802.11n: Plan Ahead

The real-world throughput of 802.11n will be 100 Mbps to 200 Mbps. This is a massive increase compared to the 25-Mbps effective throughput of 802.11a or 802.11g. While a ratified standard isn't expected until 2008, it's never to early to determine how this change will affect your Wi-Fi infrastructure.

First, any decent 802.11n AP should have a Gigabit Ethernet connection; some early products only support a 100-Mbps connection. Next, if you're using a Wi-Fi controller architecture, can the controller support APs operating at these much higher throughput rates? There may be backplane or processing limitations. Some vendors--Trapeze Networks, for example--are moving some functions such as cryptographic processing back to the edge. This reverses the recent trend to centralize as much functionality as possible.

Then there's the question of frequency planning. 802.11n can operate in both 2.4 GHz and 5 GHz, though vendors will choose which frequencies their products support. If you plan to use the double-wide radio channels of 40 MHz, frequency planning is more complicated--especially at 2.4 GHz, which supports three simultaneous normal width channels but only one 40-MHz channel. And while 40-MHz channels boost an individual AP's throughput rate, overall AP capacity does not increase.

802.11n will eventually become the norm, but upgrading won't be trivial. Start planning now. --Peter Rysavy, rysavy.com