{"id":136,"date":"2014-08-27T05:19:36","date_gmt":"2014-08-27T05:19:36","guid":{"rendered":"http:\/\/www.mtin.net\/blog\/?p=136"},"modified":"2014-08-27T05:22:46","modified_gmt":"2014-08-27T05:22:46","slug":"capacity-of-a-ubnt-ap-vs-the-number-of-clients","status":"publish","type":"post","link":"https:\/\/www.mtin.net\/blog\/capacity-of-a-ubnt-ap-vs-the-number-of-clients\/","title":{"rendered":"Capacity of a UBNT AP vs the number of clients"},"content":{"rendered":"

Almost all the time I get asked: “How many clients can an AP handle?” . My answer is always a very long and drawn out one. There is no set in stone answer. There are many factors which can affect this. I will go into some of these and then explain how to calculate this.<\/p>\n

Some things that we will assume.
\n1.You are calculating on an 802.11N Ap with some kind of polling (TDMA, NSTREME, AIRMAX, etc)
\n2.You know the MCS values and\/or data rates at channel widths.
\n3.When I say in an ideal situation I mean basically in the lab. This is our baseline. This means no outside noise, everything is working properly, and all the connected clients are excellent.<\/p>\n

Before I get into what affects how many clients can an AP handle we need to shift our thinking a little. We don’t think in terms of how many clients can an AP handle. We need to think in terms of how much capacity an AP has. This is very important to think in these terms. If you do so things will become more clear and more quantifiable.<\/p>\n

So now, on to what affects the total capacity of an AP.<\/p>\n

1.The channel width. In and ideal situation you will get more Capacity out of a 20 mhz channel than you will a 10mhz channel.
\n2.Noise. In the real world you will have interference. If you have interference the noise floor drops, customer signals can’t reach maximum modulation, and there are retransmits.
\n3.Plain old signal. Things such as trees, distance, fresnel zone, and antenna gain all affect signal
\n4.The speed you are giving to each customer.
\n5.Overselling. The concept of overselling has been around since the dial-up days. You are betting your customers are not all online at the same exact time doing the exact same stuff. So you can oversell your capacity. I will explain this a little more in a bit how this factors in.<\/p>\n

Okay, so let’s dive into this. I am going to use a Ubiquity Rocket M5 as an example. Again, this can be applied to any polling type N radio.<\/p>\n

Say we have a Rocket M5. At a 20MHZ channel the best modulation this M5 will do is MCS 15 at 130 Megs of over the air. What do you mean Over the Air? Well there is a difference between actual throughput and the Wireless Data Rate (aka over the air). Your actual throughput\/capacity will be 1\/2 of the over the air rate minus a little for overhead. I factor in 10% overhead for easy figuring.<\/p>\n

Back to our figuring. You have 130 megs of capacity on your AP in an ideal situation on a 20 mhz channel. If we do our math:
\n130 \/ 2 = 65 Megs of Capacity to sell on the AP.
\nNow here comes the overselling part.
\nIf we oversell at a 2:1 ratio we have 130 Megs of capacity on the AP.
\nIf we oversell at a 3:1 ratio we have 195 megs of capacity on the AP.<\/p>\n

We can do higher ratios, but it starts to become a moving target. With the spread of Netflix, Youtube, Hulu, and other streaming services the average customer is sucking down more and more bandwidth for longer periods of time. Think of a restaurant with so many tables. If your customers are staying longer and longer, you don’t have as much seating capacity to turn over for new people to sit down and consume your food. This is for another blog post.<\/p>\n

So, let’s say we are overselling at 3:1. We have 195 megs of capacity. We now need to think about what packages we are selling to our customers. If they are all say 5 meg packages, this means we can safely sell 39 connections to the AP. 195 \/ 5 = 39. You can figure up the math if you have 3 Meg, 10 meg, or a mixture.<\/p>\n

Now to the real world (aka why do my customers hate me and my AP sucks?).<\/p>\n

The following is a real AP in the wild. \u00a0Blacked out to protect the innocent from script kiddies.<\/p>\n

\"ubnt-main-screen\"
\n<\/a>Couple of things to Note (circled in Red).<\/p>\n

20 MHZ Channel
\nCapacity at 45% . This is more important than anything, even CCQ.
\n43 clients associated.<\/p>\n

Let’s apply our math we learned earlier. We know a 20 mhz channel nets us MCS15 – 130 Megs<\/p>\n

Here is the kicker. \u00a0Our capacity is at 45%. \u00a0This means we only have 45% of 130 megs of Over the air capacity. \u00a0Take this in half (130 \/ 2= 65 \u00a0 45% of 65 = 29.25.
\nThis means all 43 of these customers are sharing 29 megs of capacity on the AP. \u00a0And the quality isn’t the greatest (37%). \u00a0So this means there are retransmissions going on between the client and the AP. The client can’t talk as fast as it is capable of in most cases. This means you can’t oversell the AP as much due to the quality of the signals being poor. \u00a0It is important to note I am talking about the quality and capacity of the signals, not signal strengths.<\/p>\n

If those 43 people are all paying for, let’s say, 2 Megs download. \u00a0That means your AP needs to support a minimum of 86 megs. Thats without overselling. \u00a0We only have 29 megs in the current state!<\/p>\n

We need to get those capacity numbers up. \u00a0How do we do that?<\/p>\n

1. Channel selection. A noisy channel will drag everyone down.<\/p>\n

2. Antenna gain. \u00a0This can be done at both the client and the AP. \u00a0A higher gain or better quality antenna can cause the clients to “hear” better. \u00a0You might not get an increase in signal strengths, but you are looking for an increase in quality. I use a loudspeaker metaphor. \u00a0You can hear a loudspeaker from a far distance, but you might not always be able to make out what is being said. \u00a0If you can somehow make out what is being said more clearly, then you don’t have to have the speaker turn up the volume.<\/p>\n

3. Shielding. This helps eliminate the amount of stuff a client or AP hears.<\/p>\n

4. Channel Width. \u00a0Sometimes dropping the channel width down can increase signals, thus raising the overall capacity. \u00a0Keep in mind it will lessen the overall capacity of the AP.<\/p>\n

5.Simply getting rid of customers that shouldn’t be installed. \u00a0We have all done installs that were iffy. \u00a0These can drag down the overall capacity.<\/p>\n

I hope this has helped understand. \u00a0The biggest thing I want you all to take away from this is think in terms of the amount of capacity you have to sell, not the number of connections.<\/p>\n

 <\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Almost all the time I get asked: “How many clients can an AP handle?” . My answer is always a very long and drawn out one. There is no set in stone answer. There are many factors which can affect this. I will go into some of these and then explain how to calculate this. 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The last photo is side by side compared to a UBNT M5 Nano","rel":"","context":"In "Bitlomat"","block_context":{"text":"Bitlomat","link":"https:\/\/www.mtin.net\/blog\/category\/bitlomat\/"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/www.mtin.net\/blog\/wp-content\/uploads\/2014\/09\/IMG_2321.jpg?resize=350%2C200","width":350,"height":200},"classes":[]},{"id":220,"url":"https:\/\/www.mtin.net\/blog\/bitlomat-announces-passport\/","url_meta":{"origin":136,"position":1},"title":"Bitlomat announces Passport","author":"j2sw","date":"January 9, 2015","format":false,"excerpt":"From the Bitlomat Page: Bitlomat has developed Passport, an innovative point-to-multipoint TDM-derived protocol with the needs of large scale outdoor networks and wireless internet service providers (WISPs) in mind. 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