Wireless Client cannot see the Access Point

I often get contacted regarding wireless clients not working in an area where there is a known access point. When I get into the controller, I never find a problem. The access point and the radio’s all show up. These clients are always using 802.11a, I have never had this problem using 802.11b/g, but it’s still possible to have this issue..

I often find that by changing the channel on the access point resolves the issue. This can be due to a couple different issues, but often has the same root cause.

On a Cisco Wireless LAN Controller (WLC) there are 21 channels that can be used. I have found that some clients do not support all 21 channels. When the WLC is allowed to use the default Dynamic Channel Allocation (DCA) settings, there is a good chance that there are channels allowed to be used that are not supported by the client. You can change these allowed channels under Wireless –> 802.11a/n –> DCA, then it’s under “DCA Channels”. You only want the supported channels listed in this field. If there is a channel in this field that is not supported by your client, it won’t work on the AP’s that use that channel.

I had a client that had set their Cisco 7921G wireless phones to only support channels 36, 44, 157, 165. A user noticed that the phone didn’t work in a couple of areas. After some digging, we found out that channel 161 was in the DCA list. Simply removing it and giving the system time to adjust resolved the problem.

Instead of checking for Co-Channel interference or replacing Access Points, check the channels first, it may be an easy fix for you.

Have you run into this before?
What client had the issue and what channels didn’t it support?

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