Q

Channel overlap

I am implementing a wireless network on a small campus (five acres; 10 buildings). I have been told that the network should be set up with each access point given the same SSID name and set to a different channel. I've also been told that channels can overlap and therefore not to utilize more than three channels. Can you verify this for me? Also, I have been told that rather than using five or six access points, I should use one good one and augment it with repeaters. Can you comment on this?
If you're using 802.11b or 802.11g, there are 11 different channels defined for use in the United States. However, many of those channels overlap with each other. To avoid co-channel interference, you should use the three non-overlapping channels 1, 6, and 11. If you use channels that are closer together, interference will cause some packet loss. Actual loss will depend on utilization. Many adjacent unrelated WLANs do operate on overlapping channels -- they just don't operate as efficiently as they could with better channel separation.

To do this, you should position your APs so that adjacent APs use non-overlapping channels. For example, place the AP on channel 1 next to APs using channels 6 and 11. The AP using channel 6 should be next to APs using channels 11 and 1. And so on. The coverage area of each AP should overlap with the next AP enough to avoid leaving holes, but not so much that stations bounce back and forth between adjacent APs. (Stations automatically...

roam to the AP with the strongest signal.) To learn more about WLAN layout, I recommend reading the CWNA Study Guide from Planet3 Wireless.

That guide also discusses the use of wireless repeaters. Repeaters are primarily useful when you don't have wired network access for all of your access points. Repeaters let you use wireless to connect your APs to each other. If wired network access is readily available in the locations where you want to place your APs, then repeater mode is not your best option.

This was first published in February 2004

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