While mobile VoIP technology is finding a home in hospitals and manufacturing plants where workers need to stay connected as they roam, rollouts still require painstaking work, users say.

At San Antonio Community Hospital in Upland, Calif., VoIP is second on the list of applications being implemented over the facility's Wi-Fi network - right after bedside and operating-room computer access to patient records and X-rays, says Irv Hoff, the hospital's manager of converged networks.

True mobility and cost were major concerns Hoff had to overcome about Wi-Fi, but he is now convinced the technology meets his needs. Still to be worked out: details of deploying VoIP to avoid problems such as calls dropping between access points and barriers within buildings blocking calls. "We want the quality of the call to be equal to what you expect from a wired phone, given that we control the environment," Hoff says (read other hospital case studies).

Voice on Wi-Fi combines two sets of trouble
The problems are complex because VoIP over Wi-Fi combines the issues of wireless LANs (WLAN) with those of IP telephony. As WLANs for data become more and more accepted, so will VoIP over Wi-Fi, says Will Stofega, an analyst with IDC, but the potential problems with VoIP must be dealt with first. "If there is packet delay or loss, you hear it with VoIP," Stofega says. And as Wi-Fi VoIP phones proliferate, phone calls will boost the demand on wireless networks. "If you give people mobility on the LAN, you have to increase the number of access points," he says (read our summary of the troubles: Voice on Wi-Fi? Just say No) .

Despite such issues, Wi-Fi networks are growing, with worldwide sales of wireless mobile network infrastructure gear projected to rise from about US$43 billion last year to $49 billion by the end of 2008, according to IDC. As network executives get comfortable running data over these networks, they will increasingly add VoIP, Stofega says. At the moment, VoIP over Wi-Fi use is very limited. As the technology advances to make its use easier and to assure voice quality, that use will increase, he says.

Vendors selling access points and switches capable of supporting VoIP include Airespace (which is being bought by Cisco), Aruba, Cisco, Siemens (which owns Chantry) and Trapeze. According to Siemens, the top users are hospitals, retail stores, manufacturers and warehouses.

Keys to deployment
For Hoff, the first step is making sure access points in the hospital cover every location an end user might go in the building. Then he has to make sure there are enough overlapping access points to support the likely load of simultaneous users without denying service to any of them. He is using Trapeze gear and a tool the company provides called RingMaster (read our Trapeze review) that maps buildings and the effective penetration of Wi-Fi frequencies through walls, floors, doors and windows.

This is a particularly big issue in hospitals, where renovations that change the configuration of walls are common, but also because some of these walls are shielded to block X-rays and are therefore unfriendly to Wi-Fi transmissions, as well. "We do a lot of remodelling - new partitions, new offices," Hoff says. It's an ongoing process, so as the hospital makes changes it records them in RingMaster, which identifies new blind spots. Then access points are reconfigured to get around them.

Load balancing among access points is key to efficient distribution of calls, vendors say. Airespace access points, for one, distribute users evenly in environments where they might be within range of several devices at the same time. Without this feature, user gear would vie for entry to the access point with the strongest signal. Siemens says its next round of Chantry devices will include this feature.

Assuming there are enough access points to guarantee coverage, network executives have to ensure fast handoffs between devices as callers walk in and out of range of different sites. The switchover has to take less than 50 milliseconds or callers can hear it - this means careful network design is essential. For instance, with voice and data running on the same network, the handoffs can take from a half second to 10 seconds, with the presence or absence of data on the network affecting the time unpredictably, according to Network World testing.

Beyond network performance, any use of VoIP over Wi-Fi should include an evaluation of voice quality. "Do you want to be on a call with a client and barely be able to hear?" Stofega says.