Femtocells or VoWLAN?Femtocells or VoWLAN?

Cellular telephone service remains an anomaly in modern enterprise communications, as it represents a separate, stand-alone communications network that is not integrated with anything else in the network infrastructure. Couple that with the fact that cellular is typically the fastest growing and most poorly managed element in our service mix, and you begin to understand why the topic of fixed-mobile convergence (FMC) or the idea of integrating cellular and wireless LAN technologies is getting so much attention.

Cellular telephone service remains an anomaly in modern enterprise communications, as it represents a separate, stand-alone communications network that is not integrated with anything else in the network infrastructure. Couple that with the fact that cellular is typically the fastest growing and most poorly managed element in our service mix, and you begin to understand why the topic of fixed-mobile convergence (FMC) or the idea of integrating cellular and wireless LAN technologies is getting so much attention.As we move into 2008, we will have to begin choosing among the various ways in which FMC can be implemented. Among the strategies being proposed are:

* Use cellular service as our mobility solution and address the problem of poor indoor coverage with a distributed antenna system (see Joannie Wexler's article in the Dec 2007 BCR and here).

* Use cellular service with femtocells that transfer cellular calls to a small Internet-connected base station when the user comes within range.

* Use cellular service in conjunction with the Simultaneous Ring/Extension-to-Cellular capabilities in the IP PBX. In this scenario, the IP PBX rings calls to both the user's desk phone and their cell number; the user can answer the call on either device, and then manually transfer it from one to the other.

* Employ dual mode WLAN/cellular handsets and let the user manually select which network will handle the call.

* Employ dual-mode WLAN/cellular handsets but have a controller like those from Divitas or Agito Networks that automatically routes calls over the WLAN when the user is within range.

* Use a cellular carrier's FMC with dual mode WLAN/cellular handsets, and have the carrier manage the call handoff, as we see in T-Mobile's [email protected] service.

There are a couple of other options as well, but they're essentially minor variations on one of these basic themes.

The major dividing line among these solutions is how they carry the call once it's handed off from the wide area cellular network. In particular, will that short haul radio link use Wi-Fi or cellular technology? I think the answer will be different for the consumer versus enterprise markets.

Consumers Go Femtocell The two options for consumer FMC are pictured in the Figure below. You will note that in both cases, the alternative to the wide area cellular connection is VoIP over the customer's broadband Internet connection. That short-range wireless connection can use either Wi-Fi or cellular technology.

T-Mobile did make a big splash with the introduction of their UMA-based [email protected] service in 2007, but the solution doesn't have legs. The basic problem is handsets. With any FMC service, whether it's Wi-Fi or femtocell, you can't just use any handset. The handset needs software that recognizes it's within range of a usable local network alternative, and coordinates the handoff with the network. Using Wi-Fi as the local delivery option means the customer needs a dual-mode Wi-Fi/cellular handset. While the Wi-Fi Alliance identifies over 100 dual mode models, only a handful are available in the U.S.; T-Mobile's service currently supports three.

In a femtocell solution, you just need a cell phone with the appropriate software, while the cellular/Wi-Fi approach requires a more expensive dual-mode device as well as the software. Given the additional cost involved in dual mode devices and the cellular carriers' rather dim view of Wi-Fi, you've got to bet on a cellular/femtocell solution.

Enterprise Goes Wi-Fi Wi-Fi should have a much stronger role in enterprise FMC. I reviewed the options for enterprise FMC last May in a BCR column aptly titled "Clearing Up Fixed-Mobile Confusion". In enterprise FMC, the options can be categorized as:

* Non-Integrated Dual-Mode Handsets: User selects network.

* PBX-Controlled (Manual): Simultaneous ring with user-initiated handoff

* PBX-Controlled (Automatic): Calls are automatically routed over the WLAN when the user is within range (e.g. Divitas, Agito Networks)

* Carrier-Controlled (Manual): Transferring calls from the carrier's network to the private network requires the user to input a code (e.g. Sprint's Wireless Integration).

* Carrier-Controlled (Automatic): An enterprise version of T-Mobile's consumer-oriented [email protected] service.

Right from the start, it should be obvious that any solution that depends on users doing the right thing (i.e. using the WLAN alternative when it's available) is not going to save money. Give the user a dual mode handset and a choice, and they'll just use it as a cell phone. That should put a damper on the dual-mode handset and PBX-Controlled (Manual) options. The same can be said for solutions that require the user to manually transfer the call between networks; they'll just use the cellular network.

A Carrier-Controlled (Automatic) solution where the cellular network transfers calls to a customer's private network just like a cell-to-cell handoff would be ideal, but the carriers have been reluctant to offer that. At their Focus conference last year, AT&T was promising that type of service for 2008, but we'll have to see if they actually deliver. For their part, Verizon is still committed to being fully committed to the idea of FMC.

The carriers' reluctance to offer that type of service has opened the door to solutions like Divitas and Agito Networks that use a special controller on the IP PBX and special software in the handset to automatically route calls over the WLAN when the user is within range. However, those solutions require all calls to be routed through the IP PBX so calls to the user's cellular number are "hairpinned" through the IP PBX, tying up two trunks, and you're still paying for an inbound cellular call.

The carriers like the idea of the customer simply using cellular as their mobility option, but that's because they have never understood enterprise communications. Even if the cellular signal is "5-bars" inside the facility, cellular service does not provide the features we need for an enterprise--not to mention all of the new tricks we're trying to mobilize with unified communications solutions. They've also discussed the idea of using a cellular-only solution for highly-mobile users while maintaining a separate wired telephone system for people whose jobs do not require mobility. Great, we can operate two separate, non-integrated voice networks.

Conclusion FMC is one of the most challenging opportunities we will be facing in the coming year, but it is important that we don't confuse consumer and enterprise requirements. For a consumer who has chosen to do without wired telephone service, FMC is a great way to save their cellular minutes when they're at home. Femtocell technology is the simplest way to get that done.

The functional requirements for enterprise customers are far more challenging however, and that puts WLANs back in the picture. The cellular carriers will have to start offering services that really address enterprise requirements, or the enterprise customer will be forced to take care of the problem on their own.