Ruckus AP capacity planning/formula

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Ok,

CLIENTS: Single stream, 802.11ac

Connected to 5Ghz (only) and 20 channel width with theoretical and optimal RF conditions

AP: Single R500

How many concurrent clients can I serve with for example a Netflix 5mbps stream?

What is the formula / model?
Thanks
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Samuel Eng

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Posted 2 years ago

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Sean

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Example:

If your AP has a max TCP throughput of 40Mbps when using a 20MHz channel, this would put the AP at 100% of its airtime utilisation when the AP was passing 40Mbps.

To ensure that you dont overload your AP's, it is always best to work to capping the limits within your design to be using 75% of the AP's airtime utilisation.

This being the case your max TCP throughput value you should be aiming at the AP consuming is 30Mbps.

The simple math now is that if you divide 30 by 5 you get 6 clients.

Note: In this example this would mean that each client would need to be drawing a constant value of 5Mbps.

Now all you need to do is find out what the max TCP value is of a r500 when uising a 20MHz channel using a single stream - you can do this by conducting a FTP or iperf test.

Note: you will need to use more than 1 client to consume all of the available bandwidth and graph the network interface of the FTP/iperf server (I would use a linux machine for this as its more accurate)

I hope this answers you question.

Good Luck
(Edited)
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Bill Burns, AlphaDog

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The short answer is "maybe 25" if you allow both bands to be used simultaneously.
(which is not the use case you described)

Keep reading if you want more detail.

I don't know what the "official" answer to this question is but since you're looking for a theoretical (pie in the sky) number:

I'd look at the info Ruckus provides for the AP:
http://www.ruckuswireless.com/products/access-points/zoneflex-indoor/zoneflex-r500

...ignore the 5Ghz max theoretical bandwidth (since you're specifying 20Mhz channelization) and substitute the 2.4Ghz figure of 300Mbps, divide by the 5mbps you specified, and arrive at a figure of 60 clients.

I would never expect to get close to "theoretical and optimal" performance, but since I'd configure my APs to support 40Mhz channelization (or more w/ ac support) and I'd expect some number of clients to support higher channelization and netflix should provide enough caching to smooth over momentary congestion issues...
Well... You're still not going to get close to that theoretical number.

BTW:
WiFi might not be your only bottleneck.
Do you have 300Mbps of internet connectivity?


Here are independent throughput results found on the Ruckus website:
http://www.ruckuswireless.com/carnet-performance-testing
If I'm reading it right, the effective throughput of an R500 (with 60 clients pulling traffic) drops to 80Mbps, leaving something better than 1Mbps per client.
If we use 80Mbps as our bandwidth cap, you get 16 netflix clients. (at 5Mbps each)
...but the "real world" nature of those results were disputed by other vendors.

Tom's Hardware claimed that a Ruckus ZF7363 delivered 111Mbps to 60 clients.
http://www.ruckuswireless.com/press/releases/20110718-independent-test-reveals-ruckus-outperforms-ot...

A more relevant test was conducted against a ZF7982:
http://www.ruckuswireless.com/press/releases/20130219-ruckus-smart-wi-fi-takes-top-marks-in-non-vend...
Their conclusion was that 25 iPad clients could simultaneously stream "HD" video through a single 7982.

So, compare the advertized performance numbers of a 7982 to those of the R500, scale the results appropriately and... you might get 10 or 12 simultaneous video clients per band.
I'm guessing, 'cause I didn't do the math there.
Plus, we totally lost track of your 20Mhz channelization specification.

The tests that Ruckus is highlighting seem to indicate that other brands would do worse.

..but feel free to search for your own throughput stress tests or conduct your own.
(Edited)
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Samuel Eng

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Thanks for your replies. I use 20Mhz channelization for frequency reuse on the 5Ghz.

Didi I get this right. If I go from 20->40 I can push more data to more clients? Is 20 "limiting" my AP's capacity as a whole?
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John D, AlphaDog

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Quite honestly, I wouldn't prematurely go 20MHz, unless your deployment is really so dense that you've got one AP on each channel from 36 to 161 all within earshot of each other and still need more capacity.

If you go from 20 to 40, you can push a higher bandwidth to each client, which may make them happier in terms of being able to achieve a higher bitrate/throughput at a greater distance, and that would hopefully get them off the channel faster.

I've found that in moderate density, 40MHz is still quite appropriate and even leads to more satisfied users, since they see bigger numbers when running a speed test, and you still get good air efficiency because clients get off the channel faster.
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David Henderson

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We just did some testing of a Ruckus R700 AP. We had 1080p video sitting on an internal server and used new MacBook Pros to connect. These laptops all had 802.11ac nics. We streamed this video to one client and then kept adding clients until we saw pausing or stuttering in the video. This was all using 20Mhz channel width and only 5GHz. Seven clients worked fine, as soon as we added the 8th video stream we got stuttering. Keep in mind that 1080p video is using more bandwidth than youtube videos unless they are HD and full screen If we used both bands I am guessing we could double the number of streams
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Sean

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Please replicate on 2.4Ghz and see what happens and r710 has no airtime fairness.
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David Henderson

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Unfortunately I do not have all the test gear any longer. We borrowed test gear from Aruba and Ruckus and did some extensive internal testing before deciding to go with Ruckus. All the test gear was returned. This summer we will be deploying 400 R710 APs. I hope that airtime fairness is working by then
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John D, AlphaDog

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1080p video is generally defined to be around 8-10mbit bitrate... Getting ~56mbit of video throughput across 7 clients on a 20MHz channel seems like it's not too far fetched. My office uses, let's say, a Ruckus competitor's AP's that they prematurely locked to 20MHz because "high density" and I can barely pull 80mbit from it using a 1 client : 1 AP test.

If it's possible to get more than 7 clients to stream 1080p from a single AP at 20MHz, I'd be highly impressed. But at any rate, this is one of the reasons I was saying earlier that it's probably a mistake to prematurely decide to use 20MHz channels unless it's an extremely dense setup with 12+ overlapping AP's at a given point.
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Sean

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ATF by this summer..... wait for the tumbleweed :)
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David Henderson

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I wanted to followup with some additional testing we did, should have put this in my first post. After we did the video streaming test at 20MHz channel width and got 7 802.11ac laptops streaming 1080p video we did two more tests.

At 40MHz channel width with one AP we got 13 laptops streaming 1080p video

At 20MHz channel width with three APs, we got 18 clients streaming 1080p video. The laptops were evenly distributed with 6 clients per AP
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Bill Burns, AlphaDog

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Short answer:
Go for 40Mhz channelization (at least) in the 5Ghz spectrum.

You generally place APs close enough together to provide good 2.4Ghz coverage.
5Ghz spectrum does not propogate as well and there is more 5Ghz bandwidth available.

If you go for max bandwidth (channelization) on an AC capable AP, you've cut yourself down to 3 usable 5Ghz channels.
That's not any worse than the 2.4Ghz situation and (since 5Ghz signals don't propogate as far) you're still less likely to get interference in the 5Ghz band.
(assuming there are no 5Ghz cordless phones, etc.)

In general, I let the APs choose their channelization, and they go for the max that they're capable of.
I don't have many AC capable APs but so far I don't think this has caused me any problems.
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John D, AlphaDog

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It's said to be 10.0. I have no idea when that will be released.
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Bill Burns, AlphaDog

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I didn't realize that airtime fairness was missing from the R500. (at the current firmware release) This makes it much less suitable for streaming (downloading) video. (on 5Ghz)

Note: AFAIK: Airtime fairness applies to *downloaded* traffic.
All it takes is for one user to *upload* a large file to potentially monopolize "all" the airtime on a given channel.
I have not noticed Rucks (or any vendor) rate limiting client transmissions.

Most traffic is downstream so this usually isn't an issue but every once in a while this can kill WiFi performance.
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Sean

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@ David - I am unsure and we have not yet been given and firm dates towards commital on ATF from Ruckus for the r series AP's.

@ John - I think that might creeeeeeeep a little :)

@ Bill - I thought they normalised across DL and UL in regards to ATF, I cant remember 100% for sure, but I'll find out and let you know.
(Edited)
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John D, AlphaDog

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I thought so too for ATF. I don't know if QoS / heuristics does as well on uploads though or for controlling upload vs download balance.
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Bill Burns, AlphaDog

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It's been a long time since I tested this. (upload ATF) The last time I tried, a single client could monopolize airtime and starve other clients.
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Samuel Eng

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Ok, thanks for your advice. Keep in mind that chaning from 20->40 you lose 6dB per ch width doubling. That's half the distance.

But I can get my head around total AP capacity. Will channel width affect? Total net throughput if you compare 20 to 40?
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Sean

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Lowering the amplitude in a carrier wave would be the loss in transmit energy that the white paper talks about i.e. moving from -72dBm to -75dBm.

Increase in the Noise Floor would be like -97dBm when using 20MHz to -94dBm when using 40MHz.

Interesting paper though and it's spurred me on to do some reading :)
(Edited)
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David Henderson

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So when we do our physical site survey, surveying using a 20MHz channel width or 40MHz channel width should make no difference? In other words, the AP placement and density will the same either way?
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John D, AlphaDog

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No, not entirely true. Roughly speaking, 40MHz channel means each AP delivers twice the bandwidth/throughput as a 20MHz channel width. Of course, in the real world, it's not actually 2x, but it's close. That usually translates to needing half as many AP's, or being able to cover slightly more range. For example, if your goal is 10mbit/s everywhere, you might find that where a 20MHz AP delivers 10mbit, a 40MHz AP delivers 18mbit, so you expand your 10mbit coverage radius by some.


Of course, this all starts to break down if you are in an overlapping coverage radius situation, like a busy stadium / convention center where you really need 12 overlapping AP's or more to cover the same area. Then you might actually run out of 40MHz channels and find it advantageous to use 20MHz channels to increase density.


EDIT: Long story short, it doesn't change the coverage *range*, but it roughly doubles the data rate delivered at each distance. And most of the times when people say range, they really mean range at which the AP can still deliver some threshold data rate, like 5mbps or whatever.
(Edited)
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Sean

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Your density of AP's is always based on application demand and client concurrency.

Lets say you have a auitorium with 100 people.

They all need to have 10Mbps each with no contention.

That means you need 1Gbps of TCP throughput.

The clients are 1:1x1 and dual band capable

The theoretical throughput of the AP is 80Mbps (75% airtime utilisation)  based on the clients capabilities.

This means you need 7 AP's right... wrong.

You clearly not gonna deploy 7 dual band AP's in that area so you need to look at it from a radio basis.

This would mean you need 13 radios of which 4 would be 2.4Ghz (1,5,9 & 13 if your lucky enough to be in the UK) or 3 using channels 1,6 & 11, and the remaining 9 or 10 would be 5GHz.
(Edited)
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John D, AlphaDog

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Right. Sean's scenario above primarily focuses on density of clients being the limiting factor / bottleneck for coverage / AP density.

The other scenario is the lower-density but higher-throughput scenario, which probably also needs to be considered. Especially since David brings up a 1080p video streaming scenario... In that case, another factor is, at what range can the AP deliver a data rate capable of sustaining the required speeds?

What actually brought me to Ruckus is I have special business needs to deliver a minimum of a 100mbit data rate in a 1500 sq ft dwelling. And even though I only have 10 or so possible clients that could need that rate, it took me 2 802.11ac AP's running 80MHz channels to attain my goal in a relatively small area. Of course, now I can probably fit a convention center's people in my house and give them Facebook quality wifi...


The modern classroom setting is probably somewhere between these two extremes.
(Edited)
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Bill Burns, AlphaDog

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Oh... I didn't consider that Samuel might be trying to figure out how many 5Ghz APs he needs to support a certain number of "video" clients.

Samuel:
Are you aware of how many non-overlapping 40Mhz channels there are in the 5Ghz band?
I think it's 12.
https://en.wikipedia.org/wiki/List_of_WLAN_channels

How many clients do you need to support?
Would 12 channels be enough for your application?
(or 15, if you're allowed to use the 3 2.4Ghz 20Mhz channels and consume "all" spectrum for this one purpose)
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John D, AlphaDog

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One other point that came to mind: Don't forget that even if channel width is set to 40MHz, 20MHz rates are still in play. I routinely see my 80MHz capable units actively using 40MHz or 20MHz rates particularly close to the fringe of coverage. But of course, relying on this too much will result in poor spectrum efficiency, if you really are close to saturating all your 5GHz spectrum.