AIrCube Part 2

Part 1 of our AirCube article can be found here

One of the best features about the new aircube is the interface.  On Facebook and other places the aircube has been criticized for it’s lack of features. I believe this is where the simple interface really makes the unit shine.   One thing many people don’t realize is your typical home router really doesn’t have a true firewall. Most routers have features that are firewall like. Most “firewalls” are security by obscurity.  The ability to close off ports is a by-product of a nat router.

Setup was very easy.  I downloaded the ap, scanned the QR code, and then went into the phones wifi and connected to the AirCube wifi. Once I plugged it into my home router I was online.

One of the first things I always do when testing a new device is upgrade the firmware, unless I have a specific firmware version for whatever reason.  Upgrading the firmware on the unit was very easy.  I like the fact you can see the changelog notes with a single click.

Once upgraded the simplicity of the setup really shines through.  By default, the AirCube is in an access point mode. This is probably the default mode which will be the most beneficial for the ISPs out there.  I will explain why in a little bit.

The interface speaks for itself, I could go through screen by screen and spoon feed you the very simple setup screens, but you would get bored very quickly.  It is truly a very minimalist product and interface.

One of the coolest features I like about this product is the scan feature.  For some reason the way it is presented on screen resonates with me.  It makes seeing the frequencies in use handy.  While not a chart or graph, it still accomplishes the same function.

I know this little product has received some ripping from operators on various groups and forums.  However, I think it fills a very basic need.  That need is an easy to configure device which allows devices to access the Internet.  Nat firewalls can be done by the provider, and the user never has to touch them.  This is a trend many operators are headed toward anyway.  Let the provider manage the endpoint for the customer. The customer ends up calling the ISP to do port forwarding or if they have a virus anyway.  If the customer wants to add things in the house, it should be simple, and not add extra layers of NAT and firewall rules.  This is a perfect fit for the Cube.  So don’t dismiss it because it doesn’t have all the fancy features some router have.  Save that for other product lines that you, as the ISP, can manage.


Capacity of a UBNT AP vs the number of clients

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.

Some things that we will assume.
1.You are calculating on an 802.11N Ap with some kind of polling (TDMA, NSTREME, AIRMAX, etc)
2.You know the MCS values and/or data rates at channel widths.
3.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.

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.

So now, on to what affects the total capacity of an AP.

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.
2.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.
3.Plain old signal. Things such as trees, distance, fresnel zone, and antenna gain all affect signal
4.The speed you are giving to each customer.
5.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.

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.

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.

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:
130 / 2 = 65 Megs of Capacity to sell on the AP.
Now here comes the overselling part.
If we oversell at a 2:1 ratio we have 130 Megs of capacity on the AP.
If we oversell at a 3:1 ratio we have 195 megs of capacity on the AP.

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.

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.

Now to the real world (aka why do my customers hate me and my AP sucks?).

The following is a real AP in the wild.  Blacked out to protect the innocent from script kiddies.

Couple of things to Note (circled in Red).

20 MHZ Channel
Capacity at 45% . This is more important than anything, even CCQ.
43 clients associated.

Let’s apply our math we learned earlier. We know a 20 mhz channel nets us MCS15 – 130 Megs

Here is the kicker.  Our capacity is at 45%.  This means we only have 45% of 130 megs of Over the air capacity.  Take this in half (130 / 2= 65   45% of 65 = 29.25.
This means all 43 of these customers are sharing 29 megs of capacity on the AP.  And the quality isn’t the greatest (37%).  So 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.  It is important to note I am talking about the quality and capacity of the signals, not signal strengths.

If those 43 people are all paying for, let’s say, 2 Megs download.  That means your AP needs to support a minimum of 86 megs. Thats without overselling.  We only have 29 megs in the current state!

We need to get those capacity numbers up.  How do we do that?

1. Channel selection. A noisy channel will drag everyone down.

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

3. Shielding. This helps eliminate the amount of stuff a client or AP hears.

4. Channel Width.  Sometimes dropping the channel width down can increase signals, thus raising the overall capacity.  Keep in mind it will lessen the overall capacity of the AP.

5.Simply getting rid of customers that shouldn’t be installed.  We have all done installs that were iffy.  These can drag down the overall capacity.

I hope this has helped understand.  The 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.