CommScope's RUCKUS provides top-of-the-line wireless access points (APs) and network switches to connect them. Over my years visiting customer sites, I’ve found some recurring issues that can lead to these frustrating Wi-Fi fumbles. It turns out you really need two things to have awesome Wi-Fi.
First, you have to start with hardware that’s capable of handling a lot of clients and traffic. Without good hardware, you’ll be fighting an uphill battle to get things working well. The second thing you need—and certainly a less well-known thing—is good network design. A Ferrari needs a racetrack, not a gravel road, to show off what it can do. Design is what determines how much you get out of your hardware. Since it’s fairly straightforward to ensure you’re working with quality enterprise network hardware, let’s focus on the impact of design—and the four most common problems I’ve come across in my field experience.
Reason 1: More access points does not mean better Wi-Fi
Most people think that if the Wi-Fi is not working well, adding more access points (APs) will fix everything. Surprisingly, this is sometimes the worst thing you can do because Wi-Fi is a shared medium. There is only a certain amount of airtime available to send out electromagnetic waves—so adding APs without a smart plan can cause them to interfere with each other and make matters worse, not better.
When multiple APs are on the same channel and interfere with each other, we call that co-channel interference. This scenario is common in places like schools, where each classroom has an AP. In situations where you absolutely must get more APs close together, you may need to lower your channel width. I try to start my channel width for the 5 GHz spectrum at 80 MHz. For a typical phone device, this should yield a connection speed around 800 Mbps.
If our APs are densely installed, we may have to drop that channel width down to 40 MHz, but that also drops our connection speed for a typical phone down to 400 Mbps, which is still a very usable speed. But if you have more than ten APs that can see each other, you will have to drop the channel width down to 20 MHz; and that cuts you connection speed down to around 200 Mbps, still serviceable but at this speed, other factors like overhead and distance away from the AP become more significant considerations.
The best way to fix this frustration is to come up with a proper design. Use WLAN softwares to design and build a predictive survey to help you properly place APs throughout your building. For most schools, I start with one AP for every other classroom alternating across the hall in a zig-zag pattern. Of course, each building is different and needs to be evaluated to get a proper design, but this can be a good starting strategy because it reduces co-channel interference.
Reason 2: You need to separate VLANs
A couple years ago, I went out to help a college with their dorm room Wi-Fi. They told me that when the students were on wired connections, things worked well, but if they tried to use the Wi-Fi, it was a nightmare. After some investigation, I found that the wired and the wireless traffic were on the same virtual LAN (VLAN), and the VLAN had a large subnet with thousands of devices on it.
Wi-Fi is a shared medium. On a wired switch, every port is its own separate collision domain, but on Wi-Fi every AP is a single collision domain, kind of like a network hub. For one device to talk, all the other devices have to stop talking (that is becoming less true with newer Wi-Fi standard, but it’s still good practice to separate things out). By having the wired and the wireless networks on the same VLAN, any device that sent out a broadcast packet would then take up airtime on all the radios, tying up valuable airtime on that shared medium for packets the Wi-Fi clients don’t care about.
To remedy this, I had them make a couple new VLANs and move all the wireless traffic into those VLANs. I had them make sure that there were fewer than 250 devices per Wi-Fi VLAN. This makes it so that any devices that send out broadcast information keep that traffic contained to that smaller VLAN.
Reason 3: MCS rates need adjustment
Wi-Fi must be adaptable for every situation. There are times that an AP can talk to one client nearby, and another client very far away in the next packet. When devices are far away, the AP must use slower data rates to limit data lost in transmission. This is done with a modulation coding scheme (MCS).
The goal is to make sure that you have acceptable MCS rates everywhere throughout your building. But you need to couple that with installing the fewest number of APs necessary to achieve those MCS rates. It doesn’t matter what your connection rate is if you have too much co-channel interference.
There are several charts freely available on the internet that show expected connection speeds based on channel width, spatial streams, and what MCS rate is negotiated. Here is one example, though you can find others by searching online for “MCS rate chart.”
Reason 4: High airtime utilization is constraining your flow
Airtime utilization can be a revealing measure of how well your Wi-Fi is working. The goal is to limit overhead as much as possible so that most of the airtime is available to service clients. Here is a list of some things that can cause more overhead:
- Too many Service Set IDentifiers (SSIDs): With proper design, networks can be set up with three SSIDs. The first that does 802.1X and uses dynamic VLANs to put client devices in the proper VLAN. The second SSID uses WPA2/3 pre-shared key for any headless devices that cannot connect with 802.1x (typically things like game consoles, streaming sticks, or home automation devices). If you need to put these devices on different VLANs you can use dynamic pre-shared keys (DPSK) to use one SSID but put the devices in different VLANs based on what pre-shared key, they use. The third SSID is an open network for guest traffic.
- Co-channel interference: You want to ensure that two nearby APs are not using the same channel. Make sure you have the proper channel widths set. Check your AP power levels and use dynamic frequency selection (DFS) channels if they are available.
- Slow broadcast traffic: Wi-Fi is a shared medium. Broadcast traffic forces client devices to wait for it to be finished before talking again. Even worse, broadcast traffic is sent at the lowest possible data rate. If you allow a device to connect at 1 Mbps then all broadcast traffic is sent at 1 Mbps because the APs must send it at a rate that it knows every client can hear. That is why it is a good idea to not allow 802.11b clients on your network. You may also consider raising your BSS min rate. That BSS min rate is the slowest connection speed that the APs will allow a client to connect. If your BSS min rate is 12 Mbps and you have a client so far away that it can only connect at 6 Mbps, the AP won’t let it join the network. So, change the BSS min rate carefully.
There are some useful overhead calculators available online to help visualize this. Here is one popular option; you can find other by searching online for “Wi-Fi SSID Overhead Calculator.”
The goal is to get the airtime utilization below 10% when no one is using your network. With regular use, the airtime utilization fluctuates. Because that’s showing you all traffic on your wireless network. That’s why we want to look at that airtime utilization with as little traffic as possible. That way we can get a good sense of how much of that traffic is overhead.
So there you have it. Design-induced Wi-Fi frustrations are real, but they don’t have to be permanent. Remember that your Ruckus SEs are here to help. They have access to planning tools and can design AP placement as well as help you design VLANs and subnets. CommScope RUCKUS can help show you the way forward.