Vendors drive voice over WLAN standard

Deploying voice over WLANs may soon become more commonplace, as leading WLAN equipment vendors are rallying support for a fast roaming standard.

Earlier this month, companies involved in an IEEE study group exploring the need for a fast roaming standard proposed that the IEEE create a formal task group to create a specification. Airespace, Cisco, SpectraLink, and Symbol are in support of the move.

When users of a voice application move from the range of one AP (access point) to the next, the connection must be handed off in approximately 50 milliseconds, otherwise the call may be dropped or the user will hear jitter.

Voice over WLAN vendors use proprietary methods to improve the speed of the handoff because the mechanism in current-generation 802.11 networks is not fast enough.

“The issue is authentication time,” said Bindu Gill, director of technical marketing at Symbol. To maintain a secure connection when a user is moving, the user must be reauthenticated when entering the range of a new AP. “The security implication is that you want to roam fast so you can have good voice quality but you don’t want to compromise security,” Gill added.

The AP must communicate with a database to reauthenticate the user. “Traditionally, that goes all the way back to a server, which may be in another location,” said Chris Bollinger, manager of product marketing at Cisco’s wireless networking unit. That process, however, takes too much time to support a voice call.

Cisco handles fast roaming by designating one local AP as a Wireless Domain Services master. That AP stores a cache of master keys so, as users roam, all APs can communicate with the master AP to reauthenticate.

If the final standard is wildly different than Cisco’s current method, the company will likely support its own technology in addition to the standard.

SpectraLink has a proprietary system that employs a server, which also enforces QoS. The company also supports Cisco’s mechanism.

“We would like everyone to get around one implementation so there’s not a bunch of proprietary methods,” said Ben Guderian, director of marketing at SpectraLink. Furthermore, enterprise customers prefer standards-based approaches, he added.

Details of how the final specification will work are not known yet, but it will involve some sort of local key storage to support faster reauthentication. Although Cisco may implement the standard by storing keys on an AP, others may opt to store such information on a wireless switch.

The IEEE will consider the request for a new task group at a meeting in March. Proponents do not expect to be turned down.

“There’s not a lot of controversy on whether this is a worthwhile thing to pursue,” Guderian said.