Dynamic Frequency Selection of channel assignment for APs in high density areas

[gunnar_amundson]

We have Ruckus ZF7263's at our hotel. Our vendor installed the APs with the auto configuration for channel settings. After doing a wireless survey I noticed that there were several adjacent APs assigned to the same channel. It seems from this observation that the auto assignment of channels doesn't always do a good job of assigning the channels. Is there a reason why I would have 6 adjacent APs would be assigned to the same channel? It seems that Dynamic Frequency Selection isn't the ideal way to setup APs in high density locations. Is it your recommendation to manually configure the channels instead of relying on DFS?

[john_d]

Do you mean DFS or ChannelFly or Background Scanning? DFS isn't really a channel selection algorithm — it's a method for using channels with radar restrictions.

In my experience, it's not unusual even with ChannelFly to have adjacent AP's using similar channels if there's not a lot of network load — each AP observes good capacity on the channel. However, once an AP starts heavily using the channel, the others sharing the same channel will observe the sudden decrease in capacity and switch away from the channel.

[gunnar_amundson]

I'm talking about the dynamic channel assignment (channels 1-11) for the 2.4GHz frequency. So that would be DCA, not DFS. You are correct, DFS detects radar interference on the 5GHz frequency.

What I'm seeing at a lot of our hotels is the vendors are using the auto setting for channel assignment. Then on my surveys I see the technology doesn't really work that well as I'm see adjacent APs assigned to the same channel instead of a non-overlapping channels. Perhaps the auto setting is good for some environments, but not all. I'm getting mixed results, especially in high density AP deployments.

[john_d]

Ok, so it sounds like you're using ChannelFly to dynamically assign channels. ChannelFly is a statistical analysis algorithm based off actual observations of throughput on your network, not based off conventional heuristics (such as assign adjacent AP's non-overlapping channels).

In my opinion while it has its limitations and caveats, it does tend to be quite effective, especially in the real world where rogue AP's and other external circumstances generate 2.4GHz interference outside your control.

I'd recommend dumping the support info for your AP's to inspect the historical channel capacity statistics, to see if you agree with ChannelFly's observed throughputs on other channels. It might not be as disadvantageous as you might think for adjacent AP's to use the same channel, if the load is light and the other channels have even worse throughput.

The ChannelFly algorithm always chooses the channel with the highest observed throughput potential.

[monnat_systems]

Ideal way to setup APs in high density locations is to use channelfly algorithms however using this features has its own caveats as this feature runs real time and make real quick decisions when it sees a another channel with a significant performance increase. this triggers a wave of client disconnects. As per my experience, Legacy devices get stuck, computer need to rebooted to bring WNIC to life or WNIC need to disabled or enabled. this happened to me, users slow WNIC can't see SSID as AP is channel hopping using channelfly

take a middle path where you increase the MTBC of channelfly feature where "you" dicate how often you want AP to change channel rather that random which creates more trouble than solving.

PS: i get quite a few support call for AP running channel fly in non-high density environments.