Title: Wireless LANs
1Wireless 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
2802.11 Standard
3Wireless 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(No Transcript)
5Spread 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
6Frequency Hopping Spread Spectrum
7Direct Sequence Spread Spectrum
8Direct Sequence Spread Spectrum
9Orthogonal Frequency Division Multiplexing
- Multi-carrier signal
- Many narrowband non-overlapping channels
10Infrared 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
11802.11 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
12WLAN architecture
- Peer-to-peer (adhoc) mode
13WLAN Architecture
14WLAN architecture
15802.11 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
16WLAN Security
- Wireless transmissions are easy to intercept
- WEP-gtWPA-gtWPA2(802.11i)
17Wired 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
18Wi-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)
19Wi-Fi Protected Access (802.1x support)
20WPA2 (802.11i)
- Ratified in 2004, integrated into 802.11i-2007
standard - Based on WPA
- TKIP
- 802.1X
- CCMP for data confidentiality and encryption