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Wireless LANs

WLAN is wireless local area network that use radio waves as its carrier (no physical cabling) Benefits include convenience, ease of installation and maintenance, flexibility WLAN standards define operations using different physical media: infrared and radio-frequency waves.

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Wireless LANs

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  1. WLAN is wireless local area network that use radio waves as its carrier (no physical cabling) Benefits include convenience, ease of installation and maintenance, flexibility WLAN standards define operations using different physical media: infrared and radio-frequency waves. The most common WLAN standard was defined in 1997 as IEEE 802.11 There are numerous revisions/iterations of 802.11 standard Wireless LANs

  2. 802.11 Standard

  3. Wireless media • Radio-frequency transmissions (RF) • Uses low power signal (1 Watt) • Unlicensed bands not regulated by FCC (2.4 or 5.7 Ghz bands) • Infrared • Uses high frequency (just below visible light) signal • Directed (line-of-sight) or diffused signal

  4. Spread Spectrum • It’s a technique where a narrowband signal is deliberately spread in a wider frequency band • Efficient use of bandwidth is sacrificed • Security and integrity of transmission are increased • Effects of EMI are minimized

  5. Frequency Hopping Spread Spectrum • Narrowband signal

  6. Direct Sequence Spread Spectrum • Chipping Code

  7. Direct Sequence Spread Spectrum Wideband signal

  8. Orthogonal Frequency Division Multiplexing • Multi-carrier signal • Many narrowband non-overlapping channels

  9. Infrared 802.11 IR • Defines 1Mbps and 2Mbps operation by bouncing light off ceilings and walls to provide connectivity within a room or small office. • Uses signal in the terahertz (very high) frequency range • Line-of-sight or diffused • Limited range • Higher security (limited to a room) • No RF interference • Lack of vendor conformity to the standard

  10. 802.11 Media Access Control • Main functions defined include controlling media access in a shared network and security (encryption) of transmitted data • CSMA/CA is used to avoid collisions • Developed to overcome a “hidden node” problem

  11. WLAN architecture • Peer-to-peer (adhoc) mode

  12. WLAN Architecture • Infrastructure mode

  13. WLAN architecture • Extended Service Set

  14. 802.11 set of standards

  15. WLAN Security • Wireless transmissions are easy to intercept • WEP->WPA->WPA2(802.11i)

  16. Wired Equivalent Privacy (WEP) • Data encryption for confidentiality • Uses shared symmetric key (same key for encryption/decription) – easy to break • Uses static keys – hard to change, long-lived keys • Uses weak cryptographic algorithm

  17. Wi-Fi Protected Access • Temporary measure to fix WEP vulnerabilities • Was based on developing 802.11i standard • Uses TKIP (Temporal Key Integrity Protocol) for dynamic key distribution • Uses longer keys and stronger encryption algorithm • Implements 802.1x authentication standard and EAP (Extensible Authentication Protocol)

  18. Wi-Fi Protected Access (802.1x support)

  19. WPA2 (802.11i) • Ratified in 2004, integrated into 802.11i-2007 standard • Based on WPA • TKIP • 802.1X • CCMP – for data confidentiality and encryption

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