Start-up Divitas Networks is expected to debut this week with technology for tying together corporate wireless LANs, cellular networks and Wi-Fi hot spots as one mobile voice and data network.

The company, founded by technologists formerly with Cisco, Nokia, Sycamore and Verizon, makes an appliance that does many things: VoIP call control; WLAN roaming, handoff management and security; VPN termination; and XML data delivery. The product is intended to let enterprise users with dual-mode voice-over-WLAN(VoWi-Fi) and cellular handsets, or handheld devices access a corporate VoIP and data network from anywhere.

Divitas is to announce itself as a company Monday. Its product is expected to be launched in July.

"So far, the industry has not done a good job with VoIP and mobility," says Vivek Khuller, Divitas CEO. Two issues are the lack of fast roaming and QoS on internal VoIP-enabled WLANs, he says. Another is the complicated technology behind handing off live calls between an internal VoWi-Fi and external cellular network. While dual-mode Wi-Fi/cellular handsets are emerging from Motorola and Nokia, most handsets offer an either-or technology - VoWi-Fi or cell phone calls must start and end on each respective technology and network.

Divitas' Mobility Communications Platform is a Linux-based appliance with customized ASCI software technology. It sits outside a corporate firewall and works with a similar unit running inside the security perimeter. The device inside the firewall ties into a corporate IP PBX via a Session Initiation Protocol trunk, allowing internal IP desk phones and dual-mode sets to be on the same dial plan. An Asterisk IP PBX component on the appliance handles all call control for wireless clients, and also acts as a proxy for external public switch telephone network and cellular network access.

The appliance also acts as a WLAN controller for handset clients attached to 802.11a/b/g networks. It tracks the connectivity status of all Divitas-enabled devices, and manages Layer 2 and Layer 3 WLAN roaming, address translation and QoS settings as users move among WLAN access points.

The Mobility Communications Platform appliance sitting outside the firewall links in dual-mode handsets connecting via a Wi-Fi hot spot. VPN software creates a secure tunnel between the phone client software and the appliance, allowing access to a corporate VoWi-Fi network. The hardware appliances and handset software also run the Divitas Description Protocol (DDP), which communicates the WLAN signal strength and connection quality of the external WLAN. When users move out of signal range of a Wi-Fi hot spot, DDP alerts the appliance, which places a cellular network call to the handset; this cellular call is patched into the live VoWi-Fi call, and the conversation shifts to the cellular network without being dropped, Khuller says.