What Is a WLAN?
As stated in the beginning of the chapter, WLANs are networks that are commonly deployed in places such as corporate office conference rooms, industrial warehouses, Internet-ready classrooms, and even coffeehouses. A WLAN uses radio frequency (RF) technology to transmit and receive data over the air, in a manner defined by the predominant standard for wireless IEEE 802.11.
These IEEE 802.11-based WLANs present new challenges for network administrators and information security administrators. Unlike the relative simplicity of wired Ethernet deployments, 802.11-based WLANs broadcast RF data for the client stations to hear.
To understand some of the challenges and weaknesses, an explanation of the protocol stack and the wireless functionality is in order. Figure 14-4 illustrates the 802.11 standard protocol stacks for a client-server application over a wireless network.
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14-4 802.11 Protocol Stack
The IEEE 802.11 standard specifies the over-the-air interface between a wireless client and a base station or access point. The standard also specifies the interface for connections among wireless clients. As with any other 802.x standard (802.3 is Ethernet, 802.5 is Token Ring), the 802.11 standard provides specifications to address both the physical (PHY) and medium access control (MAC) layers.
The 802.11 standard was first released in 1997. It specified the MAC sublayer, MAC management protocols and services, and three physical layers providing different data rates. Later releases have improved data rates, security features, and quality of service features. Table 14-1 compares the main differences between the different standards.
Table 14-1 Overview of 802.11 Standards
|
|
802.11a |
802.11b |
802.11g |
|
Frequency |
5 GHz |
2.4 GHz |
2.4 GHz |
|
Rate |
54 Mbps |
11 Mbps |
54 Mbps |
|
Market |
Home entertainment |
Wireless office |
Home and office applications |
The data sent according to the 802.11a and 802.11g standards is transmitted at the same rate, but the 5-GHz band has some restrictions and is not as clear as the 2.4-GHz band in some countries. Other 802.11 specifications do exist and are being worked on. This chapter, however, focuses on the 802.11i standard, which is an 802.11 MAC enhancement to provide improved security and authentication mechanisms.
In summary, it is possible to say that, at this moment, the most popular WLAN is the 802.11b used for initial applications in the business world. On the other hand, residential applications are forecast to explode in the coming years, most likely making 802.11a the de facto wireless standard.