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Easing The Complexity Of VoWLAN

Setting up a system for voice over wireless LANs (VoWLAN) is complex. Two groups are working toward simplification.

Talking on a mobile handset. For a concept that seems so familiar and commonplace, the underlying infrastructure--and associated complexity-- required to support VoWLANs (voice over wireless LANs) has been somewhat intimidating. Helping to tackle all the related issues and bring some clarity to the marketplace are standards bodies such as the Wi-Fi Alliance and the IEEE (Institute of Electrical and Electronics Engineers). This week, we'll look at what the Wi-Fi Alliance is doing.

Formerly WECA, the Wi-Fi Alliance was formed in 1999 to provide a basic interoperability testing ground for the new IEEE 802.11 equipment flooding the market. Initial standards focused on 802.11b, then on 802.11g and 802.11a, with testing along the way for WEP (wired equivalent privacy) support. In 2002, the alliance developed WPA (Wi-Fi protected access) as an interim but compatible solution for the still developing IEEE 802.11i security standard. Since that time, the Wi-Fi Alliance has become more expansive in its scope.

Early in 2004, the alliance formed the Voice over Wi-Fi task group. Made up of wireless infrastructure, handset and test equipment vendors and headed up by Meru Networks' Chief Software Architect Joe Epstein, this group has focused on two cases: home and enterprise. Similar to the division between WPA pre- shared keys (home) and WPA with 802.1X support (enterprise), the home case is simpler because only one AP (access point) is required, so little emphasis is placed on roaming capabilities. It will include some level of QoS (quality of service), likely in the form of WMM (Wi-Fi multimedia) and perhaps WMM-SA (Wi- Fi multimedia scheduled access). The average number of traditional handsets in the home case ranges from two to four, so security provided via manually entered WPA pre-shared keys should be enough. The MRD (marketing requirements document) for the home case has been completed, and the Voice over Wi-Fi technical task group is now generating the methodology and producing test cases.

With some of the groundwork laid, the home case has been expanded and extended into the enterprise case, where issues such as roaming and battery life become more significant. Because pre-shared keys have limited scalability in the enterprise, network-based authentication schemes will have to be constructed to accommodate the cramped or reduced keypads found on VoWLAN devices. The Wi-Fi Alliance is concurrently working on the "Simple Configuration Security" concept, which ideally will draw on the features found in Broadcom's SecureEasySetup and Buffalo Technology's AOSS. This push-button security mechanism allows even headless devices to create secure connections without a keyboard and monitor. The Voice over Wi-Fi technical task group hopes to complete the enterprise case in the first half of 2006.

Similar to how WPA was an initial subset of IEEE 802.11i, WMM is a subset of the almost completed IEEE 802.11e. WMM is a QoS standard that specifies four levels of priority for traffic, of which voice is the highest. Certification began last September, but the uptake by VoWLAN handset manufacturers has been disappointing. Cisco, which just released new firmware for its enterprise 7920 VoWLAN handset in June, did not include WMM support. SpectraLink included WMM support in its latest release, but the company will continue to pitch its own proprietary SVP (SpectraLink Voice Protocol) in the interim until enterprises support WMM throughout their infrastructure.

Also available are admission control and unscheduled APSD (automatic power save delivery). The first prevents the number of calls and phones on a single AP from overwhelming its capacity. APSD works by having the device sleep during times of non-communication, waking up only to send or receive traffic on a "scheduled" basis. In an attempt to match the talk and standby times of cellular phones with each generation of WLAN chipsets, wireless chip vendors Atheros and Broadcom have placed a strong emphasis on power usage. Coming up in the first half of 2006, the Wi-Fi Alliance will be certifying WMM-SA with the equivalent APSD. Scheduled access is deterministic; therefore, traffic can be planned rather than contended for, as is the case with current access schemes.

Last fall, the Wi-Fi Alliance created the WCC (Wi-Fi/Cellular Convergence) task group, which has been working on a standard relating to combination Wi-Fi and cellular products. Given the fact that mobile carriers have been testing handset interoperability for years, the group is coordinating with the CTIA (Cellular Telecommunications & Internet Association). Until now, the alliance has tested wireless network cards and access points; the move to converged handsets and non-Wi-Fi wireless service such as HP's iPAQ PocketPC h6315 will prove challenging. Wireless data communication test solutions provider Azimuth Systems, working closely with both the Wi-Fi Alliance and the IEEE, has developed a testing solution that enables testing labs and large organizations alike to verify roaming times not just between access points but also from Wi-Fi to cellular and back. Certification should start early next year with a simple SOHO (small office/home office) case and then proceed to the more complex enterprise case thereafter.

Unlike data over wireless networks, it's clear that voice is much more demanding in its QoS, security needs and battery usage patterns. Home networks, without the roaming and authentication concerns, will likely be able to adopt this kind of voice mobility much sooner than enterprise networks. While enterprises have had to perform network evaluations before embarking on wireline VoIP, wireless network planners should take the time to build an infrastructure that will support voice. Doing so will enhance the reliability and performance of data networks, too. Enterprise wireless networks seeking to provide VoWLAN will have to wait and subscribe to a host of standards, fall back on a single vendor such as Cisco or work with any number of the vendor tested and integrated solutions available today.

Frank Bulk is a contributing writer to Network Computing Magazine covering wireless and mobile technologies and works for a telecommunications company based in the Midwest.

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