This past April, we featured the first of a 2-part series on the Luxul Epic router, Dual-Band Wireless Access Point and Intelligent Network Power Distribution Unit. We were blown away by the performance. As a follow up, we want to bring you a fantastic article by Luxul’s Lindsay Bull that talks about ‘active roaming’. It’s a little wonkish, but if you want great wireless performance, you gotta’ learn this stuff! – D.
When in Roam
Active vs. Passive Roaming Solutions in Wireless Networks
By Lindsay Bull
One of the greatest challenges in deploying WiFi networks for your customers in large residential or commercial spaces is ensuring uninterrupted coverage to mobile client devices—devices that require roaming. So, what exactly is roaming? In networks with more than one wireless access point (AP), it’s the process of a device migrating from an AP with a weak signal to a closer AP with a stronger signal.
Today, many wireless networking companies are addressing this issue with passive solutions that provide “fast roaming.” These products help client devices move between APs at blazing-fast speeds of ~100 ms, which is so quick that the human brain can’t even perceive it. This speed is possible, because with passive solutions, after the client device connects to the first AP in the network, it doesn’t need to be re-authenticated when it connects to another. Information from the original association is passed to the new AP, so it knows the device has already been approved by the authentication server and doesn’t need to repeat the exchange.
While this arrangement sounds ideal on paper, in practice passive solutions have one glaring, inherent problem: the mobile device decides when to drop one AP and move to another. When it’s experiencing a weaker and weaker signal as it moves further away from an AP, it’s up to the device to seek out a stronger WiFi signal, and it will be inclined to put this off as long as possible — let me explain.
Mobile devices—especially phones—are designed to conserve battery life. Performing a WiFi scan uses battery power. To avoid this usage, mobile devices become “sticky,” clinging to the AP they’re on in an attempt to continue getting service from it until the bitter end, even if there’s an AP within range that has full signal strength of -50 dB. As the signal continues to degrade, the WiFi becomes glitchy, with end users experiencing choppy video streaming, slow-loading web pages, or dropped WiFi calls. The device will maintain the connection until the signal strength is down to -85 dB of -90 dB, which is still strong enough to maintain a connection, but not strong enough to pass data. At that point, it experiences failure, and the device finally has to perform a WiFi scan to see if there’s a stronger AP available.
It’s at this point the “fast” in fast roaming comes into play. When the device finally drops the connection to the original AP, it reconnects to the next very quickly. Basically, the only thing fast roaming actually does is make a device reconnect quickly, after it’s already experienced a weak signal.
So, let’s say your customer is connected to her home WiFi network on her smartphone and opens up the Spotify app to stream music as she walks around the house. Eventually, she gets to the end of the usable range of the initial AP. The connection gets so weak that her music pauses to buffer and is then unable to stream at all. Finally, the device drops the connection and quickly reconnects to the next AP with the stronger signal. The cycle continues as she walks around her home from AP to AP. Not exactly a seamless experience.
A different approach to the roaming issue is to utilize active solutions, which are hardware devices on the network—such as wireless controllers—that actively monitor network activity. Such solutions don’t wait for the client device to decide to switch to another AP. They can tell based on signal strength and other factors where each mobile device is on the network in relation to all the APs. If it sees a device is moving further from the AP it’s connected to and getting closer to another, the current AP will send a command to the device telling it to drop the one and connect to the other.
The goal of the active solution is to have the device transition from one AP to another while there is good signal strength from both APs. The wireless controller does this much sooner than the device would on its own, so the in-between period of signal loss never happens, resulting in a WiFi connection that appears seamless.
There are very few companies that offer active solutions. Luxul is one of them with its XWC-1000 and upcoming XWC-2000 wireless controllers as well as the controllers built in to its wireless Epic 3 and XWR-1200 routers. The controllers feature Luxul’s Roam Assist™ technology, which uses signal strength and a proprietary algorithm to determine the optimal time for a device to jump to another AP. While there are certainly other wireless controllers on the market, they are typically only used to manage APs and facilitate their set-up on the network. Luxul controllers are rare in their ability to do both: active roaming and network management. The result is a quick installation for you and a seamless roaming experience for your client.
Lindsay Bull is Luxul’s technical writer and she can be reached at firstname.lastname@example.org.