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802.11ac only


How do I make the Access Point only support 802.11ac or 802.11n. Is there a way to only support certain protocols without allowing things like 802.11a and 802.11b?

The only thing I see if what I provide. I don't see an "n-only" or an "n and ac" selection.
ap7532-85ACFC(XXX)#data-rates 5GHz

a-only an default custom

ap7532-85ACFC(XXX)#data-rates 2.4GHz

b-only bg bgn default g-only gn custom

12 replies

Userlevel 3
802.11n and 802.11ac are actually collections of various different mcs rates.
If you select custom, you can then specify which MCS rates exactly you want to support.
If you type ? at the end of the data-rates CLI you'll see a list of what's supported.

This chart explains the different MCS rates in general.
https://www.wlanpros.com/mcs-index-802-11n-802-11ac-chart-3/
Userlevel 2
Using the chart that Andrew provided you can select the specific n or ac rates. Custom data rates can be configured on both the WLAN itself or on the radio interface. It is suggested to configure data rates on the WLAN.
Userlevel 3
Hello Mark,

Data rates can be configured on the radio or wlan. As Andrew mentioned, you can select custom data rates and allow certain data rates only, if you so choose.
Right, but the problem is I cannot just support 802.11n and AC. I have to support more than that.

MCS-4s is 802.11a/g and only part of 802.11ac. How would I just support all of 802.11n and AC?

MSC0-7 is everything. I am not clear how do just support the protocol that I want. Looking at that chart, I have the same question. So is the answer that I cannot support just 802.11n and AC. I have to support more than this?

ap7532-15E560(config-device-84-24-8D-15-E5-60-if-radio1)#data-rates
a-only an b-only bg bgn custom default g-only
gn mcs
ap7532-15E560(config-device-84-24-8D-15-E5-60-if-radio1)#data-rates custom
1 11 12 18 2
24 36 48 5.5 54
6 9 basic-1 basic-11 basic-12
basic-18 basic-2 basic-24 basic-36 basic-48
basic-5.5 basic-54 basic-6 basic-9 basic-mcs0-7
mcs-1s mcs-2s mcs-3s mcs-4s mcs0-15
mcs0-23 mcs0-31 mcs0-7 mcs16-23 mcs16-31
mcs24-31 mcs8-15 mcs8-23 mcs8-31 basic-mcs-1s
ap7532-15E560(config-device-84-24-8D-15-E5-60-if-radio1)#data-rates custom
Userlevel 4
You mean you only want MCS rates? I wouldn't recommend that. Not all clients like connecting using MCS rates. You will need some of the basic OFDM rates.
So - choose custom rates and choose what you need. This is not protocol issue. Protocol defines higher rates but for the most part in real world with variety of clients - you need to choose your rates based on your deployement, AP spread and overlap and clients that you have.
Userlevel 4
Based on the wireless standards it's not possible to disable 802.11g or 802.11a data rates. You still need this basic rates. 802.11n and 802.11ac are no possible basic rates.

Why you would disable the 802.11g data rates?
Userlevel 1
I Thought that AC would be better for use in a wifi bridge,
Userlevel 4
You will use it for a bridge or mesh? The mesh link select the best rate. Just disable the low basic rates. This are used for broadcast and multicast.
So I am still not clear if I can only support 802.11n and AC only, I am going to say the answer is no. I don't want to support 802.11b clients, they are two slow and not wanted on my network, so I will not allow them to connect. The same is true of 802.11a and 802.11g clients, but if I have to allow them, then I will. So if I want 802.11n and AC only, what do I pick?
So I am still not clear if I can only support 802.11n and AC only, I am going to say the answer is no. I don't want to support 802.11b clients, they are two slow and not wanted on my network, so I will not allow them to connect. The same is true of 802.11a and 802.11g clients, but if I have to allow them, then I will. So if I want 802.11n and AC only, what do I pick?
Userlevel 3
Hi Mark,

The comments above are spot-on. There are two data-rates at play in a Wi-Fi network, the multicast rate used as the network's lowest common rate, which is generally what clients connect on before negotiating up to a higher rate (as well as other network activities) and then the PHY rate associated client(s) use for passing traffic. Having the multicast rate set at 24 or 36Mbps (.11a/g OFDM rates) provides the best performance gain.

As you say; preventing 802.11b clients from associating is a must to optimise speed on your network as these clients take up so much air-time they slow the rest of the network down. Although mechanisms such as 'airtime fairness' help to minimise the .11b-client impact issue.

Please bear in mind that just because you have low data rates available on your network, doesn't mean clients will utilise them. Your Wi-Fi design and configuration should minimise signal bleed to prevent clients connecting at long distances and therefore at lower PHY data rates. Wi-Fi needs the lower data rates to maintain connectivity in the case of high-levels of interference and other degrading factors.

I would say that having some .11a/g (OFDM) clients on your network running a data rate of at least 24 or 36Mbps will not have a noticeably negative impact on your Wi-Fi network's performance.

I hope that helps,
Darrel.
Ok, so I have to support a basic rate of some kind. I think I am following. So if I want to limit 802.11a and 802.11g usage on my network.

I would set the following:
ap7532-15E560(config-device-84-24-8D-15-E5-60-if-radio1)#data-rates custom basic-36 mcs-1s mcs-2s mcs-3s

This would limit 802.11g to only use 36Mbps and would allow all of the n and ac range.

ap7532-15E560(config-device-84-24-8D-15-E5-60-if-radio2)#data-rates custom basic-36 mcs-1s mcs-2s mcs-3s

This would limit 802.11a to only use 36Mbps and would allow all of the n and ac range.

Is this a correct statement?

In addition, do I have to support basic-24/36, or can I just support basic-54? Is there a reason you picked 24 and 36, rather than 54? Just wondering.
Userlevel 3
Let me try to clarify...
The link I had provided initially is probably not appropriate as it covers speeds at various signal levels and not the details how each speed works.
This may be a better resource: http://mcsindex.com/

While they may appear similar on the surface. MCS rates are not 802.11a/b/g rates.
For instance, even at MCS0, the slowest rate, the speed is 6.5MBps or 7.2MBps, depending on guard-interval, which is already a bit faster than slowest rate of 802.11a or g. It also does not use the same modulation schemes as 802.11a/g (OFDM), or 802.11b (DSSS). So legacy clients wouldn't be able to connect since they wouldn't understand what's being said over the air, BUT as others have pointed out, as per the spec, you cannot completely disable OFDM data rates. For instance setting "data-rates custom basic-mcs-1s" produces a result of basic 6 and 6 + mcs-1s as supported rates. An alternative might be to specify "data-rates custom basic-36 48 54 mcs-1s mcs-2s mcs-3s". So at least your slowest speed would be 36Mbps if a 802.11a/g client were to be attempting any sort of connectivity.
You can use "show wireless radio detail" to see what actual rates end up being selected based on your configuration.

As Timo pointed out, you should also take into consideration broadcast and multicast traffic. By default these will be sent at the highest "basic" rate. So in the above example, this means all broadcast/multicast traffic will go out at 36Mbps. Obviously broadcast traffic being sent at 36Mbps is going to take more air-time, and air-time is actually the most precious resource in a WiFi network.
You can tell the AP to use dynamic rate selection among the supported rates when transmitting broadcast/multicast with the non-unicast tx-rate CLI command (use ? to see list of options).
In a MESH scenario there is no reason why you'd need the broadcast/multicast running any slower than normal traffic, so non-unicast tx-rate dynamic-all might be a more appropriate selection.

If you want to drill down further, the client probe requests/responses typically are also sent at very low speeds, this can also take up a lot of air-time. You can control at what speed the probe responses will be sent with the probe-response rate CLI command, but you can't easily control what the clients are doing.

Lastly, while there are many "knobs" available to tweak the operation of the radio / wlan, casual tweaking can lead to some pretty terrible results.

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