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Guide to Wireless Communications

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Title: 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

6
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

7
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

8
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

9
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

10
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

11
Home Wireless Network
12
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

13
(No Transcript)
14
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

15
Bluetooth Headset
  • The Bluetooth headset automatically establishes a
    connection with the telephone

16
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
17
Bluetooth Network
18
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.

19
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

20
Bluetooth Issues
  • Many challenges face Bluetooth
  • Cost
  • Limited support
  • Shortcomings in protocol itself
  • Positioning in marketplace
  • Conflicts with other devices in radio spectrum

21
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

22
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

23
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

24
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

25
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

26
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

27
WLAN Warehouse Network
28
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

29
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)

30
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

31
Access Point and Wireless NIC
32
Office WLAN
33
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

34
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

35
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

36
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

37
Access Point
38
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

39
Access Point as a Bridge
40
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

41
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

42
Ad Hoc Mode
43
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

44
Extended Service Set (ESS)
45
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

46
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

47
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

48
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

49
WLAN features in PHY and MAC layers
50
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

51
Wireless changes to layers
  • Physical
  • Data Link

52
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

53
PHY Sublayers
54
PLCP Sublayer
55
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

56
PLCP Frame
57
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

58
802.11b ISM Channels
59
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

60
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

61
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

62
Collision
63
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

64
CSMA/CD
65
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

66
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

67
CSMA/CA
68
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

69
Polling
70
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

71
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

72
Reassociation Process
73
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

74
Management Frame
75
Control Frame
76
Data Frame
77
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

78
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

79
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

80
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

81
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

82
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

83
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)

84
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

85
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)

86
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

87
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

88
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

89
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

90
Wireless Technologies
91
The Wireless Landscape
92
Wireless Advantages and Disadvantages
  • Advantages
  • Mobility
  • Easier and less expensive installation
  • Increased reliability
  • Disaster recovery
  • Disadvantages
  • Health risks ?
  • Radio signal Interference
  • Security

93
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

94
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

95
Wireless Performance Gap
96
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

97
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
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