Ensuring resiliency in wireless LANs

12.10.2012

Traditionally, as the number of mobile devices on a wireless network increases, total available bandwidth per AP tends to decline. Again, this is not a concern in wired access networking; we hardly ever worry about total performance of an access switch decreasing as we connect more PCs to it. Given Wi-Fi is fast becoming the primary network access method, it makes sense to expect a similar level of consistency in performance from WLANs.

If a WLAN is not designed for high-density, the end user can experience what's usually referred to as a "Wi-Fi meltdown," an unexplained halt in network connectivity. Choice of antenna and AP types, proper placement of the APs and appropriate channel planning for increased capacity are all important design criteria, but proper RF design is not always enough to ensure predictable and acceptable performance for mobile devices.

In high-density environments, techniques implemented within the WLAN infrastructure also play a big role. First, the APs need to ensure proper "airtime" allocation, ensuring bandwidth availability for all. For instance, an MacBook Pro installed with a 3x3:3 MIMO Wi-Fi chipset (450Mbps max Wi-Fi link speed) should achieve higher performance compared to the newest Apple  installed with a 1x1:1 MIMO Wi-Fi chipset (65Mbps max Wi-Fi link speed) when both are associated to the same AP. In other words, faster clients should get their job done faster so that there is more airtime available for everyone else. No single group of mobile devices should be able to monopolize network resources.

Wireless engineers can learn a lot about the behavior and expected performance of mobile devices within their infrastructure after simple throughput measurements. Testing the upload and download performance simultaneously is highly recommended since most mobile devices are now powered by which upload data to the network as much as they download.

Secondly, APs should take into account the mobile device behavior in high-density environments. End users, and hence mobile devices, hardly move in locations such as auditoriums, classrooms, company events and meetings. Ideally, their Wi-Fi link speeds should stay consistent when communicating with the APs.