCA) New form of PCF based upon polling
• Serves as a centralized scheduling mechanism

94
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

95
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

96
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

97
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

98
CWNA Guide to Wireless LANs, Second Edition

• Chapter Six
• Planning and Deploying a Wireless LAN

99
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

100
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
  decisions
• Mobile office needed

101
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
  times
• 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

102
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
  organization?
• Is the current mission expected to change in the
  future?
• What is the size of the organization?
• How much growth is anticipated in the
  organization?
• Obtaining firm conceptual grip on organization as
  a whole and its current status will reveal if an
  investment in wireless technology is wise

103
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

104
Assessing Needs Reviewing the Current Network
(continued)

• 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

105
Assessing Needs Reviewing the Current Network
(continued)
Table 6-1 Current network table
106
Assessing Needs Reviewing the Current Network
Figure 6-1 Network diagram
107
Determining Benefits Hard Benefits

• Benefits that can be easily measured or
  quantified
• For WLANs, easily measured in decreased cost of
  installation
• e.g., elimination of cabling costs
• Using wireless technology for MAN or WAN can
  result in even higher savings

108
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

109
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

110
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
111
Calculating Return on Investment
Figure 6-2 Intels ROI model for WLANs
112
Designing the Wireless LAN

• Involves determining
• Which deployment scenario is best
• Which IEEE wireless network standard should be
  used
• Type of AP management to implemented
• Where wireless devices should be located

113
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

114
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

115
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

116
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

117
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
  switch
• Management simplified, centralized
• Handoff time reduced
• Thin access points are proprietary

118
Deciding upon Access Point Management

• Thin AP approach does not provide overall
  solution for managing entire network (wired and
  wireless)
• 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
  (SWAN)

119
Determining the Location of the Wireless Devices
Table 6-3 Interference by objects
120
Ad Hoc Mode

• Wireless devices communicate directly without an
  AP
• 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

121
Ad Hoc Mode
Figure 6-3 Ad hoc hidden node problem
122
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
  consideration
• 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
  correctly
• Adjacent APs using same channel can cause
  interference and lost frames

123
Infrastructure Mode (continued)
Figure 6-4 Interference from using same channel
124
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
  channels
• Must ensure APs properly overlap
• No gaps, but not too close together

125
Infrastructure Mode (continued)
Figure 6-5 Channel reuse
126
Infrastructure Mode (continued)
Figure 6-6 Flip flop between access points
127
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

128
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

129
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
  software
• 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

130
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

131
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
  department
• Outsourcing support to a third party

132
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
  installed
• Problem tracking
• Use surveys to determine user satisfaction
• Periodically rotate network personnel into help
  desk
• Use info from help desk to organize follow-up
  training

133
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
  feedback