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Robert Liu[May 13, 2005]

Is Dual-Mode WiFi/Cellular Just a Dream?


Imagine the day when you’re talking on your cell phone and, upon entering your office, you’re automatically switched onto your company’s Voice-over-WiFi service. Then at the end of the day, you roam back onto cellular without missing a beat. Well, if you’re waiting for this day, don’t hold your breath!

The expectations for dual-mode handsets have reached a fever pitch with a constant drone from the likes of Bill Gates to the study after study that puts hybrid phones as the next big thing. But technophiles might be disappointed to know that two different technologies addressing the handoff of voice and data packets are being developed independently by separate standards organizations with very different visions of interoperability. And while the two technologies aren’t necessarily mutually exclusive, the underlying business forces are, at times, still diametrically opposed.

"As a security vendor for telecom equipment companies, it's always easier if there were one technical specification to go on. It makes market acceptance faster if there is no uncertainty,” said Bill Anderson, director of product management and marketing for the embedded security division at SafeNet.

Next week, the IEEE (the trade group responsible for shepherding in the WiFi era) will meet in Cairns, Australia, to outline a draft proposal to roam seamlessly between wireless local area networks (WLAN) and other heterogeneous networks. But this time around, IEEE faces a bigger hurdle if it wants to repeat its WiFi success with a new standard called 802.21. Most notably, this is due to the leverage that mobile operators wield over their own cellular network.

Don’t worry. To understand the issues, you won’t need an electrical engineering degree – just a little background. A few years ago, IEEE began studying the coexistence of wireless Ethernet and cellular networks. The 802.21 Working Group came into existence in March 2004.

Around the same time, a tiny cellular services company in the Silicon Valley called Kineto Wireless was conducting field trials with one of its largest customers, AT&T Wireless, using a novel proprietary approach to roam seamlessly between mobile networks and WLANs. But as innovative as Kineto was, executives at the tiny company quickly realized they had little chance of getting their solution into cellular handsets on their own.

“What became clear was that Kineto was a small company and the only way to get handset adoption is if you make this a standard,” explained Steve Shaw, Kineto’s director of marketing.

So to get the ball rolling, Kineto worked on a proposal with handset makers like Ericsson and Nokia. More importantly, operators like Cingular, British Telecom, Rogers Wireless and T-Mobile joined the organic movement. The result is a technology referred to as Unlicensed Mobile Access, or UMA. By September 2004 when UMA was submitted to 3GPP (which governs all cellular standards around the globe) for consideration, it already had unquestionable support from many leading member companies. UMA’s participating companies reads like a “Who’s Who” of the cellular industry.

“With any of these kinds of specification, what really matters is who’s really driving it,” said Cam Cullen, director of product management for Quarry Technologies.

After 3GPP assigned its GSM Edge Radio Access Network (GERAN) body to study the feasibility of UMA, members in January 2005 hammered out a technical specification addressing networking capabilities and service requirements, according to Paul Reid of the European Telecommunications Standards Institute (ETSI). Last month in Dublin, Ireland, members approved the spec to be part of 3GPP Release 6.0.* It is currently in the midst of conformance testing, which is expected to be completed by June, according to Paolo Usai at ETSI.

* While the spec is part of the upcoming Release 6.0, it doesn’t refer to UMA by name. Instead, the specification refers to Generic Access to A/Gb Interface (GAAI), also sometimes referred to as Generic Access Network (GAN). Anyone interested in the spec can find it by searching “TS 44.318 Version 2.0.0.” Don’t you just love engineers?!? I sure do seeing my brother is one.

Meanwhile, on the WiFi side, IEEE was making strides with 802.21. As many as 14 proposals that were once on the table were boiled down to two plans to address what IEEE refers to as Media Independent Handovers. After Cairns, they are expected to emerge with a single unified draft proposal.

“Given we have broad consensus, we should have a letter ballot in another meeting or two,” said Vivek Gupta of Intel, who is author of one of the two proposals currently under consideration. A formal specification then could be ratified by the year’s end or the first quarter of next year, he said.

“The value of dot-21 is hopefully we'll end up with a consistent set of drivers and other middleware entities that provide link layer intelligence and information about the networks in an appropriate way,” Gupta told TMCnet.

But while 802.21 enables data to be freely exchanged (from Layer 2 to Layer 3) no matter what media, UMA sits on top of it at the transport layer (Layer 4) and has its own set of control protocols. How does this hamper interoperability?

“The only thing that UMA does that doesn’t follow what the rest of the industry does is it doesn’t fully [support] SIP for voice signaling. It still uses the 802.11 spec. The voice piece of this is the only thing that doesn’t follow. It doesn’t use SIP for its control protocol. It uses UMA protocols,” Quarry Tech’s Cullen explained.

While SIP is an application layer (Layer 7) protocol that isn’t dependent on any single rule to transport data (i.e. TCP, UDP, etc.), UMA still controls the passing of those packets and that would limit the ability for a device to use IP all the time. What’s worse, there’s even talk that UMA could restrict certain voice traffic that’s so dependent on the transport mechanism. In that scenario, cell operators could for example block calls from Vonage customers, Cullen and others explained.

“Mobile operators want to take advantage of WiFi. They want the cost and performance for the services they have. But if you think about it, mobile operators want a walled garden. They want to control who accesses their network and how they use it,” Kineto’s Shaw said.

“They provide a managed service for us as a consumer. Without a specification for how they can delivery those services over WiFi, WiFi is kind of a threat,” Shaw added. “UMA is the only 3GPP standard that lets mobile operators deliver WiFi over their networks.”

802.21 Working Group Chairman Ajay Rajkumar of Lucent Technologies said IEEE has already opened lines of communications with 3GPP to get UMA to be more 802.21-compliant. But his first order of business is to come up with one “harmonized” proposal. “After a single proposal comes up, there is some draft text available,” Rajkumar told TMCnet.

Even other committee members though don’t believe it will be an easy road. “We're going to try to do that work in stages. All of the things won't happen immediately,” Intel’s Gupta said.

“It's going to be a slightly longer process. We will identify the enhancements that 3GPP should make. It could go on after the dot-21 spec is closed,” he continued.

When asked about the receptiveness of 3GPP to IEEE’s discussions, Rajkumar remarked: “It’s not at that stage yet.”

Robert Liu is executive editor at TMCnet.  Previously, he was executive editor at Jupitermedia and has also written for CNN, A&E, Dow Jones and Bloomberg.  He can be reached at [email protected].


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