Have you ever noticed how while standing in one place the Wi-Fi network works great, but while walking around the building you get disconnected or the performance drops drastically? Well, the reason for these issues you have encountered is problems with Wi-Fi roaming, which regretfully is one of the most common reasons for Wi-Fi connection and performance problems. After all, roaming behavior is hard to predict, and it is one of the most difficult parts of supporting a BYOD (bring-your-own-device) environment. Not only do different devices roam differently, but sometimes a single Wi-Fi device will change its roaming behavior if a different application is running, there are too many AP’s nearby causing congestion or the AP’s are misconfigured. The good news is that testing for roaming problems is very similar to testing for probing behavior. Since probing is the first step of roaming (probing is what a client device does when it’s looking a for Wi-Fi network to connect to), thus troubleshooting roaming problems is a lot easier than it may seem.
The most common reasons for Wi-Fi roaming problems are:
Signal Coverage – Bad signal coverage is one of the most common reasons for Wi-Fi roaming problems. If there are areas of your building with no Wi-Fi signal between AP’s (no signal overlap), then client devices will get disconnected from the network while trying to roam from one AP to another.
Unconnected Devices – It seems counter-intuitive that an unconnected Wi-Fi device could affect performance more than a connected device, but that’s how Wi-Fi works. The problem is Airtime, which can be defined as the time a Wi-Fi signal spends on the air. The accumulated Airtime taken up by probe requests (which are transmitted at low data rates) sent by unconnected devices can often be greater than the accumulated Airtime taken up by network data. Because of that, when a client device sends a probe request during the roaming process it must wait a long time for an AP to reply, thus causing the roaming process to be slow or fail
Congested Networks – Adding new APs to help improve coverage or performance on wi-fi networks seems to be the first step for most IT professionals; however, adding new AP’s could mess up the whole RF design, and result in network admins creating more problems than they are solving. As a new AP is added you increase the amount of signal overlap (signal of multiple AP’s covering the same area), so you may end up having areas of your building on which you have a strong Wi-Fi signal coming from multiple AP’s. Client devices that are ready to roam will look for AP’s with a strong signal to roam to, so what happens is that if a client device finds multiple AP’s with a strong signal covering the same area it will have problems trying to decide which AP it should connect to (they all have a good signal). This will delay the roaming process, thus affecting the performance of the applications being used.
AP Misconfiguration – AP controllers are great for configuration and management of many APs in a common network, but they are not perfect, and configuration errors do occur. For example, if all APs on a network are not configured with the same basic settings, roaming will fail. Some of the settings you want to make sure always match are: SSID, Type of Security, Security Credentials, SSID Transmission (hidden or not).