Guide to Wireless Communications

1
Guide to Wireless Communications
2
Objectives

• Explain how the major wireless technologies are
  used today - WiFi
• Describe the applications used in wireless
  technology
• List and explain the advantages of wireless
  technology
• List and explain the disadvantages of wireless
  technology

3
Wireless the hype?

• Wireless communications is the next major event
  in the history of technology
• Wireless communications will revolutionize how we
  live
• Users will be able to access digital resources no
  matter where they find themselves

4
How Wireless Technology Is Used

• Wireless refers to any device that does not use
  wires
• Wireless communications refers to the
  transmission of user data without wires

5
Wireless Applications

• Wireless applications are found anywhere
  employees need mobility, including in the
  following industries
• Education
• Military
• Business
• Entertainment
• Travel
• Construction
• Warehouse management
• Health care

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Wireless Communications in Industries

• Educationclassrooms, presentations, libraries,
  access anywhere on campus
• MilitaryUniversal Handset, a 1.5 lb. device
  allows full motion video, cellular and satellite
  communications, and Internet access
• Businessoffice space where traditional
  infrastructure does not exist, such as conference
  room or hotel room

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Wireless Communications in Industries

• Entertainmentbarcodes on tickets validated by
  handheld readers fans accessing game statistics,
  watching replays, ordering concessions through
  notebook computers or PDAs
• Travelglobal positioning systems (GPS) providing
  emergency roadside assistance airline passengers
  using wireless notebooks or PDAs

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Wireless Communications in Industries

• Constructionscheduling construction phases and
  employee travel, completing payroll, diagnosing
  equipment
• Warehouse Managementinventory, shipping, reading
  bar-coded pallet labels
• Health Caretracking dispensed medicine,
  verifying patients bar-coded armbands, accessing
  patient records

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Current Wireless Systems

• Fixed Wireless Access (last mile)
• Wide Area Wireless Data Services (WWANs)
• Cellular Systems
• Satellite Systems Paging Systems
• HomeRF (SWAP) (now dead?)
• Bluetooth
• Wireless LANs (WiFi)
• WiFi5

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SWAP

• Shared Wireless Access Protocol (SWAP) defines
  wireless computer networks
• Allows wireless data and voice communication from
  distances up to 150 feet at speeds up to 10
  million bits per second (megabits or Mbps)
• Established by HomeRF Working Group, comprised of
  over 50 different companies
• Uses wireless home networking adapter that sends
  data over radio waves throughout the home, as
  seen in Figure 1-1

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Home Wireless Network
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HomeRF

• Shared Wireless Access Protocol (SWAP), Home RF
  is an open industry specification that allows
  wireless devices to share information around home
• Operates in license-free 2.4 GHz frequency and
  uses frequency-hopping spread spectrum (FHSS)
• Provides quality-of-service (QoS) that
  prioritizes time-sensitive transmissions
• Version 1.0, introduced in 2000, transmits at
  1.6 Mbps, but version 2.0, released in 2001,
  transmits at 10 Mbps

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Bluetooth

• Uses devices with small radio transceivers,
  called radio modules, built onto microprocessor
  chips
• Special software, called a link manager,
  identifies other Bluetooth devices, creates links
  with them, and sends and receives data
• Transmits at up to 1 Mbps over a distance of 33
  feet and is not impeded by physical barriers
• Bluetooth products created by over 1500 computer,
  telephone, and peripheral vendors

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Bluetooth Headset

• The Bluetooth headset automatically establishes a
  connection with the telephone

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Piconet

• Two or more Bluetooth devices that send and
  receive data make up a personal area network
  (PAN), also called a piconet
• Figure 1-3 shows a Bluetooth network

Bluetooth was named after the 10th century Danish
King Harold Bluetooth, who was responsible for
unifying Scandinavia
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Bluetooth Network
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Network Topology

• Two types of Bluetooth network topologies
• Piconet
• Scatternet (collection of piconets)
• Two Bluetooth devices within range automatically
  connect
• One device is the master, controlling all
  wireless traffic
• The other is the slave, taking commands from the
  master.

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Piconets

• A piconet is one master and at least one slave
  using the same channel
• An active slave is sending transmissions
• A passive slave is not actually participating

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Bluetooth Issues

• Many challenges face Bluetooth
• Cost
• Limited support
• Shortcomings in protocol itself
• Positioning in marketplace
• Conflicts with other devices in radio spectrum

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Cost

• Chips have decreased in price to about 15 from a
  high of over 75
• Not advantageous to replace a 7 cable with a 15
  chip
• Many think cost must come down to about 5
  before Bluetooth reaches competitive advantage

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Limited Support

• Bluetooth is caught in chicken or egg scenario
• Because of low market penetration, Bluetooth is
  not fully supported by hardware and software
  vendors
• Users reluctant to purchase technology that is
  not fully supported
• Microsoft is straddling the fence
• Provides Bluetooth support for Pocket PC 2002
• Does not support Bluetooth in Windows XP

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Protocol Limitations

• Major limitation is no hand-off between piconets
• Unlike cell phone switching, Bluetooth connection
  is broken and must be restored with new master
  when device moves from one piconet area to
  another
• Bluetooth provides less than optimal security by
  authenticating devices instead of users
• Devices cannot determine how function of other
  devices can be used in cooperating setting

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Market Position

• Current position is between IEEE 802.11x WLANs
  and cell phones
• WLAN is preferred technology for connecting
  wireless devices to form network
• WLAN is mature, robust, flexible, popular
  technology
• Trend today is fewer devices instead of more, and
  cell phones have integrated capabilities that
  Bluetooth lacks

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Spectrum Conflict

• The 2.4 GHz band that Bluetooth uses conflicts
  with IEEE 802.11b WLANs
• WLAN may drop connection when detects another
  device sharing its frequency
• Most obvious fix is moving Bluetooth device away
  from WLAN
• Many vendors offer products that let Bluetooth
  and 802.11b WLANs share spectrum
• New 802.11a WLAN standard uses a different
  frequency, eliminating the conflict

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Wireless Local Area Network (WLAN)

• Based on the Institute of Electrical and
  Electronic Engineers (IEEE) 802.11b networking
  standard
• WLAN computers transmit up to 11 Mbps at
  distances of 375 feet
• IEEE 802.11a standard increases bandwidth to 54
  Mbps
• Figure 1-8 shows a WLAN warehouse network
• 802.11 often called wireless ethernet

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WLAN Warehouse Network
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WLAN Applications

• Almost nonexistent until 2000, WLANs have
  experienced astonishing growth, with sales
  expected to top 34 billion by 2004
• WLANs have broad range of uses including colleges
  and schools, businesses, airports, warehouses,
  shopping malls, and stadiums
• WLANs have taken the world by storm and the list
  of users grows daily

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How WLANs Operate

• Although a variety of radio frequency WLANs
  exist, different products share similarities and
  operate similarly
• Only two components are required for a wireless
  network
• Wireless network interface (NIC) cards
• Access points (AP)

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Wireless NIC and Access Point (AP)

• Each computer on WLAN uses wireless network
  interface card (NIC) with built-in antenna
• Wireless NIC sends signals through radio waves to
  a fixed access point (AP)
• AP point may be attached to a wired LAN
• Figure 1-9 shows an AP and wireless NIC
• WLANs also used in office environments, as shown
  in Figure 1-10

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Access Point and Wireless NIC
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Office WLAN
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Wireless Network Interface Card

• NIC connects computer to network so it can send
  and receive data
• On wired network, NIC has a port for a cable
  connector, as seen in Figure 6-1
• On wireless network, the NIC has an antenna to
  send and receive RF signals
• NIC changes internal data from parallel to
  serial, divides data into packets with sending
  and receiving addresses, determines when to send
  packet, and transmits packet

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Integrated Wireless NICs

• Some vendors plan integrating components of
  wireless NIC onto single chip on motherboard
• Some notebook manufacturers will integrate
  wireless NIC into top of notebook behind LCD
  display
• This will keep RF waves away from motherboard

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Software for Wireless NICs

• Software may be part of operating system itself
• Windows XP has software integrated while previous
  versions of Windows do not
• Software may be separate program loaded into the
  computer
• All operating systems before Windows XP,
  including Linux, require loading software
• Operating systems for PDAs may soon integrate
  software to recognize a wireless NIC

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Access Point

• An access point (AP) has three main parts
• An antenna and a radio transmitter/receiver
• An RJ-45 wired network interface to connect to a
  wired network
• Special bridging software

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Access Point
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Functions of an Access Point

• Access point has two basic functions
• Acts as base station for wireless network
• Acts as bridge between wireless and wired network
• Bridges are LAN connectors at MAC level
• See Figure 6-7

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Access Point as a Bridge
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Characteristics of an Access Point

• Range approximately 375 feet (115 meters)
• Generally supports over 100 users
• One access point for each 50 users with light
  email and basic Internet access
• One access point per 20 users for heavy network
  access and large file transfer
• APs typically mounted on ceiling, but AC power
  may be a problem
• Power over Ethernet feature delivers DC power
  through standard unshielded twisted pair (UTP)
  Ethernet cable

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Ad Hoc Mode

• Ad Hoc Mode or peer-to-peer mode lets wireless
  clients communicate among themselves without an
  access point
• Officially called Independent Basic Services Set
  (IBSS), this mode is easy to set up, but it does
  not have access to a wired network
• See Figure 6-8

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Ad Hoc Mode
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Infrastructure Mode

• Infrastructure Mode, also called Basic Service
  Set (BSS), has wireless clients and an access
  point
• More access points can be added to create an
  Extended Service Set (ESS)
• See Figure 6-9

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Extended Service Set (ESS)
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Features of Access Points

• Coverage area should overlap when using multiple
  access points
• Wireless clients survey radio frequencies to find
  an AP that provides better service
• A seamless handoff occurs when client associates
  with new AP

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ESS and Subdivided Networks

• Drawback of ESS WLANs is that all wireless
  clients and APs must be part of same network to
  allow roaming
• Network managers like to subdivide networks into
  subnets, but this prevents clients from roaming
  freely
• Alternative may be software that tricks network
  into seeing subnets as one network

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Wireless Gateway

• Devices that follow 802.11 standard are becoming
  less expensive and more popular
• Wireless Gateway has made future of HomeRF very
  shaky
• Wireless gateway has wireless access point,
  Network Address Translator (NAT) router,
  firewall, connections for DSL and cable modems,
  and other features

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IEEE 802.11

• Introduced in 1990
• Defines cable-free local area network with either
  fixed or mobile locations that transmit at either
  1 or 2 Mbps
• Uses OSI model with functions of PHY and MAC
  layer performing WLAN features
• See Figure 6-10
• Slow bandwidth insufficient for most network
  applications

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WLAN features in PHY and MAC layers
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IEEE 802.11b

• 1999 amendment to 802.11 standard
• Added two higher speeds 5.5 and 11 Mbps
• Called Wi-Fi
• Quickly became standard for WLANs

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Wireless changes to layers

• Physical
• Data Link

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Physical Layer

• Physical layer that sends and receives signals
  from network is divided into two parts
• See Figure 6-11
• Physical Medium Dependent (PMD) sublayer defines
  how data is transmitted and received through the
  medium
• Physical Layer Convergence Procedure (PLCP)
  performs two basic functions, as seen in Figure
  6-12
• Reformats data into frame PMD sublayer can
  transmit
• Listens to determine when data can be sent

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PHY Sublayers
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PLCP Sublayer
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Physical Layer Convergence Procedure Standards

• Based on direct sequence spread spectrum (DSSS)
• Reformats data from MAC layer into frame that PMD
  sublayer can transmit
• See Figure 6-13
• Frame has three parts
• Preamble and Header transmit at 1 Mbps
• Data portion, containing from 1 to 16,384 bits,
  may be sent at faster rate

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PLCP Frame
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Physical Medium Dependent Standards

• Frame created by PLCP passes to PMD sublayer
  where binary 1s and 0s are translated into
  radio signals for transmission
• 802.11b standard uses Industrial, Scientific, and
  Medical (ISM) band for transmissions
• May use 14 frequencies, beginning at 2.412 GHz
  and incrementing in .005 GHz steps
• See Table 6-1

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802.11b ISM Channels
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Medium Access Control Layer Changes

• 802.11 Data Link layer has two sublayers
• Logical Link Control (LLC), used in 802.11b
  wireless networks with no change from wired
  network functions
• Media Access control (MAC) contains all changes
  necessary for 802.11b WLANs

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Two Kinds of Coordination

• Coordination necessary among devices sharing same
  RF spectrum
• Two kinds of coordination
• Distributed coordination function is 802.11b
  standard
• Point coordination function is optional

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Distributed Coordination Function

• Channel access methods refer to different ways of
  sharing
• Contention
• Computers compete for use of network
• May cause collisions that result in scrambled
  messages, as seen in Figure 6-14
• Must first listen to be sure no other device is
  transmitting

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Collision
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CSMA/CD

• 802.3 Ethernet standard uses contention with
  listening as channel access method
• Carrier Sense Multiple Access with Collision
  Detection (CSMA/CD)
• After a collision, each computer waits a random
  amount of time, called backoff interval, before
  attempting to resend
• See Figure 6-15

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CSMA/CD
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Distributed Coordination Function (DCF)

• 802.11b wireless networks cannot use CSMA/CD
  because radio signals drown out ability to detect
  collisions
• 802.11b uses Distributed Coordination Function
  (DCF) with modified procedure known as Carrier
  Sense Multiple Access with Collision Avoidance
  (CSMA/CA)
• Following collision, clients wait random amount
  of slot time after medium is clear
• This technique helps reduce collisions

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Packet Acknowledgement (ACK)

• CSMA/CA also reduces collisions by using explicit
  packet acknowledgement (ACK)
• Receiving client must send back to sending client
  an acknowledgement packet showing that packet
  arrived intact
• If ACK frame is not received by sending client,
  data packet is transmitted again after random
  waiting time
• Figure 6-16 illustrates CSMA/CA

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CSMA/CA
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Point Coordination Function

• Polling, an orderly channel access method,
  prevents collisions by requiring device to get
  permission before transmitting
• Each computer is asked in sequence if it wants
  to transmit, as shown in Figure 6-18
• 802.11b uses an optional polling function known
  as Point Coordination Function (PCF)
• Beacon frame indicates how long PCF will be used
• If client has nothing to transmit, it returns a
  null data frame

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Polling
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Association and Reassociation

• MAC layer uses association and reassociation to
  make sure client joins WLAN and stays connected
• Uses either active or passive scanning process
• Passive scanning has client listen for signal
  containing APs Service Set Identifier (SSID
• Active scanning has client send out probe frame
  and wait for probe response frame from AP
• After locating AP, client sends associate request
  frame and may join network after receiving frame
  with status code and client ID number

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Reassociation

• Reassociation involves dropping connection with
  one access point and establishing connection with
  another AP
• Allows mobile clients to roam beyond coverage
  area of single AP
• Allows client to find new AP if original one
  becomes weak or has interference
• Client scans to find new AP and sends
  reassociation request frame
• New AP then sends disassociation frame to old AP
  as shown in Figure 6-19

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Reassociation Process
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MAC Frame Formats

• 802.11b specifies three different MAC frame
  formats
• Management framesset up initial communication
  between client and AP, as seen in Figure 6-21
• Control framesprovide assistance in delivering
  frame that contains data, as seen in Figure 6-22
• Data framescarry information to be transmitted
  to destination client, as seen in Figure 6-23

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Management Frame
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Control Frame
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Data Frame
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High Speed WLANs

• Three standards for high-speed WLANs that
  transmit at speeds over 15 Mbps
• IEEE 802.11a
• IEEE 802.11g
• HiperLAN/2
• All WLANs are concerned with security
• How to prevent unauthorized access

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IEEE 802.11a

• Approved in 1999, 802.11a transmits at speeds of
  5.5 Mbps and 11 Mbps
• Great demand for 802.11a WLANS, also called
  Wi-Fi5, with maximum speed of 54 Mbps
• Devices use gallium arsenide (GaAs) or silicon
  germanium (SiGe) rather than CMOS semiconductors
• Increased speed achieved by higher frequency,
  more transmission channels, multiplexing
  techniques, and more efficient error-correction

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Summary

• Radio Frequency (RF) wireless local area networks
  (WLANs) have wide range of uses
• Wireless NIC performs same functions as wired
  NIC, but it uses antenna to send and receive
  signals
• Wireless NIC may be PCI (Peripheral Component
  Interface) expansion card for desktop PC, Type II
  PC Card for notebook computer, or Compact Flash
  (CF) Card for smaller device like PDA

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Summary

• Access point (AP) contains three major parts
• Antenna
• Radio transmitter/receiver
• RJ-45 interface to connect by cable to standard
  wired network by using special bridging software
• AP has two basic functions
• Acts as base station for wireless network
• Acts as bridge between wireless and wired networks

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Summary

• RF WLAN sends and receives data in two different
  modes
• Ad hoc mode lets wireless clients communicate
  among themselves without an access point
• Basic Service Set (BSS) infrastructure mode
  consists of wireless clients and at least one
  access point
• Can add more access points to increase coverage
  area and create Extended Basic Service Set (ESS),
  consisting of two or more BSS wireless networks

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Summary

• HomeRF, also known as Shared Wireless Access
  Protocol (SWAP) defines how wireless devices such
  as computers and cordless phones can share and
  communicate around the home
• Home RF version 1.0 products, introduced in 2000,
  transmit at 1.6 Mbps
• Version 2.0, released in 2001, transmits at 10
  Mbps

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Summary

• IEEE 802.11 standard defines wireless network,
  either mobile or fixed, that transmits up to 2
  Mbps
• Much too slow for most network applications
• IEEE 802.11b standard quickly became standard for
  wireless networks when it added two higher
  speeds 5.5 Mbps and 11 Mbps
• Physical Layer Convergence Procedure Standard
  (PLCP) for 802.11b uses direct sequence spread
  spectrum (DSSS)

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Summary

• The PLCP reformats data from MAC layer into frame
  that PMD sublayer can transmit.
• Frame has three parts preamble, header, and data
• 802.11b uses Industrial, Scientific, and Medical
  (ISM) band for transmission at 11, 5.5, 2, or 1
  Mbps

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Summary

• 802.11b uses Distributed Coordination Function
  (DCF) access method that specifies a modified
  Carrier Sense Multiple Access with Collision
  Avoidance (CSMA/CA) procedure
• CDMA/CA makes all clients wait random amount of
  time following collision
• Reduces collisions by using explicit packet
  acknowledgements (ACK)

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Summary

• MAC layer of 802.11b standard uses association
  and reassociation to allow client to join WLAN
  and stay connected
• Association uses either passive or active
  scanning to determines whether wireless client or
  access point should be accepted as part of
  network
• Reassociation means client drops connection with
  one access point and reestablishes connection
  with another AP

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Summary

• 802.11b defines power management to conserve
  battery power without missing data transmissions
• 802.11b specifies three different types of MAC
  frame formats
• Management frames set up communications between
  client and access point
• Control frames assist in delivering data frames
• Data frames carry information being transmitted

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Summary

• 802.11 standard defines three different
  interframe spaces (PFS) or time gaps
• Rather than being dead space, these standard
  spacing intervals or time gaps between
  transmission of data frames are used for special
  types of transmissions

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The Wireless Landscape

• Wireless communication is standard means of
  communication for people in many occupations and
  circumstances
• Table 1-1 summarizes wireless technologies,
  transmission distance, and speed
• Figure 1-14 shows a wireless landscape
• Job market to support wireless technology is
  already exploding

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Wireless Technologies
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The Wireless Landscape
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Wireless Advantages and Disadvantages

• Advantages
• Mobility
• Easier and less expensive installation
• Increased reliability
• Disaster recovery

• Disadvantages
• Health risks ?
• Radio signal Interference
• Security

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Wireless Advantages

• Mobilityemployees have contact with network
  work in teams for better productivity
• Easier and less expensive installationno need to
  install cables or modify historical property
  easy to remodel office without concern for
  network access
• Increased reliabilityno outages caused by cable
  failure
• Disaster recoveryeasy to relocate office quickly
  using WLANs and laptop computers

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Wireless Disadvantages

• Health risks?devices emit small levels of RF
• FDAinconclusive about safety of wireless devices
  
• FCC, FDA, and EPA set exposure guidelines for
  wireless phones in 1996 Specific Absorption Rate
  (SAR) of no more than 1.6 watts per kilogram
• Radio signal interference--other devices
  interfere
• Securitysome wireless technologies add security
  such as encryption or coded numbers for
  authorization to gain access to the network

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Wireless Performance Gap
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Summary

• Wireless communications, including Internet
  connections and networks, are becoming standard
  in business world
• SWAP connects different devices for home users
• Quickly becoming obselete
• Bluetooth connects some devices over short
  distances
• WLANs WiFi 802.11 family

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Summary

• WLANS are fixture of business networks
• WLAN applications found in wide variety of
  industries and organizations
• Primary advantage of WLAN is mobility or freedom
  to move without being connected by a cable
• Other advantages include easier and less
  expensive installation, increased network
  reliability, and support for disaster recovery