Ruckus AP capacity planning/formula

[samuel_eng]

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

[seanmuir]

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 🙂

[david_henderson]

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?

[john_d]

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.

[seanmuir]

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.

[john_d]

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.