The last newsletter discussed the high-availability challenge of wireless LANs and the latest move from Meru Networks to manage the RF environment to improve availability. Other vendors are on top of the issue in similar ways.

For its part, startup Extricom, which has an architecture similar to Meru’s single-channel setup, associates client devices to its WLAN controller, rather than to any single AP. APs play the role of simple communications conduit, according to David Confalonieri, VP of marketing. Clients, then, don’t associate with APs and never make handoff or roaming decisions that cause delays or disruptions.

As the client moves in an Extricom network, its uplink transmission can be received by multiple APs at the same time, and, on the downlink, the switch routes each packet to whichever AP transmitter is best positioned at that moment to serve the client, he says.

Note that Ruckus Wireless also uses the many-to-one principle to aid availability by radiating multiple antenna patterns into the environment, then sending an 802.11 acknowledgement (ACK) back to the client across a fast, dedicated timeslot.

Last month, Aruba moved its RF decision-making from clients into the network infrastructure with the release of its Adaptive Radio Management 2.0 software. Among other things, the latest version of the company’s controller software steers clients to the best available channel, choosing the less-cluttered 5GHz frequency, if supported. Trapeze Networks supports a similar band-steering feature.

Here are some other ways vendors differentiate themselves in terms of HA in the client-to-AP WLAN segment:

* Aerohive
Uses a distributed, mesh approach with its APs to automatically route around failures. Doesn’t use a controller, so eliminates a single point of failure.

* Cisco
Has integrated the Cisco Spectrum Expert analyzer, acquired with Cisco’s purchase of Cognio, into its Wireless Control System (WCS), which collectively manages Cisco WLAN controllers. The analyzer finds and identifies any sources of interference, and Cisco Radio Resource Management software recommends what actions to take. Cisco’s Dynamic Power Control also increases or decreases signal power of neighboring APs to ensure coverage, says Sumit Vakil, a Cisco product manager.

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