Cellular/Wi-Fi convergence wins over some early users

Early products and services that shift voice calls seamlessly between wireless LAN and cellular networks are proving themselves to enterprise users.

Early adopters, including those still in pilot projects, say the handoff between two, different wireless connections is generally unnoticeable and almost always reliable. These convergence capabilities also give mobile phone users at least some of the features offered by the corporate PBX, such as transferring calls or dialing a four-digit extension.

Nevertheless there are two recurring issues: the need for a pervasive WLAN designed with voice in mind, and the fact that the 802.11 radio on these so-called dual-mode mobile phones depletes batteries far more quickly than cellular radios do.

The users interviewed for this story are using two kinds of solutions for what's often called fixed-mobile convergence (FMC). One is a behind-the-firewall FMC server or appliance from a third-party vendor -- from big companies like Siemens and NEC, as well as newer, smaller companies like DiVitas Networks and Agito Networks. The server typically coordinates with a corporate IP PBX and with a client application loaded onto a mobile phone that has cellular and 802.11 radios.

The other convergence solution is a carrier service, using the Unlicensed Mobile Access (UMA) standard from the Third Generation Partnership Project to shift calls between an unlicensed Wi-Fi WLAN and a GSM carrier's licensed cellular network. In effect, these services shift the FMC server functions to a UMA controller on the carrier's network. In the US, T-Mobile offers a UMA service to residential and business customers.

Wherever it's located, this server works with the client application to detect when a user is moving into and out of range of cellular or Wi-Fi networks. Basically, the server starts a parallel call over the alternate wireless network; when it's secured, the server mixes the audio from the two sessions and drops the first wireless connection.

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The law firm of Orrick, Herrington & Sutcliffe has been trying out Agito's product at its four-building campus for several months with a handful of lawyers and IT staff. The technology could give the firm's 1,000 lawyers a single phone number, on a single phone, with PBX features on their mobile handsets, and better in-building wireless coverage (via a WLAN), says Patrick Tisdale, the firm's CIO.

"We don't see this as a money-saving opportunity," Tisdale says. "We're not sure that actually happens." The value lies in being able to get calls to and from the firm's lawyers wherever they might be in the firm's buildings, all via a single device.

The Agito server coordinates with a Cisco Call Manager, and the client phones (Nokia N95s) are visible to Call Manager via Session Initiation Protocol (SIP). With the Wi-Fi interface, attorneys find they can connect wirelessly to their broadband router at home, and make a four-digit call to any extension in any of the firm's offices nationwide, says Nellis Freeman, information services manager for the Menlo Park campus.

The University of California San Francisco Medical Center is considering a wider deployment of dual-mode handsets with the DiVitas server, but the pace will depend on the gradual upgrade of the Cisco 802.11b WLAN to 802.11a/b/g, says Davd Sproul, manager of emerging technologies and IT capital projects for the center.

"We went with DiVitas to get seamless roaming [from cellular to WLAN] for doctors' voice calls," Sproul says. "They wanted the call to not drop when they walked into or out of the building." The hospital now does expect to save money on cell plans but isn't sure how much, he says. A study of cell phone use found that about 60 per cent of the mobile calls were between medical center staff within the campus. Shifting these to run over the WLAN will save those cellular minutes.

The hospital recently added 25 handsets, in three Nokia models, to the eight previously being used, and users are clamoring for the new phones, Sproul says. The wider deployment will let the IT group get more experience in supporting and running the system, especially on the client side. Sproul says the DeVitas beta server ran for more than 18 months with no problems.

The biggest complaint has been battery life. Initially, the dual-mode phones barely got eight hours, a problem when nursing shifts are 12 hours. Nokia has made some tweaks at the handset level, and the phones now get about 10 hours from the battery.

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Handing it to the carrier

UMA-based services do away with the need for an on-site server. Instead, these functions are shifted to the UMA controller in the carrier network, acting as an interface between the IP world of a WLAN and the mobile carrier's core network. Kineto Wireless is a UMA vendor, and T-Mobile uses the gear for services like Hotspot @Home."

One company testing out T-Mobile's UMA offering is Anthony Marano Company, a family-owned fresh-food distributor. The company since 2004 had been using a jointly developed, dual-mode solution from Motorola, Proxim Wireless and Avaya, with dual-mode handsets, a 75-access-point 802.11a WLAN, and a SIP-based PBX with software to manage the handoff with the cellular network. In general, the systems worked well, says CTO Chris Nowak. But one problem is a wireless "speed limit": Employees zipping around the 460,000-square-foot warehouse on pallet jacks or other vehicles lost the Wi-Fi connection when they drove at more than a few miles per hour.

The company wants to upgrade, and last fall deployed a pilot WLAN from Extricom, with six antennas distributed through the warehouse, and about 50 UMA-enabled BlackBerry 8320 handsets with built-in cameras and Bluetooth, on T-Mobile's cellular network. Extricom uses what it calls a channel-blanket architecture. The 802.11 media-access-control functions run entirely on a central controller, so the "access points" in the warehouse are nothing more than antennas. There is no handoff among them because the entire system in effect works as one access point.

The sleek new BlackBerries "see" the Wi-Fi network via a one-time scan. The user enters a key, and the device registers via IP and the Internet with the T-Mobile UMA controller. The controller "knows" where each handset is, uses the appropriate wireless connection for the voice call and shifts between them seamlessly. "I'm happy not to know how all this works, as I have to know with the Avaya gear," Nowak says. The handover "works most of the time and that's good enough for us," he says.

The Extricom WLAN has been a key element in the quality of the service. "We're not worrying now about co-channel interference," Nowak says. "That was a constant issue [in the past]. We were constantly changing [radio] power levels and channels to make it 'just right.'"

Nowak is evaluating the additional capabilities the carrier can offer, as well as the degree to which T-Mobile will be able to offer PBX-like functions and how important they are to Anthony Morano.