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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

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wireless local area networks

Wireless Local Area Networks

By Edmund Gean August 2, 2000

why wireless
Why Wireless?

extension of wired LAN

alternative for a wired LAN

ease of installation

mobile users

wireless terminology
Wireless Terminology



basic service set (BSS, cell)


Hardware vs Software Access Points



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
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
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

Peer-to-peer (ad-hoc) mode

Infrastructure mode

configuring wireless network using compaq wireless hardware access point
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

  • interoperability of WLAN networking equipment
  • use of WLAN at Cal State LA