How Many Devices Can My Access Point Support?
I am going to make an assumption; you receive this question all the time or you’re about to ask it.
Doesn’t it sound fantastic when the answer to this question is above your wildest expectation? ‘How many devices can your AP support at once?’ asked Mr Consumer. ‘400’ replied Mr Vendor. Wow… 400! Ok… now I am going to explain why there is no arbitrary numerical answer to this question and anyone who gives you one either doesn’t understand Wi-Fi or is trying to avoid the following discussion!
How would I answer this question? Well, if you want a real answer I am going to ask YOU some counter-questions:
- What is the Access Point?
- What features will be running on the Access Point?
- What end-user clients(s) will be used?
- What applications will be running on the clients?
Let’s examine these points in more detail.
1. What is the Access Point?
The first and most obvious item is the Access Point itself. Your wireless clients will be connecting to this device and they will be passing traffic through it. It’s ability to support clients depends on a multitude of factors; chipset, memory, CPU, radios, software etc. For example, an AP with a faster CPU will process data quicker than one with a slower CPU which may result in its ability to handle more simultaneous clients.
Additionally, if an AP has a single 2.4GHz radio, the chipset running that radio may support up to 100 simultaneous connections. Compare that to a dual band AP; one radio on 2.4GHz and one on 5GHz. Now we can support up to 200 simultaneous connections, 100 on each radio!
‘Wait a minute!’ I hear you exclaim, ‘You said you cannot assign an arbitrary number, so what is 100 and 200?’ Well spotted. These numbers, like many published in technical documents or presented by vendors are usually limitations imposed by chipset manufactures. To be clear, these are absolute limitations – don’t take these numbers too seriously, why?
Let me pose an analogy; whilst driving you encounter a declining road only requiring you to occasionally press the accelerator. Your car reads 80-90MPG. So… your car is capable of 90MPG? Not so fast! Like access points, cars are capable of achieving great numbers but only in very special circumstances. This is exactly why car manufactures publish multiple MPG figures: Urban, Extra Urban and Combined. Even then, your MPG estimates would be conservative and you may expect something different.
As with MPG figures, there are numerous factors which pick away at the limits, some of which I will cover next.
- Manufactures often use similar chipsets produced by the same manufacture(s) so an AP may be different in design but it will still be restricted by the association limit imposed by the chipset manufacture.
- 802.11 frame specification defines a limitation of 2007 per BSS within the AID field
2. What features will be running on the Access Point?
The second question will vary greatly depending on your chosen vendor. Some vendors have more features than others and some features require more horsepower to run. Example; if the AP is capable of acting as a router, enabling this L3 functionality adds extra processing, inevitably reducing the device’s ability to cope with additional connections. Just remember, everything you enable and every box you check requires the AP brain to work harder, reducing the availability of it’s hardware resources.
Additionally, the simultaneous association limit imposed by chipset manufactures as discussed in the first point can vary somewhat based on the encryption method used. For example, using AES encryption vs. no encryption (open network) will require more processing and airtime. This leaves less resources to serve clients and as a result, less clients can connect. Despite this caveat, do not use anything less than AES encryption with WPA2 unless absolutely necessary!
3. What end-user client(s) will be used?
Moving away from the AP, the end-user clients also have an impact. For example, you have 40 1x1:1 802.11n iPhones capable of drawing 150Mbps or 40 3x3:3 high end 802.11ac devices drawing 1.3Gbps. Which devices do you think are going to demand more resource allocation from the AP? Why, the more capable devices! (If these figures mean nothing to you, fear not! All you need to know is that bigger numbers equate to more potential throughput).
Additionally, newer/more powerful clients may allow for extra functionality. As an example, most smartphones are not capable of streaming a 4K video. A Laptop on the other hand may be able to. This leads me onto the effect of applications…
4. What applications will be running on your clients?
Let me paint you a picture; scenario one - 40 laptops connected to one AP. Scenario two – 40 laptops connected to one AP. Wait, that’s the same thing? It is, except with scenario one the laptops are only accessing email. With scenario two, the laptops are all streaming high definition video from YouTube. Can you see where I am going with this? Yup! Those 40 devices streaming video are going to demand more bandwidth and more processing power from our access points.
It is reasonable to assume then, I will be able to connect more clients to my AP performing basic tasks including email and web surfing compared to resource-intensive clients that want to stream video, download files etc. (less data is being transmitted/received through the AP).
Another consideration is Quality of Experience (QoE). This is the perceived quality that a user experiences when using a service. You may be able to squeeze 50 simultaneous clients onto your access points making VoIP calls, but what about the quality of those calls?
A noteworthy mention is that some manufactures/vendors impose different limits despite using similar hardware. This is sometimes in an attempt to enforce a certain degree of QoE. It is important to realise the quality over quantity consideration.
Ok, let’s bring this all together. The question: What is the simultaneous connection limit of an access point? By now you probably realise this is the wrong question to ask. Your first question should be ‘What is the imposed chipset limitation of your AP for simultaneous clients?’ This will give an indication of hardware/software limitations.
From here, assess the specifications of the access point. Is it a new 3x3:3 802.11ac AP or an older 2x2:2 802.11n AP? The chipsets for both may support 200 simultaneous connections but the 802.11ac AP will support more data passing through it. Most likely, it will also be loaded with newer hardware capable of running additional features and processing more information.
If you need this question answering the best thing to do is test the AP with the devices and applications you intend to use, first hand. I would like to give a shout out to my colleague who wrote an excellent article on the importance of WLAN preparation and site surveys.
It can be tempting to opt for a solution where the response is a quick and simple ‘400!’, especially if the number provided is bigger than the competition. Having read this article however, you should now be wise as to why ‘400’ (or any other number!) is the wrong response (without justification of the aforementioned points). Have a conversation. Work out the details. Gather requirements. Discuss QoE. Conduct a site survey (you may not even care about capacity and instead be concerned with coverage!).All Posts In This Series: