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Guide to Wireless Communications


to Wireless Communications Objectives Explain how the major wireless technologies are used today - WiFi Describe the applications used in wireless technology List and ... – PowerPoint PPT presentation

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Title: Guide to Wireless Communications

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

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

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

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

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

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

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

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

  • 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

Home Wireless Network
  • 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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  • Uses devices with small radio transceivers,
    called radio modules, built onto microprocessor
  • 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

Bluetooth Headset
  • The Bluetooth headset automatically establishes a
    connection with the telephone

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

  • 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

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

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

Limited Support
  • Bluetooth is caught in chicken or egg scenario
  • Because of low market penetration, Bluetooth is
    not fully supported by hardware and software
  • 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

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
  • 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

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
  • Trend today is fewer devices instead of more, and
    cell phones have integrated capabilities that
    Bluetooth lacks

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

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

WLAN Warehouse Network
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

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
  • Wireless network interface (NIC) cards
  • Access points (AP)

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

Access Point and Wireless NIC
Office WLAN
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

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
  • This will keep RF waves away from motherboard

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
  • All operating systems before Windows XP,
    including Linux, require loading software
  • Operating systems for PDAs may soon integrate
    software to recognize a wireless NIC

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

Access Point
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

Access Point as a Bridge
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

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

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

Extended Service Set (ESS)
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

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
  • Alternative may be software that tricks network
    into seeing subnets as one network

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

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

WLAN features in PHY and MAC layers
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

Wireless changes to layers
  • Physical
  • Data Link

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
  • Physical Layer Convergence Procedure (PLCP)
    performs two basic functions, as seen in Figure
  • Reformats data into frame PMD sublayer can
  • Listens to determine when data can be sent

PHY Sublayers
PLCP Sublayer
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

PLCP Frame
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

802.11b ISM Channels
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

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

Distributed Coordination Function
  • Channel access methods refer to different ways of
  • 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

  • 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

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

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

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

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

  • 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

Reassociation Process
MAC Frame Formats
  • 802.11b specifies three different MAC frame
  • 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

Management Frame
Control Frame
Data Frame
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

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

  • 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
  • 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

  • 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

  • RF WLAN sends and receives data in two different
  • 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

  • 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

  • IEEE 802.11 standard defines wireless network,
    either mobile or fixed, that transmits up to 2
  • 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)

  • 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

  • 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)

  • 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
  • Reassociation means client drops connection with
    one access point and reestablishes connection
    with another AP

  • 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

  • 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

The Wireless Landscape
  • Wireless communication is standard means of
    communication for people in many occupations and
  • 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

Wireless Technologies
The Wireless Landscape
Wireless Advantages and Disadvantages
  • Advantages
  • Mobility
  • Easier and less expensive installation
  • Increased reliability
  • Disaster recovery
  • Disadvantages
  • Health risks ?
  • Radio signal Interference
  • Security

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
  • Disaster recoveryeasy to relocate office quickly
    using WLANs and laptop computers

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
  • Securitysome wireless technologies add security
    such as encryption or coded numbers for
    authorization to gain access to the network

Wireless Performance Gap
  • 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
  • WLANs WiFi 802.11 family

  • 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
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