Wireless Access

Occasional Contributor I

Are there minimum required rates for 802.11n and 802.11ac?



I would like to know if there is a Minimum requirement for N and AC as far as transmit rates are concerned.  I had heard that there is a requirement of 6 and 24 being active for N to work properly, but I couldn't find anything Aruba related to support that. 


I am investigating trasmit rate limitations to facilitate better overall network performance in high capacity situations.  We frequently have over 1000 users in a relatively small location, and this has be creating difficulties for throughput, in particular on G Band devices.  


Upon doing several tests using a spectrum analyser, I noticed that in particular, where we have an SSID that has limited internet speed (of 10megs), having higher transmit rates was actually creating a severe problem, as the client was staying in the air for a long period of time due to limited internet speeds with increased utilization observed on the spectrum analyser to 80-90% using just one device (on G) for so long as I was doing the test.  Meaning that in the air, I was seeing the full rate being used, not just 10megs, despite my speed to the internet being limited. 


This got me thinking, that where the internet speed can not match the transmit rates, it is likely better to lower the transmit rate as much as possible to match the maximum speed available via the internet where there is no intranet in use.  As we have a throttle for clients of a maximum internet speed of 10megs, I'd like to know if for example, there would be any issue in setting the maximum transmit rate to 12 for this particular SSID or if this would cause connectivity stability issues with N devices.   It is used for internet purposes only, and does not allow for any internal communication. 


I have tested this with over 1000 users on site with 6 and 24 rates enabled, and have seen a significant improvement in over all capacity, where we would frequently see utilization on high traffic AP's sitting around 80-90%, with the rates lowered, this very rarely occured, and generally speaking utilization never went over 60%, and on far fewer AP's and suspect that in the case where internet is limited to 10megs, being able to lower the rate even further would likely increase performance even further. 


Thank you. 

Guru Elite

Re: Are there minimum required rates for 802.11n and 802.11ac?

Where did you hear that requirement?


You probably need to enable the 54 rate at minimum.  It is hit or miss whether or not clients will associate having only that rate enabled.

*Answers and views expressed by me on this forum are my own and not necessarily the position of Aruba Networks or Hewlett Packard Enterprise.*
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Occasional Contributor I

Re: Are there minimum required rates for 802.11n and 802.11ac?



I set up a test environment this morning - and at least with the 4 devices I used to connect with, everything worked with using just a trasmit rate of 6.  (The minimum requirement for G,A)


All devices connected via the N or AC and in status, every device connected with a speed of 54Mps or higher according to the device status.  (Android Phone, older Netbook with G,N, Newer Laptop with a Intel 7260, Older Laptop with a dlink built G,N).


I'm not entirely certain how the transmit rates work, with the transmit rate set to 6 on an unthrottled VLAN/SSID, I still connected at 54Mps or higher speeds, however when doing a practical speed test, with the transmit rate set to 6, my download/upload speeds were capped on each device to approximately 11megs up and down.  With the transmit rate set to 54, download speeds on the N,AC devices capped out at speeds of near 150meg up and down close to the available max available bandwidth for the internet connection.


So for my purposes, it looks like the transmit rate of 6 will work for the SSID where the VLAN is throttled to 10meg per user (throttling is not at the controller, but at a separate gateway/portal device), matching transmits in the air to the available internet speed per user out the gateway.


I'd love to see this concept officially explored - all best practices/guides state its best to maximize the rates to achieve quicker off-loading times - however, I've never seen any paper that addresses throttled internet connectivity, or even just a slower pipe, and it's impact on utilization in N,AC environments where the trasmit rates are far higher than the available internet speeds.



Guru Elite

Re: Are there minimum required rates for 802.11n and 802.11ac?

Have you seen the VHD validated reference design?




| Tim Cappalli | Aruba Security | @timcappalli | timcappalli.me |

NOTE: Answers and views expressed by me on this forum are my own and not necessarily the position of Aruba or Hewlett Packard Enterprise.
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