A comparison of wi-fi and wimax with case studies - Florida State ...
A comparison of wi-fi and wimax with case studies - Florida State ...
A comparison of wi-fi and wimax with case studies - Florida State ...
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The reason that WEP was safe was because the secret key was not easily broken. However<br />
in some <strong>case</strong>s, the network designers use the same shared key for all users. That means that<br />
people can read each other’s packets. That is not good for security. If it is a small network, trying<br />
to use the different keys for each user should not be a big problem, but if it is a big network, for<br />
security reasons, if a secret key changes once in a period <strong>of</strong> time, it is a huge job. How to<br />
distribute a secret key <strong>and</strong> how to assure it is not repeated are very important issues at this point.<br />
Moreover, IV is another potential risk. The WEP protocol recommends that the IV value should<br />
be different for every packet to avoid the keystream attack. If IV is not a r<strong>and</strong>om value, the<br />
encryption <strong>wi</strong>ll be broken easily. Unfortunately some <strong>wi</strong>reless network cards set the initial IV as<br />
0 <strong>and</strong> increase the number by one for each packet sent. With this kind <strong>of</strong> IVs, to break the<br />
encryption is way too easy. Unless the secret key is changed <strong>of</strong>ten or assuring the use <strong>of</strong> r<strong>and</strong>om<br />
<strong>and</strong> different IV for each packet, the risk <strong>wi</strong>ll remain high. If a hacker collects enough packets<br />
<strong>wi</strong>th repeated IV from the same user, the cipher <strong>wi</strong>ll be broken. [17][55]<br />
3.4. The next generation st<strong>and</strong>ard<br />
3.4.1. IEEE 802.11n<br />
IEEE 802.11n is the st<strong>and</strong>ard <strong>of</strong> WLAN for next generation which also called Wi-Fi<br />
(Wireless <strong>fi</strong>delity). This st<strong>and</strong>ard was initiated in 2004 by TGn. The goal <strong>of</strong> this st<strong>and</strong>ard was to<br />
improve the net transmission speed up to 100 Mbps. In the beginning, there were six proposals<br />
that had been posted. After many discussions, there were only two proposals left <strong>and</strong> they were<br />
from TGnSync <strong>and</strong> WWiSE. These two groups have their own support from chip makers.<br />
TGnSync has Athero, Agere, Marvell <strong>and</strong> Intel, while WWiSE has Airgo, Broadcom, Conexant<br />
<strong>and</strong> Texas Instruments. The <strong>fi</strong>rst draft was approved in March 2006 <strong>and</strong> draft 2.0 was approved<br />
in March 2007. Since the dem<strong>and</strong>s from the market are becoming higher, Wi-Fi Alliance decided<br />
to start to certifying IEEE 802.11n products based on the draft 2.0 in summer 2007. Now, these<br />
pre-n products are already in stores, such as routers <strong>and</strong> network cards for desktops or notebooks.<br />
The <strong>of</strong><strong>fi</strong>cial approval <strong>of</strong> IEEE 802.11n st<strong>and</strong>ard had been delayed many times because TGnSync<br />
<strong>and</strong> WWiSE kept <strong>fi</strong>ghting for their own proposal to become the <strong>of</strong><strong>fi</strong>cial st<strong>and</strong>ard. However, they<br />
<strong>fi</strong>nally agreed to propose a merged proposal to speed up the birth <strong>of</strong> <strong>of</strong><strong>fi</strong>cial IEEE 802.11n<br />
st<strong>and</strong>ard. Therefore, the IEEE 802.11n st<strong>and</strong>ard may be <strong>fi</strong>nally approved in early 2008. [17] [65]<br />
[66]<br />
Actually, the ideal <strong>of</strong> these two groups have may be different, but the technologies are the<br />
same. TGnSync emphasizes on improving the peak data rate <strong>and</strong> WWiSE wants to ameliorate<br />
the MAC-layer. Both <strong>of</strong> them can reach the goal, or even much better than that. The common<br />
points are they both use MIMO-OFDM as the transmission function <strong>and</strong> support the b<strong>and</strong><strong>wi</strong>dth<br />
for both 20 MHz <strong>and</strong> 40 MHz. IEEE 802.11n PHY-layer is extended from IEEE 802.11a PHYlayer.<br />
So it is also an OFDM-based PHY-layer <strong>and</strong> just introduced MIMO technology to increase<br />
the speed. [17] [61]-[66]<br />
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