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Guide  to  Wireless Communications
Objectives <ul><li>Explain how the major wireless technologies are used today - WiFi </li></ul><ul><li>Describe the applic...
Wireless – the hype? <ul><li>Wireless communications is the next major event in the history of technology </li></ul><ul><l...
How Wireless Technology  Is Used <ul><li>Wireless refers to any device that does not use wires </li></ul><ul><li>Wireless ...
Wireless Applications <ul><li>Wireless applications are found anywhere employees need mobility, including in the  followin...
Wireless Communications in Industries <ul><li>Education—classrooms, presentations, libraries, access anywhere on campus </...
Wireless Communications in Industries <ul><li>Entertainment—barcodes on tickets validated by handheld readers; fans access...
Wireless Communications in Industries <ul><li>Construction—scheduling construction phases and employee travel, completing ...
Current Wireless Systems <ul><li>Fixed Wireless Access (last mile) </li></ul><ul><li>Wide Area Wireless Data Services (WWA...
SWAP <ul><li>Shared Wireless Access Protocol (SWAP) defines wireless computer networks  </li></ul><ul><ul><li>Allows wirel...
Home Wireless Network
HomeRF <ul><li>Shared Wireless Access Protocol (SWAP), Home RF is an open industry specification that allows wireless devi...
 
Bluetooth <ul><li>Uses devices with small radio transceivers, called radio modules, built onto microprocessor chips </li><...
Bluetooth Headset <ul><li>The Bluetooth headset automatically establishes a connection  with the telephone </li></ul>
Piconet <ul><li>Two or more Bluetooth devices that send and receive data make up a personal area network (PAN), also calle...
Bluetooth Network
Network Topology <ul><li>Two types of Bluetooth network topologies  </li></ul><ul><ul><li>Piconet </li></ul></ul><ul><ul><...
Piconets <ul><li>A piconet is one master and at least one slave using the same channel </li></ul><ul><li>An active slave i...
Bluetooth Issues <ul><li>Many challenges face Bluetooth </li></ul><ul><ul><li>Cost </li></ul></ul><ul><ul><li>Limited supp...
Cost <ul><li>Chips have decreased in price to about $15 from a high of over $75 </li></ul><ul><ul><li>Not advantageous to ...
Limited Support <ul><li>Bluetooth is caught in “chicken or egg” scenario </li></ul><ul><ul><li>Because of low market penet...
Protocol Limitations <ul><li>Major limitation is no hand-off between piconets </li></ul><ul><ul><li>Unlike cell phone swit...
Market Position <ul><li>Current position is between IEEE 802.11x WLANs and cell phones </li></ul><ul><ul><li>WLAN is prefe...
Spectrum Conflict <ul><li>The 2.4 GHz band that Bluetooth uses conflicts with IEEE 802.11b WLANs </li></ul><ul><ul><li>WLA...
Wireless Local Area Network (WLAN) <ul><li>Based on the Institute of Electrical and Electronic Engineers (IEEE) 802.11b ne...
WLAN Warehouse Network
WLAN Applications <ul><li>Almost nonexistent until 2000, WLANs have experienced astonishing growth, with sales expected to...
How WLANs Operate <ul><li>Although a variety of radio frequency WLANs exist, different products share  similarities and op...
Wireless NIC and  Access Point (AP) <ul><li>Each computer on WLAN uses wireless network interface card (NIC) with built-in...
Access Point and Wireless NIC
Office WLAN
Wireless Network  Interface Card <ul><li>NIC connects computer to network so it can send and receive data </li></ul><ul><l...
Integrated Wireless NICs <ul><li>Some vendors plan integrating components of wireless NIC onto single chip on motherboard ...
Software for Wireless NICs <ul><li>Software may be part of operating system itself </li></ul><ul><ul><li>Windows XP has so...
Access Point <ul><li>An access point (AP) has three main parts </li></ul><ul><ul><li>An antenna and a radio transmitter/re...
Access Point
Functions of an  Access Point <ul><li>Access point has two basic functions </li></ul><ul><ul><li>Acts as base station for ...
Access Point as a Bridge
Characteristics of an Access Point <ul><li>Range approximately 375 feet (115 meters) </li></ul><ul><li>Generally supports ...
Ad Hoc Mode  <ul><li>Ad Hoc Mode or peer-to-peer mode lets wireless clients communicate among themselves without an access...
Ad Hoc Mode
Infrastructure Mode <ul><li>Infrastructure Mode, also called Basic Service Set (BSS), has wireless clients and an access p...
Extended Service Set (ESS)
Features of Access Points <ul><li>Coverage area should overlap when using multiple access points </li></ul><ul><ul><li>Wir...
ESS and Subdivided Networks <ul><li>Drawback of ESS WLANs is that all wireless clients and APs must be part of same networ...
Wireless Gateway <ul><li>Devices that follow 802.11 standard are becoming less expensive and more popular </li></ul><ul><l...
IEEE 802.11 <ul><li>Introduced in 1990 </li></ul><ul><li>Defines cable-free local area network with either fixed or mobile...
WLAN features in PHY and MAC layers
IEEE 802.11b <ul><li>1999 amendment to 802.11 standard </li></ul><ul><li>Added two higher speeds: 5.5 and 11 Mbps </li></u...
Wireless changes to layers <ul><li>Physical </li></ul><ul><li>Data Link </li></ul>
Physical Layer <ul><li>Physical layer that sends and receives signals  from network is divided into two parts </li></ul><u...
PHY Sublayers
PLCP Sublayer
Physical Layer Convergence Procedure Standards <ul><li>Based on direct sequence spread spectrum (DSSS) </li></ul><ul><li>R...
PLCP Frame
Physical Medium Dependent Standards <ul><li>Frame created by PLCP passes to PMD sublayer where binary 1’s and 0’s are tran...
802.11b ISM Channels
Medium Access Control Layer Changes <ul><li>802.11 Data Link layer has two sublayers </li></ul><ul><ul><li>Logical Link Co...
Two Kinds of Coordination <ul><li>Coordination necessary among devices sharing same RF spectrum </li></ul><ul><li>Two kind...
Distributed Coordination Function <ul><li>Channel access methods refer to different ways of sharing  </li></ul><ul><li>Con...
Collision
CSMA/CD <ul><li>802.3 Ethernet standard uses contention with “listening” as channel access method </li></ul><ul><ul><li>Ca...
CSMA/CD
Distributed Coordination Function (DCF) <ul><li>802.11b wireless networks cannot use CSMA/CD because radio signals drown o...
Packet Acknowledgement (ACK) <ul><li>CSMA/CA also reduces collisions by using explicit packet acknowledgement (ACK) </li><...
CSMA/CA
Point Coordination Function <ul><li>Polling, an orderly channel access method, prevents collisions by requiring device to ...
Polling
Association and Reassociation <ul><li>MAC layer uses association and reassociation to make sure client joins WLAN and stay...
Reassociation <ul><li>Reassociation involves dropping connection with one access point and establishing connection with an...
Reassociation Process
MAC Frame Formats <ul><li>802.11b specifies three different MAC frame formats  </li></ul><ul><ul><li>Management frames—set...
Management Frame
Control Frame
Data Frame
High Speed WLANs <ul><li>Three standards for high-speed WLANs that transmit at speeds over 15 Mbps </li></ul><ul><ul><li>I...
IEEE 802.11a <ul><li>Approved in 1999, 802.11a transmits at speeds of 5.5 Mbps and 11 Mbps </li></ul><ul><li>Great demand ...
Summary <ul><li>Radio Frequency (RF) wireless local area networks (WLANs) have wide range of uses </li></ul><ul><li>Wirele...
Summary <ul><li>Access point (AP) contains three major parts </li></ul><ul><ul><li>Antenna </li></ul></ul><ul><ul><li>Radi...
Summary <ul><li>RF WLAN sends and receives data in two different modes </li></ul><ul><ul><li>Ad hoc mode lets wireless cli...
Summary <ul><li>HomeRF, also known as Shared Wireless Access Protocol (SWAP) defines how wireless devices such as computer...
Summary <ul><li>IEEE 802.11 standard defines wireless network, either mobile or fixed, that transmits up to 2 Mbps </li></...
Summary <ul><li>The PLCP reformats data from MAC layer into frame that PMD sublayer can transmit. </li></ul><ul><li>Frame ...
Summary <ul><li>802.11b uses Distributed Coordination Function (DCF) access method that specifies a modified Carrier Sense...
Summary <ul><li>MAC layer of 802.11b standard uses association and reassociation to allow client to join WLAN and stay con...
Summary <ul><li>802.11b defines power management to conserve battery power without missing data transmissions </li></ul><u...
Summary <ul><li>802.11 standard defines three different interframe spaces (PFS) or time gaps </li></ul><ul><ul><li>Rather ...
The Wireless Landscape <ul><li>Wireless communication is standard means of communication for people in many occupations an...
Wireless Technologies
The Wireless Landscape
Wireless Advantages and Disadvantages <ul><li>Advantages </li></ul><ul><ul><li>Mobility </li></ul></ul><ul><ul><li>Easier ...
Wireless Advantages <ul><li>Mobility—employees have contact with network; work in teams for better productivity </li></ul>...
Wireless Disadvantages <ul><li>Health risks?—devices emit small levels of RF </li></ul><ul><ul><li>FDA—inconclusive about ...
Wireless Performance Gap WIDE AREA CIRCUIT SWITCHING User  Bit-Rate  (kbps) 14.4 digital cellular 28.8 modem ISDN ATM 9.6 ...
Summary <ul><li>Wireless communications, including Internet connections and networks, are becoming standard  in business w...
Summary <ul><li>WLANS are fixture of business networks </li></ul><ul><li>WLAN applications found in wide variety  of indus...
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Chapter 1: A First Look at Windows 2000 Professional

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Transcript of "Chapter 1: A First Look at Windows 2000 Professional"

  1. 1. Guide to Wireless Communications
  2. 2. Objectives <ul><li>Explain how the major wireless technologies are used today - WiFi </li></ul><ul><li>Describe the applications used in wireless technology </li></ul><ul><li>List and explain the advantages of wireless technology </li></ul><ul><li>List and explain the disadvantages of wireless technology </li></ul>
  3. 3. Wireless – the hype? <ul><li>Wireless communications is the next major event in the history of technology </li></ul><ul><li>Wireless communications will revolutionize how we live </li></ul><ul><li>Users will be able to access digital resources no matter where they find themselves </li></ul>
  4. 4. How Wireless Technology Is Used <ul><li>Wireless refers to any device that does not use wires </li></ul><ul><li>Wireless communications refers to the transmission of user data without wires </li></ul>
  5. 5. Wireless Applications <ul><li>Wireless applications are found anywhere employees need mobility, including in the following industries : </li></ul><ul><ul><li>Education </li></ul></ul><ul><ul><li>Military </li></ul></ul><ul><ul><li>Business </li></ul></ul><ul><ul><li>Entertainment </li></ul></ul><ul><ul><li>Travel </li></ul></ul><ul><ul><li>Construction </li></ul></ul><ul><ul><li>Warehouse management </li></ul></ul><ul><ul><li>Health care </li></ul></ul>
  6. 6. Wireless Communications in Industries <ul><li>Education—classrooms, presentations, libraries, access anywhere on campus </li></ul><ul><li>Military—Universal Handset, a 1.5 lb. device allows full motion video, cellular and satellite communications, and Internet access </li></ul><ul><li>Business—office space where traditional infrastructure does not exist, such as conference room or hotel room </li></ul>
  7. 7. Wireless Communications in Industries <ul><li>Entertainment—barcodes on tickets validated by handheld readers; fans accessing game statistics, watching replays, ordering concessions through notebook computers or PDAs </li></ul><ul><li>Travel—global positioning systems (GPS) providing emergency roadside assistance; airline passengers using wireless notebooks or PDAs </li></ul>
  8. 8. Wireless Communications in Industries <ul><li>Construction—scheduling construction phases and employee travel, completing payroll, diagnosing equipment </li></ul><ul><li>Warehouse Management—inventory, shipping, reading bar-coded pallet labels </li></ul><ul><li>Health Care—tracking dispensed medicine, verifying patients’ bar-coded armbands, accessing patient records </li></ul>
  9. 9. Current Wireless Systems <ul><li>Fixed Wireless Access (last mile) </li></ul><ul><li>Wide Area Wireless Data Services (WWANs) </li></ul><ul><li>Cellular Systems </li></ul><ul><li>Satellite Systems & Paging Systems </li></ul><ul><li>HomeRF (SWAP) (now dead?) </li></ul><ul><li>Bluetooth </li></ul><ul><li>Wireless LANs (WiFi) </li></ul><ul><li>WiFi5 </li></ul>
  10. 10. SWAP <ul><li>Shared Wireless Access Protocol (SWAP) defines wireless computer networks </li></ul><ul><ul><li>Allows wireless data and voice communication from distances up to 150 feet at speeds up to 10 million bits per second (megabits or Mbps) </li></ul></ul><ul><ul><li>Established by HomeRF Working Group, comprised of over 50 different companies </li></ul></ul><ul><ul><li>Uses wireless home networking adapter that sends data over radio waves throughout the home, as seen in Figure 1-1 </li></ul></ul>
  11. 11. Home Wireless Network
  12. 12. HomeRF <ul><li>Shared Wireless Access Protocol (SWAP), Home RF is an open industry specification that allows wireless devices to share information around home </li></ul><ul><ul><li>Operates in license-free 2.4 GHz frequency and uses frequency-hopping spread spectrum (FHSS) </li></ul></ul><ul><ul><li>Provides quality-of-service (QoS) that prioritizes time-sensitive transmissions </li></ul></ul><ul><ul><li>Version 1.0, introduced in 2000, transmits at 1.6 Mbps, but version 2.0, released in 2001, transmits at 10 Mbps </li></ul></ul>
  13. 14. Bluetooth <ul><li>Uses devices with small radio transceivers, called radio modules, built onto microprocessor chips </li></ul><ul><li>Special software, called a link manager, identifies other Bluetooth devices, creates links with them, and sends and receives data </li></ul><ul><li>Transmits at up to 1 Mbps over a distance of 33 feet and is not impeded by physical barriers </li></ul><ul><li>Bluetooth products created by over 1500 computer, telephone, and peripheral vendors </li></ul>
  14. 15. Bluetooth Headset <ul><li>The Bluetooth headset automatically establishes a connection with the telephone </li></ul>
  15. 16. Piconet <ul><li>Two or more Bluetooth devices that send and receive data make up a personal area network (PAN), also called a piconet </li></ul><ul><li>Figure 1-3 shows a Bluetooth network </li></ul>Bluetooth was named after the 10 th century Danish King Harold Bluetooth, who was responsible for unifying Scandinavia
  16. 17. Bluetooth Network
  17. 18. Network Topology <ul><li>Two types of Bluetooth network topologies </li></ul><ul><ul><li>Piconet </li></ul></ul><ul><ul><li>Scatternet (collection of piconets) </li></ul></ul><ul><li>Two Bluetooth devices within range automatically connect </li></ul><ul><ul><li>One device is the master, controlling all wireless traffic </li></ul></ul><ul><ul><li>The other is the slave, taking commands from the master. </li></ul></ul>
  18. 19. Piconets <ul><li>A piconet is one master and at least one slave using the same channel </li></ul><ul><li>An active slave is sending transmissions </li></ul><ul><li>A passive slave is not actually participating </li></ul>
  19. 20. Bluetooth Issues <ul><li>Many challenges face Bluetooth </li></ul><ul><ul><li>Cost </li></ul></ul><ul><ul><li>Limited support </li></ul></ul><ul><ul><li>Shortcomings in protocol itself </li></ul></ul><ul><ul><li>Positioning in marketplace </li></ul></ul><ul><ul><li>Conflicts with other devices in radio spectrum </li></ul></ul>
  20. 21. Cost <ul><li>Chips have decreased in price to about $15 from a high of over $75 </li></ul><ul><ul><li>Not advantageous to replace a $7 cable with a $15 chip </li></ul></ul><ul><ul><li>Many think cost must come down to about $5 before Bluetooth reaches competitive advantage </li></ul></ul>
  21. 22. Limited Support <ul><li>Bluetooth is caught in “chicken or egg” scenario </li></ul><ul><ul><li>Because of low market penetration, Bluetooth is not fully supported by hardware and software vendors </li></ul></ul><ul><ul><li>Users reluctant to purchase technology that is not fully supported </li></ul></ul><ul><li>Microsoft is “straddling the fence” </li></ul><ul><ul><li>Provides Bluetooth support for Pocket PC 2002 </li></ul></ul><ul><ul><li>Does not support Bluetooth in Windows XP </li></ul></ul>
  22. 23. Protocol Limitations <ul><li>Major limitation is no hand-off between piconets </li></ul><ul><ul><li>Unlike cell phone switching, Bluetooth connection is broken and must be restored with new master when device moves from one piconet area to another </li></ul></ul><ul><li>Bluetooth provides less than optimal security by authenticating devices instead of users </li></ul><ul><li>Devices cannot determine how function of other devices can be used in cooperating setting </li></ul>
  23. 24. Market Position <ul><li>Current position is between IEEE 802.11x WLANs and cell phones </li></ul><ul><ul><li>WLAN is preferred technology for connecting wireless devices to form network </li></ul></ul><ul><ul><li>WLAN is mature, robust, flexible, popular technology </li></ul></ul><ul><ul><li>Trend today is fewer devices instead of more, and cell phones have integrated capabilities that Bluetooth lacks </li></ul></ul>
  24. 25. Spectrum Conflict <ul><li>The 2.4 GHz band that Bluetooth uses conflicts with IEEE 802.11b WLANs </li></ul><ul><ul><li>WLAN may drop connection when detects another device sharing its frequency </li></ul></ul><ul><ul><li>Most obvious fix is moving Bluetooth device away from WLAN </li></ul></ul><ul><ul><li>Many vendors offer products that let Bluetooth and 802.11b WLANs share spectrum </li></ul></ul><ul><ul><li>New 802.11a WLAN standard uses a different frequency, eliminating the conflict </li></ul></ul>
  25. 26. Wireless Local Area Network (WLAN) <ul><li>Based on the Institute of Electrical and Electronic Engineers (IEEE) 802.11b networking standard </li></ul><ul><li>WLAN computers transmit up to 11 Mbps at distances of 375 feet </li></ul><ul><li>IEEE 802.11a standard increases bandwidth to 54 Mbps </li></ul><ul><li>Figure 1-8 shows a WLAN warehouse network </li></ul><ul><li>802.11 often called wireless ethernet </li></ul>
  26. 27. WLAN Warehouse Network
  27. 28. WLAN Applications <ul><li>Almost nonexistent until 2000, WLANs have experienced astonishing growth, with sales expected to top $34 billion by 2004 </li></ul><ul><li>WLANs have broad range of uses including colleges and schools, businesses, airports, warehouses, shopping malls, and stadiums </li></ul><ul><li>WLANs have taken the world by storm and the list of users grows daily </li></ul>
  28. 29. How WLANs Operate <ul><li>Although a variety of radio frequency WLANs exist, different products share similarities and operate similarly </li></ul><ul><li>Only two components are required for a wireless network </li></ul><ul><ul><li>Wireless network interface (NIC) cards </li></ul></ul><ul><ul><li>Access points (AP) </li></ul></ul>
  29. 30. Wireless NIC and Access Point (AP) <ul><li>Each computer on WLAN uses wireless network interface card (NIC) with built-in antenna </li></ul><ul><li>Wireless NIC sends signals through radio waves to a fixed access point (AP) </li></ul><ul><ul><li>AP point may be attached to a wired LAN </li></ul></ul><ul><ul><li>Figure 1-9 shows an AP and wireless NIC </li></ul></ul><ul><li>WLANs also used in office environments, as shown in Figure 1-10 </li></ul>
  30. 31. Access Point and Wireless NIC
  31. 32. Office WLAN
  32. 33. Wireless Network Interface Card <ul><li>NIC connects computer to network so it can send and receive data </li></ul><ul><li>On wired network, NIC has a port for a cable connector, as seen in Figure 6-1 </li></ul><ul><li>On wireless network, the NIC has an antenna to send and receive RF signals </li></ul><ul><ul><li>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 </li></ul></ul>
  33. 34. Integrated Wireless NICs <ul><li>Some vendors plan integrating components of wireless NIC onto single chip on motherboard </li></ul><ul><li>Some notebook manufacturers will integrate wireless NIC into top of notebook behind LCD display </li></ul><ul><ul><li>This will keep RF waves away from motherboard </li></ul></ul>
  34. 35. Software for Wireless NICs <ul><li>Software may be part of operating system itself </li></ul><ul><ul><li>Windows XP has software integrated while previous versions of Windows do not </li></ul></ul><ul><li>Software may be separate program loaded into the computer </li></ul><ul><ul><li>All operating systems before Windows XP, including Linux, require loading software </li></ul></ul><ul><ul><li>Operating systems for PDAs may soon integrate software to recognize a wireless NIC </li></ul></ul>
  35. 36. Access Point <ul><li>An access point (AP) has three main parts </li></ul><ul><ul><li>An antenna and a radio transmitter/receiver </li></ul></ul><ul><ul><li>An RJ-45 wired network interface to connect to a wired network </li></ul></ul><ul><ul><li>Special bridging software </li></ul></ul>
  36. 37. Access Point
  37. 38. Functions of an Access Point <ul><li>Access point has two basic functions </li></ul><ul><ul><li>Acts as base station for wireless network </li></ul></ul><ul><ul><li>Acts as bridge between wireless and wired network </li></ul></ul><ul><ul><li>Bridges are LAN connectors at MAC level </li></ul></ul><ul><li>See Figure 6-7 </li></ul>
  38. 39. Access Point as a Bridge
  39. 40. Characteristics of an Access Point <ul><li>Range approximately 375 feet (115 meters) </li></ul><ul><li>Generally supports over 100 users </li></ul><ul><ul><li>One access point for each 50 users with light email and basic Internet access </li></ul></ul><ul><ul><li>One access point per 20 users for heavy network access and large file transfer </li></ul></ul><ul><li>APs typically mounted on ceiling, but AC power may be a problem </li></ul><ul><ul><li>Power over Ethernet feature delivers DC power through standard unshielded twisted pair (UTP) Ethernet cable </li></ul></ul>
  40. 41. Ad Hoc Mode <ul><li>Ad Hoc Mode or peer-to-peer mode lets wireless clients communicate among themselves without an access point </li></ul><ul><ul><li>Officially called Independent Basic Services Set (IBSS), this mode is easy to set up, but it does not have access to a wired network </li></ul></ul><ul><ul><li>See Figure 6-8 </li></ul></ul>
  41. 42. Ad Hoc Mode
  42. 43. Infrastructure Mode <ul><li>Infrastructure Mode, also called Basic Service Set (BSS), has wireless clients and an access point </li></ul><ul><li>More access points can be added to create an Extended Service Set (ESS) </li></ul><ul><ul><li>See Figure 6-9 </li></ul></ul>
  43. 44. Extended Service Set (ESS)
  44. 45. Features of Access Points <ul><li>Coverage area should overlap when using multiple access points </li></ul><ul><ul><li>Wireless clients survey radio frequencies to find an AP that provides better service </li></ul></ul><ul><ul><li>A seamless handoff occurs when client associates with new AP </li></ul></ul>
  45. 46. ESS and Subdivided Networks <ul><li>Drawback of ESS WLANs is that all wireless clients and APs must be part of same network to allow roaming </li></ul><ul><li>Network managers like to subdivide networks into subnets, but this prevents clients from roaming freely </li></ul><ul><ul><li>Alternative may be software that tricks network into seeing subnets as one network </li></ul></ul>
  46. 47. Wireless Gateway <ul><li>Devices that follow 802.11 standard are becoming less expensive and more popular </li></ul><ul><li>Wireless Gateway has made future of HomeRF very shaky </li></ul><ul><li>Wireless gateway has wireless access point, Network Address Translator (NAT) router, firewall, connections for DSL and cable modems, and other features </li></ul>
  47. 48. IEEE 802.11 <ul><li>Introduced in 1990 </li></ul><ul><li>Defines cable-free local area network with either fixed or mobile locations that transmit at either 1 or 2 Mbps </li></ul><ul><li>Uses OSI model with functions of PHY and MAC layer performing WLAN features </li></ul><ul><ul><li>See Figure 6-10 </li></ul></ul><ul><li>Slow bandwidth insufficient for most network applications </li></ul>
  48. 49. WLAN features in PHY and MAC layers
  49. 50. IEEE 802.11b <ul><li>1999 amendment to 802.11 standard </li></ul><ul><li>Added two higher speeds: 5.5 and 11 Mbps </li></ul><ul><li>Called Wi-Fi </li></ul><ul><li>Quickly became standard for WLANs </li></ul>
  50. 51. Wireless changes to layers <ul><li>Physical </li></ul><ul><li>Data Link </li></ul>
  51. 52. Physical Layer <ul><li>Physical layer that sends and receives signals from network is divided into two parts </li></ul><ul><ul><li>See Figure 6-11 </li></ul></ul><ul><li>Physical Medium Dependent (PMD) sublayer defines how data is transmitted and received through the medium </li></ul><ul><li>Physical Layer Convergence Procedure (PLCP) performs two basic functions, as seen in Figure 6-12 </li></ul><ul><ul><li>Reformats data into frame PMD sublayer can transmit </li></ul></ul><ul><ul><li>Listens to determine when data can be sent </li></ul></ul>
  52. 53. PHY Sublayers
  53. 54. PLCP Sublayer
  54. 55. Physical Layer Convergence Procedure Standards <ul><li>Based on direct sequence spread spectrum (DSSS) </li></ul><ul><li>Reformats data from MAC layer into frame that PMD sublayer can transmit </li></ul><ul><ul><li>See Figure 6-13 </li></ul></ul><ul><li>Frame has three parts </li></ul><ul><ul><li>Preamble and Header transmit at 1 Mbps </li></ul></ul><ul><ul><li>Data portion, containing from 1 to 16,384 bits, may be sent at faster rate </li></ul></ul>
  55. 56. PLCP Frame
  56. 57. Physical Medium Dependent Standards <ul><li>Frame created by PLCP passes to PMD sublayer where binary 1’s and 0’s are translated into radio signals for transmission </li></ul><ul><li>802.11b standard uses Industrial, Scientific, and Medical (ISM) band for transmissions </li></ul><ul><ul><li>May use 14 frequencies, beginning at 2.412 GHz and incrementing in .005 GHz steps </li></ul></ul><ul><ul><li>See Table 6-1 </li></ul></ul>
  57. 58. 802.11b ISM Channels
  58. 59. Medium Access Control Layer Changes <ul><li>802.11 Data Link layer has two sublayers </li></ul><ul><ul><li>Logical Link Control (LLC), used in 802.11b wireless networks with no change from wired network functions </li></ul></ul><ul><ul><li>Media Access control (MAC) contains all changes necessary for 802.11b WLANs </li></ul></ul>
  59. 60. Two Kinds of Coordination <ul><li>Coordination necessary among devices sharing same RF spectrum </li></ul><ul><li>Two kinds of coordination </li></ul><ul><ul><li>Distributed coordination function is 802.11b standard </li></ul></ul><ul><ul><li>Point coordination function is optional </li></ul></ul>
  60. 61. Distributed Coordination Function <ul><li>Channel access methods refer to different ways of sharing </li></ul><ul><li>Contention </li></ul><ul><ul><li>Computers compete for use of network </li></ul></ul><ul><ul><li>May cause collisions that result in scrambled messages, as seen in Figure 6-14 </li></ul></ul><ul><ul><li>Must first listen to be sure no other device is transmitting </li></ul></ul>
  61. 62. Collision
  62. 63. CSMA/CD <ul><li>802.3 Ethernet standard uses contention with “listening” as channel access method </li></ul><ul><ul><li>Carrier Sense Multiple Access with Collision Detection (CSMA/CD) </li></ul></ul><ul><ul><li>After a collision, each computer waits a random amount of time, called backoff interval, before attempting to resend </li></ul></ul><ul><ul><li>See Figure 6-15 </li></ul></ul>
  63. 64. CSMA/CD
  64. 65. Distributed Coordination Function (DCF) <ul><li>802.11b wireless networks cannot use CSMA/CD because radio signals drown out ability to detect collisions </li></ul><ul><li>802.11b uses Distributed Coordination Function (DCF) with modified procedure known as Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) </li></ul><ul><ul><li>Following collision, clients wait random amount of slot time after medium is clear </li></ul></ul><ul><ul><li>This technique helps reduce collisions </li></ul></ul>
  65. 66. Packet Acknowledgement (ACK) <ul><li>CSMA/CA also reduces collisions by using explicit packet acknowledgement (ACK) </li></ul><ul><ul><li>Receiving client must send back to sending client an acknowledgement packet showing that packet arrived intact </li></ul></ul><ul><ul><li>If ACK frame is not received by sending client, data packet is transmitted again after random waiting time </li></ul></ul><ul><ul><li>Figure 6-16 illustrates CSMA/CA </li></ul></ul>
  66. 67. CSMA/CA
  67. 68. Point Coordination Function <ul><li>Polling, an orderly channel access method, prevents collisions by requiring device to get permission before transmitting </li></ul><ul><ul><li>Each computer is asked in sequence if it wants to transmit, as shown in Figure 6-18 </li></ul></ul><ul><li>802.11b uses an optional polling function known as Point Coordination Function (PCF) </li></ul><ul><ul><li>Beacon frame indicates how long PCF will be used </li></ul></ul><ul><ul><li>If client has nothing to transmit, it returns a null data frame </li></ul></ul>
  68. 69. Polling
  69. 70. Association and Reassociation <ul><li>MAC layer uses association and reassociation to make sure client joins WLAN and stays connected </li></ul><ul><ul><li>Uses either active or passive scanning process </li></ul></ul><ul><ul><ul><li>Passive scanning has client listen for signal containing AP’s Service Set Identifier (SSID </li></ul></ul></ul><ul><ul><ul><li>Active scanning has client send out probe frame and wait for probe response frame from AP </li></ul></ul></ul><ul><ul><li>After locating AP, client sends associate request frame and may join network after receiving frame with status code and client ID number </li></ul></ul>
  70. 71. Reassociation <ul><li>Reassociation involves dropping connection with one access point and establishing connection with another AP </li></ul><ul><ul><li>Allows mobile clients to roam beyond coverage area of single AP </li></ul></ul><ul><ul><li>Allows client to find new AP if original one becomes weak or has interference </li></ul></ul><ul><li>Client scans to find new AP and sends reassociation request frame </li></ul><ul><ul><li>New AP then sends disassociation frame to old AP as shown in Figure 6-19 </li></ul></ul>
  71. 72. Reassociation Process
  72. 73. MAC Frame Formats <ul><li>802.11b specifies three different MAC frame formats </li></ul><ul><ul><li>Management frames—set up initial communication between client and AP, as seen in Figure 6-21 </li></ul></ul><ul><ul><li>Control frames—provide assistance in delivering frame that contains data, as seen in Figure 6-22 </li></ul></ul><ul><ul><li>Data frames—carry information to be transmitted to destination client, as seen in Figure 6-23 </li></ul></ul>
  73. 74. Management Frame
  74. 75. Control Frame
  75. 76. Data Frame
  76. 77. High Speed WLANs <ul><li>Three standards for high-speed WLANs that transmit at speeds over 15 Mbps </li></ul><ul><ul><li>IEEE 802.11a </li></ul></ul><ul><ul><li>IEEE 802.11g </li></ul></ul><ul><ul><li>HiperLAN/2 </li></ul></ul><ul><li>All WLANs are concerned with security </li></ul><ul><ul><li>How to prevent unauthorized access </li></ul></ul>
  77. 78. IEEE 802.11a <ul><li>Approved in 1999, 802.11a transmits at speeds of 5.5 Mbps and 11 Mbps </li></ul><ul><li>Great demand for 802.11a WLANS, also called Wi-Fi5, with maximum speed of 54 Mbps </li></ul><ul><ul><li>Devices use gallium arsenide (GaAs) or silicon germanium (SiGe) rather than CMOS semiconductors </li></ul></ul><ul><ul><li>Increased speed achieved by higher frequency, more transmission channels, multiplexing techniques, and more efficient error-correction </li></ul></ul>
  78. 79. Summary <ul><li>Radio Frequency (RF) wireless local area networks (WLANs) have wide range of uses </li></ul><ul><li>Wireless NIC performs same functions as wired NIC, but it uses antenna to send and receive signals </li></ul><ul><li>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 </li></ul>
  79. 80. Summary <ul><li>Access point (AP) contains three major parts </li></ul><ul><ul><li>Antenna </li></ul></ul><ul><ul><li>Radio transmitter/receiver </li></ul></ul><ul><ul><li>RJ-45 interface to connect by cable to standard wired network by using special bridging software </li></ul></ul><ul><li>AP has two basic functions </li></ul><ul><ul><li>Acts as base station for wireless network </li></ul></ul><ul><ul><li>Acts as bridge between wireless and wired networks </li></ul></ul>
  80. 81. Summary <ul><li>RF WLAN sends and receives data in two different modes </li></ul><ul><ul><li>Ad hoc mode lets wireless clients communicate among themselves without an access point </li></ul></ul><ul><ul><li>Basic Service Set (BSS) infrastructure mode consists of wireless clients and at least one access point </li></ul></ul><ul><li>Can add more access points to increase coverage area and create Extended Basic Service Set (ESS), consisting of two or more BSS wireless networks </li></ul>
  81. 82. Summary <ul><li>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 </li></ul><ul><ul><li>Home RF version 1.0 products, introduced in 2000, transmit at 1.6 Mbps </li></ul></ul><ul><ul><li>Version 2.0, released in 2001, transmits at 10 Mbps </li></ul></ul>
  82. 83. Summary <ul><li>IEEE 802.11 standard defines wireless network, either mobile or fixed, that transmits up to 2 Mbps </li></ul><ul><ul><li>Much too slow for most network applications </li></ul></ul><ul><li>IEEE 802.11b standard quickly became standard for wireless networks when it added two higher speeds: 5.5 Mbps and 11 Mbps </li></ul><ul><li>Physical Layer Convergence Procedure Standard (PLCP) for 802.11b uses direct sequence spread spectrum (DSSS) </li></ul>
  83. 84. Summary <ul><li>The PLCP reformats data from MAC layer into frame that PMD sublayer can transmit. </li></ul><ul><li>Frame has three parts: preamble, header, and data </li></ul><ul><li>802.11b uses Industrial, Scientific, and Medical (ISM) band for transmission at 11, 5.5, 2, or 1 Mbps </li></ul>
  84. 85. Summary <ul><li>802.11b uses Distributed Coordination Function (DCF) access method that specifies a modified Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) procedure </li></ul><ul><ul><li>CDMA/CA makes all clients wait random amount of time following collision </li></ul></ul><ul><ul><li>Reduces collisions by using explicit packet acknowledgements (ACK) </li></ul></ul>
  85. 86. Summary <ul><li>MAC layer of 802.11b standard uses association and reassociation to allow client to join WLAN and stay connected </li></ul><ul><ul><li>Association uses either passive or active scanning to determines whether wireless client or access point should be accepted as part of network </li></ul></ul><ul><ul><li>Reassociation means client drops connection with one access point and reestablishes connection with another AP </li></ul></ul>
  86. 87. Summary <ul><li>802.11b defines power management to conserve battery power without missing data transmissions </li></ul><ul><li>802.11b specifies three different types of MAC frame formats </li></ul><ul><ul><li>Management frames set up communications between client and access point </li></ul></ul><ul><ul><li>Control frames assist in delivering data frames </li></ul></ul><ul><ul><li>Data frames carry information being transmitted </li></ul></ul>
  87. 88. Summary <ul><li>802.11 standard defines three different interframe spaces (PFS) or time gaps </li></ul><ul><ul><li>Rather than being “dead space,” these standard spacing intervals or time gaps between transmission of data frames are used for special types of transmissions </li></ul></ul>
  88. 89. The Wireless Landscape <ul><li>Wireless communication is standard means of communication for people in many occupations and circumstances </li></ul><ul><li>Table 1-1 summarizes wireless technologies, transmission distance, and speed </li></ul><ul><li>Figure 1-14 shows a wireless landscape </li></ul><ul><li>Job market to support wireless technology is already exploding </li></ul>
  89. 90. Wireless Technologies
  90. 91. The Wireless Landscape
  91. 92. Wireless Advantages and Disadvantages <ul><li>Advantages </li></ul><ul><ul><li>Mobility </li></ul></ul><ul><ul><li>Easier and less expensive installation </li></ul></ul><ul><ul><li>Increased reliability </li></ul></ul><ul><ul><li>Disaster recovery </li></ul></ul><ul><li>Disadvantages </li></ul><ul><ul><li>Health risks ? </li></ul></ul><ul><ul><li>Radio signal Interference </li></ul></ul><ul><ul><li>Security </li></ul></ul>
  92. 93. Wireless Advantages <ul><li>Mobility—employees have contact with network; work in teams for better productivity </li></ul><ul><li>Easier and less expensive installation—no need to install cables or modify historical property; easy to remodel office without concern for network access </li></ul><ul><li>Increased reliability—no outages caused by cable failure </li></ul><ul><li>Disaster recovery—easy to relocate office quickly using WLANs and laptop computers </li></ul>
  93. 94. Wireless Disadvantages <ul><li>Health risks?—devices emit small levels of RF </li></ul><ul><ul><li>FDA—inconclusive about safety of wireless devices </li></ul></ul><ul><ul><li>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 </li></ul></ul><ul><li>Radio signal interference--other devices interfere </li></ul><ul><li>Security—some wireless technologies add security such as encryption or coded numbers for authorization to gain access to the network </li></ul>
  94. 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 &quot;gap&quot; 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 &quot;gap&quot; 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
  95. 96. Summary <ul><li>Wireless communications, including Internet connections and networks, are becoming standard in business world </li></ul><ul><li>SWAP connects different devices for home users </li></ul><ul><ul><li>Quickly becoming obselete </li></ul></ul><ul><li>Bluetooth connects some devices over short distances </li></ul><ul><li>WLANs – WiFi 802.11 family </li></ul>
  96. 97. Summary <ul><li>WLANS are fixture of business networks </li></ul><ul><li>WLAN applications found in wide variety of industries and organizations </li></ul><ul><li>Primary advantage of WLAN is mobility or freedom to move without being connected by a cable </li></ul><ul><li>Other advantages include easier and less expensive installation, increased network reliability, and support for disaster recovery </li></ul>
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