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Designing a WLAN for a high school using 802.11g

Understand AP planning after our WLAN expert, Mike Puglia, walks you through some steps in his response to how you can design a WLAN using 802.11g.

I am trying to design a WLAN for a high school using 802.11g. I understand my channel considerations so our plan is to position the APs so that channel overlap is minimized. We have roughly one AP per three classrooms, but this would mean the possibility of 75 computers hitting AP. I know there are many variables to consider, so I just don't know if it is possible to do this. Any suggestions?

AP planning can be difficult, as your example demonstrates. No matter how many users a vendor claims to support, you really don't want more than 20-25 users on a single AP at any time due to contention over the air. With 802.11b/g there are three, non-overlapping channels (1,6,11), so you want to deploy APs in a fashion so that there are no overlaps of APs running on the same channel. One can accomplish this in a number of ways:

  1. Most APs allow you to adjust power settings. So, you can lower the power settings to get smaller areas of coverage and a more dense deployment of APs and use a site survey tool to confirm your coverage.
  2. Most Enterprise AP/Controllers come with dynamic RF algorithms where they will automatically adjust the power and channel of individual APs in order to minimize interference.
  3. Planning software: A number of vendors make predictive modeling software just for this purpose. You import a floor plan, put in the number of users, etc. and it will calculate the best placement for your APs in order to meet your specific environmental conditions (number of users, floorplan layout, etc). Companies such as AirMagnet, Motorola and Bluesocket make such software.

This was last published in October 2006

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