Wireless LANs - PowerPoint PPT Presentation

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Wireless LANs

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WLAN is wireless local area network that use radio waves as its carrier (no physical cabling) Benefits include convenience, ease of installation and maintenance ... – PowerPoint PPT presentation

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Title: Wireless LANs


1
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.
  • The most common WLAN standard was defined in 1997
    as IEEE 802.11
  • There are numerous revisions/iterations of 802.11
    standard

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
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5
Spread Spectrum
  • Its 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

6
Frequency Hopping Spread Spectrum
  • Narrowband signal

7
Direct Sequence Spread Spectrum
  • Chipping Code

8
Direct Sequence Spread Spectrum
  • Wideband signal

9
Orthogonal Frequency Division Multiplexing
  • Multi-carrier signal
  • Many narrowband non-overlapping channels

10
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

11
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

12
WLAN architecture
  • Peer-to-peer (adhoc) mode

13
WLAN Architecture
  • Infrastructure mode

14
WLAN architecture
  • Extended Service Set

15
802.11 set of standards
Wi-Fi specifications Wi-Fi specifications Wi-Fi specifications Wi-Fi specifications
Specification Speed Frequency Compatible
Specification Speed Band with
802.11b 11 Mb/s 2.4 GHz b
802.11a 54 Mb/s 5 GHz a
802.11g 54 Mb/s 2.4 GHz b, g
802.11n (draft) 248 Mb/s 5 GHz and/or 2.4 GHz b, g, n
16
WLAN Security
  • Wireless transmissions are easy to intercept
  • WEP-gtWPA-gtWPA2(802.11i)

17
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

18
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)

19
Wi-Fi Protected Access (802.1x support)
20
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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