802.11a and g bring more sweet spots for wireless access

In a previous tip, I discussed factors that influence the placement of WAPs. In this tip, I want to explore another factor that isn't often discussed: the difference between the 802.11a

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, 802.11b and 802.11g specifications.

If you ask most people familiar with wireless networking what the difference is, they'll tell you about the data rates, and certainly, the jump from a max of 11Mbps (with b) to 54Mbps (with a or g) is a big deal. However, for network designers, there is another important aspect: the non-overlapping channels. 802.11b and g only have three, which means you can put three WAPs in the same area without interference from each other, while 802.11a has 12 non-overlapping channels. (Note that these numbers are for the U.S. and may vary in other countries.)

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This aspect is critical because many organizations have been toying with the idea of completely replacing their wired infrastructure with cheaper wireless. Previously, this has been impossible because the 802.11 spec is a shared media, which means that the available bandwidth for users in densely populated areas was just unacceptably low.

One other thing you should consider is your existing wireless deployment, which is almost invariably just an addition to the existing LAN switch deployment. Many organizations have deployed 802.11b hardware, and now want to move to 802.11g. As you know, many hardware models are field upgradeable to 802.11a or g, so you may be tempted to simply upgrade to g since it's the most recent spec and leave the WAP in place. The tip here is to avoid this temptation, since it's not necessarily the best move for all environments. Instead, what you should do is a new site survey and consider using 802.11a for areas with higher user density.

With more non-overlapping channels you will probably find that you can manage your frequencies and floorspace much more efficiently, particularly by adding WAPs where you couldn't previously due to overlap. And I suspect that much of the improvement noticed by the users will be due to decreased contention (fewer users on a given WAP) as opposed to just a simple increase in data rates.

Tom Lancaster, CCIE# 8829 CNX# 1105, is a consultant with 15 years experience in the networking industry, and co-author of several books on networking, most recently, CCSPTM: Secure PIX and Secure VPN Study Guide published by Sybex.

This was first published in February 2006

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