Unlike 802.11 Wi-Fi, WiMax incorporates QoS (quality of service) by assigning each device using its service an access slot. Depending on the overall use of the WiMax network and the kind of traffic the device requires, this slot may expand or shrink, but a device is also guaranteed a minimum amount of access to the network. In contrast, it's all too possible for a Wi-Fi AP to be overwhelmed by multiple clients demanding simultaneous access.

It also delivers mobility to its clients by enabling ground stations to switch data transmissions as a mobile client moves between them. For practical purposes, 802.16e uses two different approaches. In the first approach, soft handoffs require a mobile station to make a connection to the next base station before switching off from the old base station. This works well for voice, multimedia, gaming and other latency-sensitive applications. It's inefficient, however, for delivering normal Internet traffic such as Web browsing or e-mail, which tend to come in data bursts.

For this kind of traffic, a hard handoff, or break-before-make, works better. As the name implies, when Internet IP traffic is detected, the mobile WiMax devices first disconnect from one base station, for a delay of up to 50 milliseconds, before connecting to the next base station.

In addition, 802.16e added other features to improve its utility. Like 802.11n, mobile WiMax incorporates multiple input/multiple output (MIMO). MIMO enables networks to work efficiently with multipath distortion, which occurs when broadcast signals not following a line of sight bounce off large objects and end up out of sync, thereby scrambling the received transmission. MIMO turns this commonplace problem into an advantage by descrambling the distorted signals.

Unlike 802.11n, 802.16e is an established standard with broad vendor support. The WiMax Forum has two certification labs: one in Malaga, Spain, and the other, which just opened, at the University of Maryland in College Park, Maryland. For a device to pass certification, it must show that it interoperates with other vendors' 802.16e equipment.

Do keep in mind that mobile WiMax is still in the process of being certified and deployed. That said, all the signs indicate that within the next year, mobile WiMax will become a serious contender for your networking budget dollars. You won't want to deploy mobile WiMax in the next quarter, but you should start considering whether it's a choice for your company in 2009. It really is coming in that fast.