Forum

Ryan,
My guess is that the best answer to your question depends upon the population of client devices. If you have a high percentage of 802.11n devices (maybe 80% or better), you might benefit more from 40 MHz channels. If you can justify using more APs with 20 MHz channels, your aggregate system capacity will still be good as a result of low co-channel interference and smaller service areas with consistently high data rates...especially if you have high client-to-AP ratios, as you might expect in a dorm, classroom, library, lecture hall, etc. Channel bonding is the single most effective 11n feature to increase bandwidth though.

I thought someone else would chime in with some hard data by now.

Also, I'm curious if you're avoiding DFS channels because of client support (with such a diverse and uncontrolled client population) or because you expect actual DFS events to trigger channel changes and brief outages. If the latter, give your vendor another 6 months. By the end of this year, they'll have released their spectrum analysis functionality within the AP and DFS testing should be more accurate.

Andy P,
No, DFS is not the same as Cisco's Dynamic Channel Assignment. Dynamic Frequency Selection is a requirement introduced with 802.11h that requires Wi-Fi devices in certain 5 GHz frequency bands to scan for radar (military, weather, etc.) and avoid interfering with radar. In some environments, the presence of radar can really ruin your WLAN channel plan and limit your capacity. Dynamic Channel Assignment is a way to automate the transmit power and channel selection process so that the infrastructure controls it dynamically and the IT staff doesn't have to manually plan and configure these elements.

Wlanman,
Many people are just avoiding it at this point. In order to gain DFS compliance, WLAN vendors must detect all radar events, but spectrum resolution in the AP is not really good enough to ensure low rates of false positives. So, you get lots of false DFS events because vendors have to be extra "sensitive." Hopefully, integrating spectrum analysis in the AP will improve DFS detection. Cisco never confirmed this fact when I asked them about CleanAir, but I'm pretty sure its many times more accurate. Aruba will be in similar shape (though resolution won't be as good) later this year (if their timeline projections were legitimate). So, I suppose that is the "effect" of DFS. :)