Disadvantages of enabling only specific channels for 5GHz wifi

[ecomengineer]

Hi Community,

Continuing with the previous discussion - https://community.cisco.com/t5/wireless/specific-channels-per-wlan-basis-on-cisco-9800/td-p/4838320

I'm using Cisco 9800-40-K9 WLC and C9115AXI-E APs. I have a requirement where the wifi client are medical devices and can connect on only specific 8 channels of 5GHz frequency. If the other channels are broadcasted by the APs on the 5GHz frequency, the medical devices will not connect to the WiFi. So I have configured the RF-tag which is applied to all the APs, to broadcast the 5Ghz frequency on only those particular 8 channels (channel 36, 40, 44, 48, 52, 56, 60 and 64). I have unchecked the other 11 channels in the RF-tag. (refer screenshots of my config vs the default setting).

So my question is, will there be any disadvantage of only allowing only 8 specific channels instead of all 19 channels by default? Will that reduce the Wifi speed or have any impact on the number of devices that can connect to the Wifi? Or any other disadvantages that I can't think of?

[Prince.O · Accepted solution]

Hello,

Yes, the main disadvantage of this will be your channel availability for your deployment. This will likely increase co-channel interference on the wireless network as the APs have less channels to choose from. This won't however, cause data corruption but the down side will be slow connection for clients since WIFI is a polite protocol which will wait it's turn to transmit if other devices detected to be on the same channel.

If you have a small deployment, you can potentially get away with this also depending on the spacing/location of Aps but if you have a dense deployment then this can cause slow connections for clients

[Karsten Iwen · Accepted solution]

One more thing to add: With only a limited amount of channels and a larger amount of APs, you should make sure to stick to 20MHz channels and not use 40 or 80 in your deployment.

[Leo Laohoo]

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@ecomengineer wrote:

I have a requirement where the wifi client are medical devices and can connect on only specific 8 channels of 5GHz frequency.

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That smells like ASCOM.  

Good luck trying to "lock down" the number of channels can be used, particularly in a medical environment, because what happens on paper is totally different in reality.  If ASCOM was really that good, then we would not have be in the middle of complete replacing our ASCOM handsets with Spectralink.

[ecomengineer]

@Leo Laohoo You almost guessed it correct. Not ASCOM but Vocera. I think Spectralink is a product of Vocera

Funny part is, these Vocera badges do support dual band wifi and on all channels, but for some reason (not known to me) the Vocera admins have limited the clients/badges to connect to only 5Ghz and only on those specific 8 channels! God knows why!

[Leo Laohoo]

A medical facility is a "living" site.  Everything changes inside.  Constantly. 

When we started, ASCOM insisted on using 2.4 Ghz when we were already implementing 5.0 Ghz for voice calls.  It took a long time to drag ASCOM to the table, kicking and screaming like a girl, before reluctantly agreeing to investigating about using 5.0 Ghz for voice. 

The reason why ASCOM dictate using 4 UNII-1 and 4 UNII-3 channels is because their batteries will get drained if they scan UNII-1, -2, and -3 channels.

And this is also the reason why WiFi RFID never really took off.