When roaming on a wireless network, in very basic terms, here are some things you should look for. You can roam using what I call a tear down and rebuild, i.e. you’re on a wireless network – you then move out of range of an Access Point and your connection is then destroyed and rebuilt on the next Access Point you join. That’s nice, however, if you’re on a FaceTime call or using a VoIP application you’d like this to be as fast as possible. So here are some things to look for and maybe enable on your wireless network. I’m going to explain some Amendments to 802.11 that you should enable and test on your network.
The first is 802.11r, in very basic terms this allows your client to move quickly, your wireless infrastructure needs to support this along with the client having support. Now this comes with some interesting side effects. One, being that not everything supports it. Yes, this has been an option for 10 years, however not all client devices know about it and once again, support it. For example, iPhone 4 and above support it, but macOS does not. However, macOS does support caching of keys to smooth that transition when moving between BSS units in the same ESSID.
Woah? Wait a second, what is BSS and ESSID? OK, let’s step back a little and explain. You’ve heard the term SSID, Service Set ID, this is what you have called your Wireless LAN, i.e. TacoMonkey or FBI Van. Then you have your BSSID, which is Basic Service Set ID. Think of this as multiple Access Points in the same Wireless LAN(technically it’s BSS) using the same name, i.e. SSID. Now an ESSID is the grouping of all those BSS, Basic Service Sets, under the SSID. Lots of times BSSID and ESSID are used interchangeably.
So you have three Access Points, those access points have a BSS and those units all live under an ESSID. Now to route network traffic, each BSS has a MAC address and that MAC address talks to your Client MAC Address. This is how the wireless network knows what Access Point is close to what client and how to move traffic around, because wireless is still Layer 2.
Second thing to look for, is 802.11k, think of this as moving with some visibility, or where it makes sense, i.e. Assisted Roaming. Instead of the client scanning channels and looking around for the same ESSID, the wireless infrastructure will help and provide that information. Most of the time it will be your connected AP then the next AP that the client will be told about. I’ve heard it’s usually around 10 surrounding APs that a client will get information about. This is different depending on what your infrastructure supports. So take that with a grain of salt.
And lastly look for 802.11v. Two main things come along with 802.11v, one being power setting information and another being topology information, i.e. how is this network designed(in simple terms). Why would I care about power settings?
Let us take this example, you have three Access Points in a triangle configuration. Your client is sitting off to one leg of the triangle. If all Access Points in the ESSID are set for 18 dBm, then your client could connect to the furthest physical AP. In some cases that could be fine, however if I’m going to be next to an AP all the time, why not adjust that power a little higher than the others. This will help in assisting where your client should go. A key factor is also understanding how your client will roam, i.e. does it look for a certain RSSI, channel width or preferred wireless band?
Things to remember, not all devices can work with 802.11r, if you have that enabled on your wireless network and require it, your client device might be unable to connect. In the Cisco world they have an “Adaptive” option instead of “Required” for non-11r supported devices to connect. Now remember with 802.11 devices, the client still chooses where to roam, however with 802.11k/r/v, we influence the client to make better choices.
Now that you have an idea of what to look for on your wireless network, how do you know if these are enabled? On macOS, it’s very easy, a Mac app called WiFi Explorer is available. Just make sure you head to Preferences and enable the Amendments column.
A little disclaimer, make sure you check your client devices for support, especially for 802.11r. And, it is best to set up a new SSID to check these settings, also several vendors have 802.11k enabled by default.