Seamless WLAN/Cellular Convergence on the Far Horizon

By James Alan Miller

September 21, 2004

One of the most highly anticipated features promised by dual mode smartphonesthe seamless convergence of cellular and Wi-Fi networksis still a ways off. Motorola and a consortium of vendors have unveiled specifications to bring this to the general public.

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Seamless communications is the holy grail of dual-mode telephone technology. Walk out of your office and out of range of its WLAN during a Voice over IP (VoIP) phone call and you're switched to your mobile handset's GSM or CDMA radio without a hiccup.

Convergence also promises to deliver voice or data over the type of network that is cheaper, more optimal and, of course, available at a particular moment. For instance, say you're talking to a friend on your smartphone while walking down the street. Enter a cafi with a Wi-Fi network, mid-call, and your mobile handset automatically switches to a VoWLAN connection, saving precious minutes and money in the process.

Although one smartphone, Hewlett-Packard's iPAQ 6315, is already shipping with both cellular and Wi-Fi radios and several more are coming—from Nokia (9500 and 9300 Communicators), Motorola (MPx), and T-Mobile (MDA III), among others—none promise to deliver seamless convergence, at least any time real soon.

One mobile handset that will deliver on the promise of convergence when it ships is Motorola's upcoming CN620 Dual-Network Mobile Office Device. Announced back in July, the CN620 is the result of a year-and-a-half collaboration between Motorola, Avaya and Proxim.

Avaya and Proxim provide the WLAN infrastructure equipment to support Motorola's mobile handset in a platform called the Converged Mobility Solution. Because the CN620 is part of this larger platform, you won't be able buy the mobile handset and have it seamlessly switch between a Wi-Fi and cellular network if the WLAN is not part of the enterprise with which the Converged Mobility Solution is deployed.

During a conference call for the launch of the Converged Mobility Solution, Chris White, Director of Business Development at Motorola, illustrated the system by example of a fictional scenerio where an employee using the new CN620 on a train to make a virtual private network connection to the office to get a number, making the call, and then walking into work while still on the phone and having the call switch from GSM to the WLAN while still talking.

More on CN620

The CN620 Dual-Network Mobile Office Device (MOD) has the size and shape of a cellular phone but Motorola has installed a user interface including 9-way navigation disc controller and other buttons for easy access to enterprise phone functions such as hold, mute, and speakerphone.

The screen on the CN620 will use color coding to indicate when it is connected to a metered GSM connection (forest green) or the unlimited WLAN (plum). There's full WAP and HTML-based access for Web browsing, and the phone can synchronize with data stored on PCs.

The phone runs on the Windows CE 4.2 operating system with tweaks made by BSQUARE, which provided platform software and application engineering services for Motorola. BSQUARE engineers wrote components for the Windows CE low-level systems integration with the platform.

What about Everyone Else?

Earlier this month, 14 companies announced the publication of the Unlicensed Mobile Access (UMA) specifications for extending mobile voice and data services over fixed wireless LANs.

The goal of UMA is to let consumers roam seamlessly between their cellular networks and the wireless LANs in their homes and offices with dual mode mobile handsets, such as those mentioned above.

For end-users, the experience should be seamless because it leverages the same mechanisms used in today's cellular networks. But instead of calls be handed from base station to base station, as when you are driving on a highway, they are handed off between an outdoor network and a wireless LAN.

Carriers benefit from this system by being able to deliver their same services—voice, data, SMS, downloads, etc.—over another type of network, Wi-Fi, in parallel to their traditional cellular networks. To compete with VoIP services, operators might offer limited or unlimited WLAN access for a fixed rate of anywhere from $5 to $20 a month on top of their usual mobile access fees.

Commercial deployments of solutions based on the UMA specifications are not expected to deploy until the first half of next year.

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