Chapter 6. The Wireless LAN Solution

The modern world is full of wireless communication systems. To mention a few, there are broadcast radio and TV, dispatch radio, cellular phones, walkie-talkies, and, of course, cordless phones within households. Consider the flexibility, mobility, and convenience that these communication systems offer. There is no need to be stationary or physically connected to a particular communication system to use it. You can listen to a radio while traveling in a car, speak on a mobile phone while navigating crowded sidewalks of a major city, or freely move around your kitchen making dinner while chatting with a friend on a cordless phone.

Yet, like all wire-based communication systems, wireless communications have their inherent and unique limitations. To gain a practical understanding of some of these limitations, try using your cellular phone outside the coverage area, walk too far away from the base unit antenna in the middle of a conversation on a cordless phone, or have your nerve endings frayed by static and interference while trying to tune into a radio station that is being jammed or that is a bit out of range. Also, if your credit card bill shows strange charges after you've given a merchant your credit card information using a mobile phone, you will gain a greater appreciation of how easy it is to intercept cellular communications and to take advantage of information that is transmitted through the air.

Notwithstanding any of these limitations, the growing popularity and widespread use of wireless technologies prove not only their marketplace appeal but also their commercial viability. The same holds true for wireless local-area networks (WLANs). WLANs began to emerge in the networking arena (initially with limited success) in the mid-1990s, spurred by the work of IEEE that led to the publication in 1997 of the 802.11 standard. However, the 1 to 2 Mbps data rates as specified in the 1997 802.11 standard were at that time significantly below the rates of the mainstream 10/100 and the emerging Gigabit Ethernet. Thus, the limited initial acceptance of WLANs! That's not so anymore, but it's a winding road.

In 1999, the 802.11 standard was updated and further supplemented by two additional WLAN standards (802.11a and 802.11b) offering higher data rates but lacking compatibility with each other. 802.11b specified the continued use of 2.4-GHz frequency bands, as in the original 802.11. It also specified data rates of up to 11 Mbps thanks to a more efficient modulation scheme known as the complementary code keying (CCK). 802.11a specified the use of the 5-GHz bands with data rates up to 54-MHz using the multicarrier system of orthogonal frequency division multiplexing (OFDM) and several relevant modulation techniques to support the higher data rates. From the perspective of the network end user and the designer, WLAN performance improved and choices increased, but confusion mounted.

There is hope! The promise of reconciliation between 802.11a and 802.11b now lies in the 802.11g standard, which incorporates the 802.11a OFDM system to achieve data rates of 54 Mbps, uses the 2.4-GHz bands, and also requires the implementation of 802.11b modulation techniques. This makes 802.11g backward compatible with 802.11b and potentially avoids regulatory issues in some countries that are associated with the use of the higher frequencies in the 5-GHz bands.

Needless to say, WLANs come to the networking world with their share of capabilities, limitations, and a measure of confusion. The confusion stems not only from the 802.11a/b incompatibilities but also from the availability of a relatively large number of different security-related protocols that have been implemented to compensate for the initial WLAN shortcomings in the area of security. Such is the price of progress.

However, any of the perceived WLAN limitations should not be cause for avoiding WLAN deployment. They can be readily overcome when, in the course of a WLAN design, proper consideration is given to the issues of standards, performance, topology, and the desired level of security.

When deployed judiciously, WLANs introduce into data networking and telecommunications the same degree of convenience, flexibility, and mobility that some of the other wireless technologies bring into other aspects of our lives. This chapter addresses the design and deployment of an SMB WLAN solution in the context of the following major topics:

• WLAN-specific security considerations

• WLAN performance and topology considerations

• WLAN components

• The Cisco WLAN (Aironet) products family

• WLAN deployment scenarios