March 23, 2006
 

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Posted: 11.04
Wi-Fi Finds its Voice
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Wi-Fi isn't just for data, but adding voice involves more than simply buying 802.11 phones.  

By Tim Kridel




The Pacific Sunwear clothing and accessory brand projects an image of always being on the go—which is a great way to appeal to teens but the wrong image to project when you’re trying to do business.

“Key management and support personnel were often away from their desks and weren’t reachable via telephone,” says Ron Ehlers, the company’s VP of information services. “Since they were away from their desks, they didn’t receive and couldn’t respond to voicemail messages in a timely manner.”

The solution? Voice over wireless LAN (VoWLAN), which uses 802.11 Wi-Fi networks to support phones alongside the usual assortment of data devices, such as laptops and PDAs. VoWLAN’s business case is a familiar one: Like cellular, the constant link makes employees more productive and easier to reach. “Although not quantified, we have seen productivity gains, time savings, cost savings, improved decision-making and greater sharing of information” since the VoWLAN was deployed, Ehlers says.

There are ways to calculate the ROI for a VoWLAN system, particularly in companies where employees rely more on cellular than desk phones. “Their telecom expenditure has gone through the roof as a result,” says Ken Kolderup, VP of marketing at Kineto Wireless, which makes infrastructure that lets cellular operators support WLANs. “Cellular service is 25 to 30 percent of most companies’ IT spending.”

By tallying the amount spent on cellular service and then breaking out the amount of minutes used in the office, a company can estimate how much it would save by shifting those minutes to its WLAN. The next, more complicated step is to figure out how much of the existing infrastructure—particularly the WLAN and the PBX system—can
do double-duty with voice and data. It’s here where many companies get tripped up.

Coverage and Capacity

For enterprises with an existing WLAN, the most common mistake is assuming that it can handle voice as-is. “They say, ‘We’ve got Wi-Fi coverage because everybody can use their laptops in the conference room,’” says Ben Guderian, director of marketing at SpectraLink. But a seamless VoWLAN system requires coverage in other areas—such as elevators, stairwells and even bathrooms—where employees don’t use laptops but do use cell phones. Adding access points (APs) is the obvious way to achieve seamless coverage, but deploying them willy-nilly can hurt the ROI. A smarter move is to use design tools—such as Connect802’s Suite Spot Predictive Site Survey—to understand how cubicles, walls and other factors affect WLAN coverage.

Just because laptop users can connect in an area doesn’t mean that voice users will be able to make calls there, too. That’s because a data session can tolerate a weaker signal and the latency that occurs when lost packets are resent. Making a voice call in the same location might not work, or it may force users to resort to “Huh?” or “Roger that”—or, worse, to cellular, defeating one of the reasons for deploying VoWLAN in the first place.

Another often overlooked factor is capacity. For example, an AP that does just fine serving laptop users in a conference room might not be able to handle the load when a meeting adjourns and attendees all flip open their VoWLAN handsets to check voicemail. High-traffic areas may need multiple APs, depending on how many calls each one can handle. For example, each AP in Motorola’s 802.11a-based system can handle up to 25 simultaneous calls. “That’s reserving 50 percent of the bandwidth for data, and we’ve also reserved a little bit for 911 calls,” says Chris White, Motorola’s director of business development for seamless mobility.

The entire WLAN also may need to be partitioned so that, for example, someone sending a 20MB PowerPoint file doesn’t suck up all the bandwidth on an AP and knock off its voice calls. Although new and forthcoming Wi-Fi standards such as 802.11e will provide more quality-of-service (QoS) mechanisms, today’s technologies can deliver reliable voice and data service—assuming that the WLAN isn’t overloaded or underbuilt. “What we’ve seen is that without explicit methods of QoS, voice service works very, very well in the vast majority of WLANs,” says Kineto’s Kolderup.

Opinions differ over whether 802.11a is a better choice for voice because it uses a band that’s somewhat less congested and it offers more channels. For example, Motorola recommends leaving the existing 802.11b infrastructure for data and adding an 802.11a overlay for voice and the most demanding data applications. “We use 802.11a because to do proper overlapping channels, ubiquitous coverage and frequency planning, we need more than the three frequencies we get with 802.11b and g,” says Motorola’s White. “The nice thing about 802.11a is that we have at least eight frequencies to use.”

The decision usually rests on factors such as whether the enterprise wants to re-use its existing 802.11b infrastructure or whether it’s already planning to migrate to a or g. In a well-engineered WLAN, 802.11b isn’t necessarily an inherent weakness. Says SpectraLink’s Guderian, “We haven’t run into too many capacity problems running 802.11b.”

Leveraging Legacy

A third factor is compatibility with existing systems. One example
is the PBX, which may have to be upgraded to support voice over IP (VoIP), depending on the VoWLAN solution. “If an enterprise already has a VoIP-wired infrastructure—a card in the PBX or an SIP gateway—it’s very easy to extend that and support voice over wireless,” says Vipin Jain, VP of LAN access at Extreme Networks. “The incremental cost is not significant. If you don’t have VoIP infrastructure, then it becomes a question of ROI.”

Choosing the gateway option now doesn’t necessarily mean buying new VoWLAN devices if the PBX is upgraded to VoIP in the future. “In most cases, a handset that a user would deploy today behind a gateway can download new code in the field to support direct IP connections,” Guderian says. “So when they do migrate their PBX to an IP-based platform, they don’t have to throw out the handsets and start again.”

At Pacific Sunwear, for example, SpectraLink’s VoWLAN system integrated seamlessly with the company’s existing Lucent Definity PBX and Cisco 802.11b WLAN. “The users have access to all features of their desktop phone, including Audix voicemail,” Ehlers says. “Anyone calling their desktop extension rings through to their wireless SpectraLink handset.”

There’s also the human factor: A good VoWLAN system shouldn’t have a steep learning curve. For example, from a provisioning and management perspective, the handset should look and act just like any other 802.11 client, so that adding a VoWLAN phone is no more complex or different than adding a Wi-Fi PC card modem. The only potential hitch is that other departments besides IT may need to become involved, because tasks such as assigning extensions and setting features and restrictions are traditionally handled by the department that’s responsible for the company’s phone system.

What’s Next

Today, data users have numerous hardware and software options for seamlessly switching between cellular networks and WLANs, both public and private. Voice is headed in that direction, too.

Cellular-WLAN interoperability should get a boost from Unlicensed Mobile Access, a new industry group that’s developing open standards to support seamless switching between GSM/GPRS and unlicensed technologies such as Bluetooth and Wi-Fi. Backed by AT&T Wireless, Kineto Wireless, Motorola, Nokia and T-Mobile, the UWA published its first set of standards in late August, and the products based on the specs are slated to hit the market in 2005.

Several options already exist. For example, the Motorola CN620 handset supports 802.11 and GSM/GPRS and allows voice calls and data sessions to hand off automatically as the user moves in and out of coverage. Instead of separate cellular and enterprise phone numbers, users have a single number. The CN620 works with network infrastructure that tracks which networks the user is in range of and then routes incoming calls accordingly.

The CN620 also has relatively impressive battery life, considering that 802.11 is notorious for sapping batteries. “Wi-Fi is a battery hog, end of story,” White says. “But we’ve done some creative things with low-power processors and sleep modes that let us conserve battery life. [In WLAN mode], we’re seeing three hours of talk time and 80 hours of standby time.”

Another trend is toward support for push-to-talk (PTT), which is a good fit for sectors such as manufacturing and healthcare. PTToWLAN solutions are available today from vendors such as TeleSym, whose client software reprograms a Wi-Fi PDA’s record button for use in PTT. In the future, PTT will work across systems. For example, as more GSM operators deploy PTT, Motorola plans to expand its system so that a WLAN user can use PTT to communicate with a colleague on a GSM network.

That flexibility has some vendors convinced that cellular-WLAN handsets will quickly jump from the exception to the rule. “The pure VoWLAN handset will be obsolete in the next year to two years, as multi-mode handsets become prevalent,” says Extreme’s Jain. “VoWLAN handsets are a niche.”•

Tim Kridel is a California-based freelance writer who covers technology.
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