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
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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