There has been much talk about the promise of forthcoming 802.11n networks, which will offer at least twice the theoretical wireless bandwidth of today’s 54Mbps 802.11g and 11a networks. In fact, depending on final standards and vendor implementation, most 11n networks might offer 10 times today’s wireless LAN capacity.

Faster is always better, right? Maybe, but one thing to consider is 11n’s potential impact on your existing network infrastructure. In a centralized WLAN architecture, all traffic forwarding and cryptography processing currently take place in a centralized controller. Imagine the load on the WLAN controller suddenly rising by an order of magnitude with the arrival of 802.11n access points (AP). The backplane of your WLAN controller could quickly max out, unless you decrease the number of APs it supports accordingly (compromising your coverage in the process, however). Theoretically, a WLAN controller that supports, say, 120 APs running at 54Mbps today might only be able to support 12 11n APs, for example.

WLAN makers are said to be prepping gigabit uplinks for their 11n APs to accommodate the aggregate traffic of faster 11n clients - about twice the size of today’s AP uplinks. Today’s fastest WLAN controller backplanes run at 8Gbps. That leaves you with a maximum of just eight APs, if they are all transmitting simultaneously, on that controller.

And what if the Ethernet segment to which the APs connect is today a 10/100Mbps architecture? Will you have to upgrade your Ethernet infrastructure between the WLAN controller and AP to gigabit speeds, too?

WLAN systems maker Trapeze Networks is attempting to ready the industry for 11n (and other centralized performance bottleneck issues) with a new overlay architecture it calls Smart Mobile. The setup distributes the forwarding, cryptography, and QoS functions out of the WLAN controller and back into the APs. The controller is left to perform simply management and control-plane functions, such as end-user authentication, mobility/re-association, and rogue-device detection.

Sound familiar? Older, distributed AP architectures performed all WLAN-related functions within the AP, which was beneficial from a performance standpoint. What Trapeze proposes with Smart Mobile is kind of a hybrid between yesterday’s distributed architectures and more modern centralized architectures that aims for the performance of a distributed architecture but the management and control benefits of a centralized one. It also extends the WLAN out of doors under a common management umbrella.

Joanie Wexler is an independent networking technology writer/editor in Silicon Valley.