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Analysis: Voice Over Wireless LAN


Voice-Over-Wi-Fi, or Vo-Fi, is liberating: Employees break free of binding wires and dodge cellular costs, while IT realizes the ROI promise behind WLAN investments. But our tests show that delays in a fast-secure roaming spec could slow adoption in large enterprises, which will be loath to choose between security and voice quality. Moreover, like star athletes with steroid habits, Vo-Fi vendors must break their addictions--in this case, to proprietary methods of accomplishing everything from call access control to QoS--if they hope to move beyond their conventional vertical markets.

In particular, it's high time vendors stopped using ambiguity in the SIP (Session Initiation Protocol) standard as an excuse to remain entrenched in proprietary signaling protocols ... and to keep customers locked into their product lines. An overall lack of adherence to specs among handset makers is unnecessarily limiting choice and raising the cost of doing Vo-Fi.

Sure, standards groups are moving at their usual snail's pace in some areas, including roaming and load balancing. But the IEEE, IETF and Wi-Fi Alliance have made strides in developing open standards that vendors could tap to improve interoperability among enterprise Vo-Fi handsets, WLAN infrastructure devices and PBXs.

It's not only fear of lock-in that's slowing adoption. Performance is also a limiting factor: Data apps, such as e-mail and Web browsing in fixed locations, rarely taxed the average enterprise WLAN's ability to deliver quality service. Voice is significantly more demanding. Despite their apparent simplicity, single-mode Vo-Fi phones demand attention to signaling, power optimization, fast and secure roaming, call-admission control, and load balancing. Dual-mode phones add a twist: radio interface with cellular networks and the need for coordinated hand-offs to the company PBX. With an upper limit of eight active calls per Cisco AP, densely populated sites may experience saturation. And lack of QoS could hobble your Vo-Fi initiative if you're not careful, especially since the standardized wireless QoS method has been slow to be supported.

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