1. Wireless LAN Network Security

2. About WLAN • IEEE 802.11 standard • Use wireless transmission medium such as radio, microwave, infrared to provide network connectivity • An Access Point (AP) is installed to act as Bridge between wireless and wired Network • The AP is connected to wired network and is equipped with antennae to provide wireless connectivity • Range (distance between AP and WLAN client) depends on structural hindrances and RF gain of the antenna at the AP • A client is always associated with one AP and when the client moves closer to another AP, it associates with the new AP • Three flavors: 802.11b, 802.11a, 802.11g, etc. Network Security

3. 802.11 Architecture • Access Point (AP): • Any entity that has station functionality & provides access to distributed system • They transmit and receive radio frequencies • Basic Service Set (BSS): • Set of stations controlled by a single coordination function • Every BSS has an identification (ID) called the BSSID which is the MAC address of the AP servicing the BSS Network Security

4. Architecture continued • Extended service set (ESS): A set of two or more connected BSSs with APs connected through a Distribution System. Each ESS has an ID called the ESSID which is a 32-byte character string. • Distribution system (DS): Connects APs in an ESS. The concept of a DS can be used to increase network coverage through roaming between cells. Network Security

5. Services • Services provided by distribution system: • Distribution • Integration • Association • Re-association • Disassociation • Services provided by stations: • Authentication & de-authentication • Privacy • Data delivery Network Security

6. Station types • No-transition • A station is either stationary or moving only inside a BSS • BSS-transition • A station can move from one BSS to another, but inside one ESS • ESS-transition mobility • A station can move from one ESS to another Network Security

7. WLAN Protocol Architecture Network Security

8. MAC Sublayers - DCF Distributed Coordination Function • It uses CSMA/CD, contention based (without pre-coordination) • The “listen before talk" operating procedure (first sense then transmit) • Before sending a frame, the source station senses the medium. After a station is found to be idle, the station waits for a period of time DIFS – Distributed InterFrame Space; then the station sends a control frame called RTS – Request to send • After receiving RTS and waiting for period of time SIFS – Short interframe space, the destination station sends control frame CTS – clear to send back to source. It indicates that destination is ready to receive data • The source station sends data after waiting for amount of time equal to SIFS • The destination sends ACK to ensure delivery of frame Network Security

9. MAC Sublayers - PCF Point Coordination Function • Optional access method, works only in infrastructure network • High priority than DCF • A centralized contention-free polling access method • AP performs polling of stations one after another • To give priority to PCF over DCF: PIFS (PCF IFS) and SIFS are defined • SIFS is same as in DCF • PIFS is shorter than DIFS: If at the same time, a station wants to use only DCF and AP wants to use PCF, AP gets priority Network Security

10. WLAN Benefits • Convenience • Mobility: Nomadic access • Productivity • Deployment • Expandability • Low Cost: no wiring required • Robust Network Security

11. WLAN disadvantages • Security • Range • Reliability • Speed • Radio emissions • Hidden and exposed station problem Network Security

12. WLAN : 802.11b • The most popular 802.11 standard currently in deployment. • Supports 1, 2, 5.5 and 11 Mbps data rates in the 2.4 GHz ISM (Industrial-Scientific-Medical) band Network Security

13. WLAN : 802.11a • Operates in the 5 GHz UNII (Unlicensed National Information Infrastructure) band • Incompatible with devices operating in 2.4GHz • Supports Data rates up to 54 Mbps. Network Security

14. WLAN : 802.11g • Supports data rates as high as 54 Mbps on the 2.4 GHz band • Provides backward compatibility with 802.11b equipment Network Security

15. Standards in process • 802.11ac : <6GHz throughput (Dec 2013) • 802.11ad : 60 GHz throughput (Dec 2012) • 802.11af : TV whitespace (Jun 2014) • 802.11ah : 1 GHz throughput Sensor Network (May 2015) • 802.11ai : Fast initial link setup (Sep 2014) Network Security

16. Recommended Reading • WLAN MAC layer frame format & frame types • Physical layer specifications: IEEE 802.11 FHSS, DSSS, Infrared, OFDM etc • Network Allocation Vector • WEP security service • Wireless transmission media • Bluetooth architecture & frame format • CSMA, ALOHA Network Security