Wireless LANs WLAN is wireless local area network

Wireless LANs Ø WLAN is wireless local area network that Ø Ø 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 1

802. 11 Standard 2

Wireless media Ø Radio-frequency transmissions (RF) q Uses low power signal (1 Watt) q Unlicensed bands not regulated by FCC (2. 4 or 5. 7 Ghz bands) Ø Infrared q Uses high frequency (just below visible light) signal q Directed (line-of-sight) or diffused signal 3

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Spread Spectrum Ø It’s a technique where a narrowband signal is deliberately spread in a wider frequency band Ø Efficient use of bandwidth is sacrificed Ø Security and integrity of transmission are increased Ø Effects of EMI are minimized 5

Frequency Hopping Spread Spectrum r Narrowband signal 6

Direct Sequence Spread Spectrum r Chipping Code 7

Direct Sequence Spread Spectrum Wideband signal 8

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

Infrared 802. 11 IR r Defines 1 Mbps and 2 Mbps operation by bouncing light off ceilings and walls to provide connectivity within a room or small office. r Uses signal in the terahertz (very high) frequency range r Line-of-sight or diffused r Limited range r Higher security (limited to a room) r No RF interference r Lack of vendor conformity to the standard 10

802. 11 Media Access Control r Main functions defined include controlling media access in a shared network and security (encryption) of transmitted data r CSMA/CA is used to avoid collisions r Developed to overcome a “hidden node” problem 11

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

WLAN Architecture r Infrastructure mode 13

WLAN architecture r Extended Service Set 14

802. 11 set of standards Wi-Fi specifications Specification Frequency Compatible Band with Speed 802. 11 b 11 Mb/s 2. 4 GHz b 802. 11 a 54 Mb/s 5 GHz a 802. 11 g 54 Mb/s 2. 4 GHz b, g 248 Mb/s 5 GHz and/or 2. 4 GHz b, g, n 802. 11 n (draft) 15

WLAN Security r Wireless transmissions are easy to intercept r WEP->WPA 2(802. 11 i) 16

Wired Equivalent Privacy (WEP) r Data encryption for confidentiality r Uses shared symmetric key (same key for encryption/decription) – easy to break r Uses static keys – hard to change, long-lived keys r Uses weak cryptographic algorithm 17

Wi-Fi Protected Access r Temporary measure to fix WEP vulnerabilities r Was based on developing 802. 11 i standard r Uses TKIP (Temporal Key Integrity Protocol) for dynamic key distribution r Uses longer keys and stronger encryption algorithm r Implements 802. 1 x authentication standard and EAP (Extensible Authentication Protocol) 18

Wi-Fi Protected Access (802. 1 x support) 19

WPA 2 (802. 11 i) r Ratified in 2004, integrated into 802. 11 i-2007 standard r Based on WPA r TKIP r 802. 1 X r CCMP – for data confidentiality and encryption 20