Proxim's Cellular Coupling

The problems of integrating voice services on wireless LAN networks with their cellular cousins has been exercising access point vendor Proxim Corp. (Nasdaq: PROX) and its partners, Avaya Inc. (NYSE: AV) and Motorola Inc. (NYSE: MOT), for over a year now (see Trio Combine For Convergence).

So, on a visit to Unstrung's top-secret underground bunker Thursday, Proxim explained some of the issues involved in enabling people to roam between two very different types of networks and how – at least initially – fixing them won't require the cooperation of the cellular carriers.

It’s okay, it's just sleeping: One of the major problems of enabling voice services on 802.11 networks is that standard wireless LAN client hardware requires a lot of power to do its thing, making it tricky to use with smaller, battery-powered devices such as mobile phones.

Therefore, says Proxim's chief technology advisor Leigh Chinitz, a lot of work has gone into ensuring that dual-mode cellular/WLAN handsets from Motorola will offer the same kind of performance as standard models (see Motorola Plots WLAN VOIP Move).

"People are going to expect hours of talk time and tens of hours of standby time from their phones," says Chinitz.

Currently, wireless LAN networks constantly ping client devices in the neighborhood, so one way to lessen power consumption is to let the client tell the network when its ready to start talking, says Chinitz. "The infrastructure will not send anything to the handset until the handset lets it know it is available," he explains.

Basically, wireless LAN phones will conserve power by "sleeping" – a lot.

PBXstasy: An IP-PBX (private branch exchange) is also an essential part of Proxim's planned WLAN/cellular integration moves. It is the ability of the phone to "talk" to the PBX and vice versa that allows Proxim and friends to bypass the cellular carriers for the time being.

For instance, the phone sets up a call on the wireless LAN network using session initiation protocol (SIP) signaling, but the "intelligent" PBX controls how and when the data it transmits is broadcast on the network. The role of the PBX becomes even more important when a user roams away from the wireless LAN onto a cellular network. As it detects that it is moving out of range of a wireless LAN network, a user's phone will search for a suitable cellular replacement. Once it finds one, the phone calls into the PBX, which then handles the data routing. This is how Proxim et al. plan to move between networks, at least for the time being.

"Right now… it doesn't require the cooperation of the carrier… it's more of a loose coupling," says Chinitz.

Later on, the threesome plan to develop a more "classic cellular handoff model… a tight coupling with the carriers," says Chinitz [ed. note: that's what everyone wants really, isn't it?].

We'll have more on the building blocks Proxim plans to use to build a suitable VOWLAN infrastructure, oh, real soon now.

— Dan Jones, Site Editor, Unstrung