Wireless Local Area Networks By Edmund Gean August 2, 2000.
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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 Hardware vs Software Access Points channel SSID peer-to-peer mode infrastructure mode
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
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.
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
Infrastructure Mode with Multiple Hardware Access Points
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