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Wireless Local Area Networks

Wireless Local Area Networks. By Edmund Gean August 2, 2000. Why Wireless?. extension of wired LAN alternative for a wired LAN ease of installation mobile users. Wireless Terminology. WLAN 802.11 basic service set (BSS, cell) DSSS vs FSSS

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Wireless Local Area Networks

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  1. Wireless Local Area Networks By Edmund Gean August 2, 2000

  2. Why Wireless? extension of wired LAN alternative for a wired LAN ease of installation mobile users

  3. Wireless 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

  4. 802.11 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

  5. ISM Frequency Bands

  6. Physical 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.

  7. DSSS vs FHSS

  8. Media 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

  9. Compaq Wireless Equipment

  10. Configuration Peer-to-peer (ad-hoc) mode Infrastructure mode

  11. Ad-Hoc Mode

  12. Infrastructure Mode

  13. Software Access Point

  14. Infrastructure Mode with Hardware Access Point

  15. Infrastructure Mode with Multiple Hardware Access Points

  16. 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

  17. Demonstration

  18. Conclusion • interoperability of WLAN networking equipment • use of WLAN at Cal State LA

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