What are the 5Ghz non-DFS, non-overlapping channels?

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What are the 5Ghz non-DFS,  non-overlapping channels?
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Laura

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Posted 4 years ago

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John

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Laura:

Not all of the channels in the 5 Ghz band are useable all of the time.  If you are near an airport then some of the 5 Ghz channels are not available to you.  DFS stands for Dynamic Frequency Selection so basically you have that feature turned on and your APs will listen for Radar or first responders using those 'shared' frequencies and not use those channels if they are being used.

Check this out.

John

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Ronald Dvorak, Embassador

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I'm not an expert on the US regulatory domain so here a link to wikipedia...
http://en.wikipedia.org/wiki/List_of_WLAN_channels

The 5GHz channels don't overlap, BUT if you use channel bonding for 802.11n or 802.11ac to bond more channels to a 40 or 80 MHz channel you'd need to make sure you don't overlap.

In the latest controller version the GUI also show which of your 5GHz channels are non-DFS - just choose custom channel plan and you get the list.
The below screenshot is for AP country set to Austria ...

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Laura

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Thanks,
We use the non DFS channels: 36, 40, 44, 48, 149, 153, 157, 161
At some schools we use 40Mhz and other school use 20Mhz. I don't know why.
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Walfs Adam

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Which country do you live?
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Here another slide that illustrate how channel width affects the available non-overlapping channels...

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Laura

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So if I were to use 5Ghz, non overlapping.  non DFS channels at 40MHz, I could use 36 , 44, 149, and 157? Would that work?
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Hartmut Sachse

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Thats  right. In this case you bond channels to 40 MHz channels with the upper channel selected as second channel. This results in bonding of channel 36 with 40, 44 with 46, 149 with 153 and 157 with 161. This creates a 4 channels (like a 4 channel plan) usable to develop a non-overlapping channel sheme. 

Any reasons why you don't want use DFS channels? If you need smaller cell size design (voice over wifi or high density setup require this) using all available channels is i most case required to prevent channel overlapping. I some case using only 20 MHz channels even for 802.11a/n (5 GHz) is needed for scalability and higher performance even with a lower max. PHY rate thats possible with 20 MHz.

What application do you design your wifi for?  
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Laura

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We use Enterasys 3605 APs. Most of the schools, Radio 1 is set to 40MHz and Radio 2 is set to 20MHz. But at one school, I noticed both radios were set to 20MHz, Not sure why, but I changed it to see if it improves anything. We have an Enterasys AP in most classrooms above the ceiling tile in the center of the room, so that seems like plenty of coverage, but we still get teachers complaining that there wifi connection drops when using iPads, or cannot mirror to an Apple TV from their Ipad or macbook air. Sometimes when teachers try to mirror to their Apple TV, it doesn't show up in the list as an option.
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Laura

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I don't see neighboring APs on the same channel either.
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Hartmut Sachse

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Sometimes using only 20 Mhz channel for both frequency band make the connections more stable. Older iPads and iPhones (other tablets/smartphones, too) only have 2,4 GHz radios so they could only use 802.11g/n. To save battery energy many mobile device have only 1x1:1 MIMO wifi module and only support 20 MHz channels. So this devices have a max PHY rate of 150 mbps (around 65-75 mbps throughput in reality). This bandwidth is shared by all clients connected to this radio.

But the connection drops sounds like another problem. Maybe and non-wifi interferer like bluetooth. Do you have a spectrum analyser for troubleshooting?
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Laura

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What is a good free spectrum analyzer program? or low cost
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Hartmut Sachse

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I only now there is one free open source project, but this even require a commercial spectrum analysis adapter. The cheapest solution would be to buy a standalone from a big competitor starting with C of Extreme and use there free available spectrum analyser software.

Another solution for a nice price is Metageek Chanalyzer.  Maybe you could rent a spectrum analyzer because interpreting the results is the challenge for most beginners.
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Laura

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Thanks for all the info. Since we have the enterasys 3605 APs, there are 2 radios. one is set to g/n 20MHz and one is set to a/n 40MHz. When i get an AP up and running and attach to it, my transmit rate on my MacAir says its 300Mbps. Does that mean I am sharing that 300Mbps with everyone else that is on the same radio as me? I dont actually get 300 Mbps to my self, do I?

Each radio should be transmitting 300Mbps, which is just the connection from the wireless device to the Access Point.
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Yes, that is correct, the medium air is shared with all devices on the same channel.
This is why you shouldn't have more then 1 AP in the same area with the same channel configured as they would share the medium.

Also please keep in mind that it's a half duplex medium so only one client could tx or you have a collision .... like a hub in the good old days.

As a result you'll never see a thruput of 300Mbps on your client... I assume about 150Mbs if you test with iperf (https://iperf.fr/) and more then one stream.
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Hartmut Sachse

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Like Ronald told you at 300 mbps PHY rate you could assume about 145-150mbps throughput with iperf (udp) for a device like a laptop with a wifi adapter 2x2:2 MIMIO or better. Most tablets only have 1x1:1 MIMO wifi adapter limiting there speed to around 65 mbps throughput.

For more deeper understanding of wifi throughput i would recommend you watching this video and the reading to background pdf:

 http://www.wlanpros.com/wi-fi-stress-test-a-vendor-independent-access-point-analysis/

Still waiting for the second round of the wifi stress including the extreme wireless access points.
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wyfy

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Hi 
is there way to know adapter support 2x2 MIMO ,or 1x1 . Normally vendors does not include it in their datasheet . 
And if you see other vendors test result (iperf ) they are using tcp and published result is  same like 150 when the phy rate is 300 Mbps
Thanks
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If the client is connected to the AP/controller you'd look into the GUI > Report > Clients.
The column Avg. Rate Sent/Rec gives a small clue what the client is capable off.

-Ron
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Looks fine to me...
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Daniel Flouret, Employee

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Laura,

Hope this helps

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Ryan Mathews, Alum

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Good reference
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Ryan Mathews, Alum

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Great....welcome to the Hub.  We're very glad you joined us!
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wyfy

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Hi,

In middleeast and asia

how is the non-dfs channel allocated ? 

Can we use dfs and non dfschannel together ?

Thank you