Wireless Local Area Networks By Edmund Gean August 2, 2000.
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Transcript of Wireless Local Area Networks By Edmund Gean August 2, 2000.
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Wireless Local Area NetworksWireless Local Area Networks
By Edmund Gean August 2, 2000
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Why Wireless?Why Wireless?
• extension of wired LAN
• alternative for a wired LAN
• ease of installation
• mobile users
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Wireless TerminologyWireless Terminology
• WLAN• 802.11• basic service set (BSS, cell)• DSSS vs FSSS• Hardware vs Software Access Points• channel• SSID• peer-to-peer mode• infrastructure mode
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802.11802.11
• IEEE 802.11 standard created in 1997 to facilitate interoperability between differing brands of wireless LANS
• specifies 2 Mbps data rate with fallback to 1 Mbps
• IEEE 802.11 High Rate standard ratified in 1999 allows 11 Mbps (backward compatible to 802.11)
• allows choice of different physical layers. Vendors use either frequency hopping spread spectrum (FHSP) or direct sequence spread spectrum (DSSS)
• specifies medium access control (MAC) and physical characteristics for wireless LANs
• radio frequencies in range of 2.4 GHz - 2.483 GHz
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ISM Frequency BandsISM Frequency Bands
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Physical LayerPhysical Layer• Direct Sequence Spread Spectrum
- employs a high speed code sequence, along with the basic information being sent, to modulate a RF carrier.
- 20 MHz bandwidth per channel
- 11 overlapping Channels in US
- 3 non-overlapping channels•Frequency Hopping Spread Spectrum- uses a code sequence to "hop" from frequency to frequency over a wide band.
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DSSS vs FHSSDSSS vs FHSS
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Media Access Control LayerMedia Access Control Layer
•Uses Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)
- distributed inter frame space (DIFS)
- exponential random backoff time
- short inter frame space (SIFS)
- no collision detection (hidden node problem)
- collision avoidance via RTS/CTS frames
•similar to CSMA/CD in standard IEEE 802.3 Ethernet
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Compaq Wireless EquipmentCompaq Wireless Equipment
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ConfigurationConfiguration
•Peer-to-peer (ad-hoc) mode
•Infrastructure mode
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Ad-Hoc Mode
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Infrastructure Mode
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Software Access Point
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Infrastructure Mode with Hardware Access Point
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Infrastructure Mode with Multiple Hardware Access Points
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Configuring Wireless Network using Compaq Wireless Hardware Access Point•install Access Point Manager
•install hardware access point
•configure hardware access point using AP Manager (IP address, channel #, community string)
•install wireless PC card into PCMCIA slot of notebook
•install wireless drivers onto notebook
•set value of Service Set Identifier (SSID) same as that of hardware access point
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Demonstration
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ConclusionConclusion
• interoperability of WLAN networking interoperability of WLAN networking equipmentequipment
• use of WLAN at Cal State LAuse of WLAN at Cal State LA