Your SlideShare is downloading. ×
0
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Chapter 1: A First Look at Windows 2000 Professional
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

Chapter 1: A First Look at Windows 2000 Professional

871

Published on

0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total Views
871
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
54
Comments
0
Likes
0
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 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
    • Education—classrooms, presentations, libraries, access anywhere on campus
    • Military—Universal Handset, a 1.5 lb. device allows full motion video, cellular and satellite communications, and Internet access
    • Business—office space where traditional infrastructure does not exist, such as conference room or hotel room
  • 7. Wireless Communications in Industries
    • Entertainment—barcodes on tickets validated by handheld readers; fans accessing game statistics, watching replays, ordering concessions through notebook computers or PDAs
    • Travel—global positioning systems (GPS) providing emergency roadside assistance; airline passengers using wireless notebooks or PDAs
  • 8. Wireless Communications in Industries
    • Construction—scheduling construction phases and employee travel, completing payroll, diagnosing equipment
    • Warehouse Management—inventory, shipping, reading bar-coded pallet labels
    • Health Care—tracking 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.  
  • 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 10 th 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 1’s and 0’s 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 AP’s 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 frames—set up initial communication between client and AP, as seen in Figure 6-21
      • Control frames—provide assistance in delivering frame that contains data, as seen in Figure 6-22
      • Data frames—carry 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
    • Mobility—employees have contact with network; work in teams for better productivity
    • Easier and less expensive installation—no need to install cables or modify historical property; easy to remodel office without concern for network access
    • Increased reliability—no outages caused by cable failure
    • Disaster recovery—easy to relocate office quickly using WLANs and laptop computers
  • 94. Wireless Disadvantages
    • Health risks?—devices emit small levels of RF
      • FDA—inconclusive 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
    • Security—some wireless technologies add security such as encryption or coded numbers for authorization to gain access to the network
  • 95. Wireless Performance Gap WIDE AREA CIRCUIT SWITCHING User Bit-Rate (kbps) 14.4 digital cellular 28.8 modem ISDN ATM 9.6 modem 2.4 modem 2.4 cellular 32 kbps PCS 9.6 cellular wired- wireless bit-rate "gap" 1970 2000 1990 1980 YEAR LOCAL AREA PACKET SWITCHING User Bit-Rate (kbps) Ethernet FDDI ATM 100 M Ethernet Polling Packet Radio 1st gen WLAN 2nd gen WLAN wired- wireless bit-rate "gap" 1970 2000 1990 1980 .01 .1 1 10 100 1000 10,000 100,000 YEAR .01 .1 1 10 100 1000 10,000 100,000
  • 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

×