Wi-Fi networks need an upgrade for Draft N

Draft N Wi-Fi speeds will demand a lot more throughput on the backbone. Vendors may have to rejog their architectures to cope.


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 54 Mbit/s 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 centralised WLAN architecture, all traffic forwarding and cryptography processing currently take place in a centralised 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 54 Mbit/s 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 8 Gbit/s. 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 10/100 Mbit/s 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 centralised 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 centralised architectures that aims for the performance of a distributed architecture but the management and control benefits of a centralised one. It also extends the WLAN out of doors under a common management umbrella.

Best of both worlds? Trapeze wireless LANs are based on a centralized, or “thin-access point (AP)” model, which delivers the centralised management and control capabilities required for scaling large wireless networks. This model is commonly being adopted by many large organisations for new deployments. In addition to Trapeze, centralised WLANs are supplied by Aruba, Bluesocket, Cisco, Meru, Symbol and others.

The Smart Mobile software overlay from Trapeze distributes a so-called station switching record (SSR) of every 802.11 client to each of Trapeze’s Mobility Point APs (while also retaining the information inside the switch). The SSR enables most application traffic to be switched within the APs themselves, alleviating potential data bottlenecks at the central WLAN controller.

However, you may choose to keep other application traffic, such as guest access traffic, centralised, says Dan Simone, Trapeze VP and CTO, to ensure that it doesn’t traverse internal switches.

Smart Mobile also extends the edge of Trapeze WLANs to the out of doors. A hardened, Smart Mobile-enabled Mobility Point can be configured to run in mesh mode, says Simone, enabling the system to be used for backhaul and campus-area coverage. A common management system, the company’s Ringmaster tool suite, will control both indoor and outdoor WLAN segments, Simone says.

The “meshedness” of Smart Mobile is its most appealing characteristic to Frank Basso, assistant director of communications at Mazda Raceway Laguna Seca, in Monterey, Calif. The outdoor raceway currently uses Trapeze gear for 802.11 client access in concert with WiMax backhaul equipment from Motorola and Trango Broadband Wireless to support public access, corporate, concession, point-of-sale, ticketing, hospitality and other applications. Basso indicated that he prefers to run one “big” Trapeze network that spans the 500-acre track.

The move means that Ringmaster site survey tools should also work out of doors, says Basso. Previously, Ringmaster wasn’t able to account for elevation deviations, metal tractor-trailers and other outdoor variables in helping build a network configuration, he says, for which “I gave [Trapeze] a lot of grief.”

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