It’s 2021 and you probably have several Wi-Fi deployments lined up. Every organization expects access to Wi-Fi at all times, but delivering a powerful and secure solution is easier said than done. One of the last things any Wi-Fi integrator needs when climbing ladders to set up new access points for a customer, is well… climbing ladders again to replace it with another solution, only to find out that even with the more expensive reputable access points, end users still complain that the Wi-Fi sucks!
Here are the four most common Wi-Fi mistakes that people make when deploying their WLAN:
- Maximum transmission power on all access points (AP)
- Channels overlapping or using the same channel on multiple APs in same area
- Ignoring the Rule of 10s and 3s
- Using very wide channels (80 MHz/160MHz) and too many clients
Let’s dive into each one:
1. Having the maximum transmission power on all APs.
This is the equivalent of walking near a bar and hearing from a block away what song is being played at the highest volume. While this is a good idea to get people to locate the bar and attract the last-minute night-dweller, I hope you will agree that this is not a good idea for regular businesses. While one can understand the convenience of having Wi-Fi access outside the building near the entrances, often you find that signal can be easily be picked up a block away, or at the opposite end of the parking lot with your phone since 2.4 GHz has a good range.
One can imagine the reasons behind this. Most APs, especially the ones from the consumer market, or managed by a local controller, are often blind and do not know if they will be deployed alone or as part of a set, and the manufacturer does not know how far they will be from their users. So, the AP boots, listens for available channels, checks for the local country settings for transmission power and channel use regulations and blasts at max authorized power for a better first user experience. That’s fair, from the manufacturer’s point of view. Imagine if you purchased an AP for a customer and found out after powering and plugging it into the network that you can only get a fair signal, when you are standing right next to it…
Why is this a bad idea to leave the default or crank up the transmission power on all APs to solve Wi-Fi problems? First, with 2.4 GHz you are making it difficult to reuse non overlapping channels in your customer’s environment. Imagine in a floor with four Aps, each of them using channel 1, 6, and 11, while the fourth one is using channel 1 again. If the first and the fourth AP are too close to each other, they will step on each other’s feet and cause co-channel interference, giving way to badfi.
Second, you are simply baiting the bad guys with your simple, short pre-shared key or worse, the open guest SSID. And if you do not think you should worry about bad guys, you are likely having a few more clients from the public using your guest Wi-Fi bandwidth to surf the web freely.
Third, you will likely come across that oh-so-annoying and elusive problem where users report that they apparently have a full signal on their devices but a very poor Wi-Fi experience and are quick to blame the AP. The reason for this behaviour is that while the AP is busy talking to the far away client (struggling to get its frames across a vast space, after all it’s likely a single stream device) all other nearby associated clients to the same AP must wait their turn. Even with MU-MIMO capabilities you would get the same symptoms, because of the laws of physics stating that only when the AP transmits, it will have to be at the same modulation and speeds on all antennas to their clients at any given time. Simply imagine an amphitheatre at a university campus where a distant student directs a question to the professor and can barely be heard by the latter. They would likely have to slow down, ask them to repeat, clarify and then doublecheck if the question is correct and respond back. You can imagine how the rest of the crowd, especially in the front rows, can become annoyed by this (this is why the best venues have microphones ready for the crowd).
What should we do? Ask yourself: Do we really need Wi-Fi signal in the whole parking lot, or just near the entrances? If you place the AP near the perimeter of the company building, see if the radiation pattern of the antennas can be pointed inwards instead. Turn the transmission power down a few notches to cover the areas you need. That means you need to simulate propagation of the signal with professional software or go on-site and measure the RSSI on your phone, laptop, etc, and adjust the values accordingly.
2. Channels overlapping or using the same channel on multiple APs in same area.
This is the equivalent of being at a busy dinner party and you are trying to follow three conversations at the same time. Our brains do not have an optimal amount of focus and while we still engage in a busy environment, talk slower and probably get prompts to repeat, etc. Well, it’s the same for Wi-Fi clients. Since the airspace can only have one AP and client station talking at the time in a same location on a given channel, you end up likely with lots of interruptions and retransmissions.
Why is this happening so often? One can imagine that to eliminate costs, the company decides to skip site surveys and bet on manufacturers’ automatic selection features to figure out what channels and transmission power to use at a given location. If the APs are managed without a controller, you can understand that each device needs to be configured individually which is very time consuming… While Wi-Fi Remote Monitoring and Management (RMM) can help setting this up, you have to set your expectations to a reasonable level since every vendor uses its own method and no one does it perfectly. It can take a long time to find the best adjustments depending on the locations and the number of APs; this can take a few hours or days, if you are doing this in a public environment, competing with many external neighbouring APs popping in and out of your airspace.
What can we do about this? While anyone can get an AP to run, complete a wizard, and broadcast an SSID; it’s another thing to have a plan of action for multiple APs, detailing which area each of them should be covering, gently overlapping to allow roaming, and allocating a non-overlapping channel to each one. In other words, you should do at least a predictive site survey where you pin down where the APs should be placed, and which channels they will use. Then you only need to manually adjust the transmission power of each AP. This can be nailed down much more accurately once you set up an on-site survey and see where the clients are located, and how much signal decay you get from the surrounding obstacles, such as walls, cubicles, doors, columns, etc. The orientation of the AP or external antennas can simply be re-directed inwards, to avoid over spilling to the street or the neighbouring building. And of course, turn it down a few notches! What I mean is lower the transmission power of those AP at the perimeter from 3 to 10 dBm lower can go a long way. Which leads me to my next top mistake.
3. Ignoring the Rule of 10s and 3s
Every time I train on Secure Wi-Fi, I start by giving a quick twenty-minute recap on Wi-Fi fundamentals. At some point in the recap, I will ask the participants if ANYONE has heard the Rule of 10s and 3s. EVERY single time all I get is silence and shaking heads. I also remember when I was a young support rep and was troubleshooting issues with poor Wi-Fi performance, I would look and with the choices given by the UI controlling the access point I could only leverage a few things: The channel and width used (20 or 40 MHz at the time), the security settings for association (WPA2, WEP, Open) and the Transmission power. And when altering the channel or downgrading the security settings didn’t help, I would certainly boost the transmission power in the hope to make the signal louder and hence clearer for the clients to hear the signal. I remember this being for me like a volume radio knob that would gradually make things better. Except that it’s not always helping and in fact, may make things worse for clients hearing that signal further away.
As you may know, wireless communications use radio waves, which is a kind of light, and is measured in watts, a unit of energy. Therefore, the variations of energy are expressed on an exponential scale and measured in decibel-milliwatts (dBm). Letting this much radio energy pass through our bodies is not good for our health, and, although it varies by country, safety regulations worldwide allow the maximum transmission power on an AP to be between 20 and 30 dBm.
Adding or removing 10 dB will respectively increase or decrease the amount of power output by 10 times. With a power increase, the clients will get a better signal from the access point and get better throughput as a result. Also, adding or subtracting 3dB will multiply or divide the power by 2 (of course). Why should we care? If you ignore this rule, you may be designing your Wi-Fi deployment unscientifically, and may get inconsistent results and when you get a customer asking you to look at Wi-Fi performance issues. You may be tempted to simply crank up the transmission power in large increments leading to anything from co-channel interference, exposing your signal well beyond the required location, or interfering with other wireless devices (e.g. medical, industrial, neighbours, etc.). In the most cases, you will likely mess up the roaming experience and have clients switching AP on a seemingly random basis, or worse, for legacy clients; they may become sticky when far away, slowing the experience for anyone else using that same AP.
How to incorporate this simple beautiful piece of theory? Ideally, you have run a site survey where you have measured the attenuation of the obstacles in the location. For example, if you decide to have an AP on in the middle of the ceiling surrounded by offices using glass, you should measure with a client how much perceived signal you get outside the glass wall, and right inside it.
If you notice -3 dB (typical for glass or drywall) RSSI from -65dBmW outside to -68dBmW inside, then you can expect lower throughput in those offices with mediocre or poor quality in streaming… (remember video conference is big these days.). Another detail is that the RSSI is a perceived value, and environment factors make those values fluctuate. A handheld device will have more trouble talking back to the AP (like the Monty Python Holy Grail scene of the Round Table Knights talking to God far in the sky; God has a powerful voice that reaches them easily, versus King Arthur’s voice that can barely be heard). So, in this case, the measurements may indicate that the transmission power must be set 3 to 5 dB louder or require you to place two or more APs to cover the area adequately with lower transmission power. I often use the metaphor of light bulbs; should I use a big spotlight to light up this area, or should I go for a smoother approach and place smaller light bulbs with focused beams where I need them?
4. Using very wide channels (80MHz-160MHz) and too many clients
So that’s it! You read all the theorical specifications about 802.11ac Wave2 / ax Wave 1 (2) and read all the reviews raving with the promising gigabit throughput performance that will spare clients from ever using LAN cables again. Except that like we pointed before, this is a standard mostly driven for the consumer market. Indeed, the only way a client could potentially come near to the promised speeds, would be a single client, with three or four streams, using 5 GHz band within a close range and having a fibre connection all for itself… Does that resemble a home video game console to anyone? But bench marking from professionals point to less than half those Gigabit speeds. Now compare that to most corporate and professional scenarios: mild to high density of clients connecting to the same AP, disparity of clients (stations) ranging from smartphones, tablets, laptops and IoT, all with a variety or ranges and roaming, and not needing to have HD streaming. Even if they were needing that amount of data per client, don’t you think their current infrastructure would be their bottleneck? And we are talking not only of the upgrade of those nodes, but also to implement link aggregation or deploy 2.5/5/10 Gbps ethernet equipment. So, getting hyped up about multi-gigabit throughput while routers, switches and service providers are still bound to single gigabit speeds is a tad premature if one has not tackled that investment first.
In fact, professionals agree that a well-configured wireless network performs way better using 5GHz with 20MHz wide channels, even using low-end APs with 802.11n than going for fewer and newer APs using 802.11ac with 40 or 80 MHz wide channels.
But why are wide channels often slower in professional environments? The reason again, is co-channel interference. Have you noticed how dogs are much more startled when they hear a noise and then try to sleep? They hear a wider frequency and hear more stuff than we do. Similarly, APs using wider channels, get interrupted way more often and therefore are not very efficient for many clients.
What should we do instead? As implied, you should maybe stick to low and mid-range APs that simply do 802.11n and plan to have a few more of them in production but with 20 MHz channels on 5 GHz. Yes, that means more APs to install. But you are more likely to get things right than spending it on fancy upper-range models for features that will not likely be used efficiently anytime soon (client support is usually lacking or delayed).
There are still a lot of administrators relying solely on the AP and the controller to do their magic and instead of testing or validating things, they move on to the next install. While Wi-Fi is indeed one of the most difficult protocols to grasp and troubleshoot, you do not need to know EVERYTHING to deploy Wi-Fi. However, I would like to think that if we could avoid the most common traps, we could push back a little more, to gain necessary information and include that in out predictive surveys. This would mean that our post-installation fine-tuning would feel less frustrating and give us a greater sense of fulfilment, because we would be delivering what we promised as technicians and helping our customers to reach their goals.
For more tips from wireless professionals see the links below. They are simple to follow, fun to watch and a goldmine of good practices about that complex world of implementing Wi-Fi:
Proper Enterprise Wi-Fi Channel Sizing, 9 min WLPC talk
Wi-Fi The Wrong Way, 12 min WLPC talk
Wi-Fi Network Design for Dummies, 1h Ekahau webinar
Wi-Fi Planning, The 7 secrets. 1h Ekahau webinar.
7 Myths of 802.11ac , 1h iBwave webinar
Planning and Surveying Good Wireless LANs with Mr “Bad-Fi”, 1h24m Ekahau Webinar
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