IWD2243 Wireless & Mobile Security Chapter 1 : Wireless Fundamentals Prepared by : Zuraidy Adnan, FITM UNISEL1

Prepared by : Zuraidy Adnan, FITM UNISEL

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IWD2243Wireless & Mobile Security

Chapter 1 : Wireless Fundamentals


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1.1 Wireless Medium Radio Propagation Effects

Harsh medium for signal propagation Distance between transmitter & receiver Physical environment Relative movement between transmitter & receiver

Attenuation : drop in signal strength as the signal propagates in any medium. Near (1/r2) & Far (1/r4)


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1.1 Wireless Medium (cont.) Shadow fading (slow fading) : Changes in the signal

strength occurring due to the changes in operating environment.

Raleigh fading (fast fading) : Changes in signal strength due to the relative motion of the order of a few centimeters.

Inter-symbol interference – effect of multipath


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1.1 Wireless Medium (cont.) Hidden terminal problem

See figure 1.1b page 6 Collisions of node A and C while reaching B

Exposed terminal problem See figure 1.1c page 7 Node C senses the medium and find it busy since

node B has start transmitting


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1.1 Wireless Medium (cont.) Bandwidth

Bandwidth is always expensive (in wireless) Almost all countries the wireless spectrum is

controlled by government Only certain band are allowed for commercial use All protocol designed revolve around this

constraint Other constraint

Trend – wireless need to be mobile Small devices – limited processing power, limited

battery life


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1.2 Wireless Networking Basics Wireless Local Area Network (WLAN)

1997 – IEEE – 802.11 WLAN standard – 2Mbps 1999 – IEEE – 802.11b – 11Mbps – 2.4Ghz band Small area coverage – office building Security features – encryption, frequency hopping,

firewalls Drawback – high initial cost, limited range,

possibility of mutual interference, the need to security-enabled client

LANs and WLAN – OSI model See figure 1.2 page 10


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1.2 Wireless Networking Basics (cont.)

WLAN – advantages & disadvantages See page 12 & 13 chapter 1

Current WLAN standard 802.11a – 5GHz, compatible with 802.11b Signal interference by 802.11b user 802.11b (Wi-Fi) – 2.4Ghz band – 11Mbps – 4 to 7Mbps Some manufacturers – 802.11b – 22Mbps

Future WLAN standard IEEE – 802.11g – 2.4Ghz band – 54Mbps IEEE – 802.11h – 5Ghz band – 54Mbps – enhancement

of 802.11a – TPC (limit power) – DFS (protect sensitive freq.)


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Bluetooth & WPAN Point to point, point to multipoint piconets – adhoc. Flexible net topology, low energy consumption, robust

data capacity, high quality voice transmission. Speed – 1Mbps, 10 meters

Ultra wideband UWB – > 100Mbps - < 10 meters.


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Security for WLANs 802.11i – security standard for 802.11a,b,g. Replace WEP with TKIP, AES, and 802.1 x

authentication. Incorporated into IEEE 802.11-2007 standard. Wi-Fi alliance – Wi-Fi Protected Assets (WPA), before

802.11i finalized. WEP – 40bit, 60bit, 128bit encryption key. All devices has to be set to use same encryption key. Slow data transfer rate – up to 30%


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SSID – method to identify or name an individual WLAN Service Set Identifier – 32 char unique identifier. Device level pass – connect to BSS – diff 1 WLAN to

another – known also as network name. Step to secure WLAN

See page 17 & 18 chapter 1.


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WLANs performance Transmission speed – file size, number of users,

distance from access points. Performance vary – number of users, local environment,

obstructions that are in the way. WLAN implementation concerns

Planning – Floor plan, site survey Capacity – 1 access point, 15-20 users


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Performance – 802.11b, 350 meters outdoors, very much reduce indoors.

Interference – bluetooth connectivity (handheld device, mobile phones in the same area)

Building work – installation of metal storage cabinets, microwave ovens, fish tanks.

Power consumption – 802.11a, limited power output. Power over Ethernet (PoE) – removing the need to install

additional power cabling.

Documents

IWD2243 Wireless & Mobile Security Chapter 1 : Wireless Fundamentals Prepared by : Zuraidy Adnan, FITM UNISEL1