Lately, I've been focusing on a few of the primary hurdles in running voice over wireless LANs. So far, we've touched on latency, security and location tracking for E911 calls. This time, let's look at how to keep handset batteries from draining too quickly.

Because VoIP packets can arrive at any time over a WLAN, handsets normally operate at full power. This causes a significant drain on a handset's battery life. But some vendors are taking matters into their own hands to alleviate this problem.

Early this month, Aruba Wireless announced a power management scheme unique to voice devices that conserves battery life by maximizing opportunities to turn off the handset radio. An Aruba access point can be partitioned into eight "virtual" APs, each with its own MAC address and service set identifier (SSID). Using the handset maker's configuration utility, network administrators set up VoIP phones to associate to the virtual AP with the SSID and MAC address that use this special power management scheme, Aruba explains.

In addition, last month, VoIP-focused WLAN start-up Meru Networks said it is working with leading 802.11-based phone manufacturers and chip vendors to increase handset battery performance. Meru is providing manufacturers with sleep-mode drivers for handsets that increase talk time battery life by more than 200% when operating over a Meru WLAN, says Kamal Anand, Meru's vice president of marketing and sales. He says Meru's system allows unused functions on the handset's chips to be shut down between transmissions during talk time.
 
For its part, Trapeze Networks says its Mobility Point APs use power-save features that allow phones to implement sleep-mode. The APs will buffer traffic for those sleeping phones, the company says.

Note: This newsletter series intends to give you a flavor for several technical challenges with VoWLANs and recent progress toward solving them. The articles will hopefully provide a starting point for dialog with vendors. But for fully comprehensive information, you should be sure to talk to the various vendors or find a buyer's guide.

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