Fixed-mobile convergence—the ability for phone service to roam seamlessly between cellular and other voice networks—holds a lot of promise for carriers and consumers alike.

 

In the rush to stay competitive and roll out such services quickly, many carriers have chosen to use Unlicensed Mobile Access (UMA) technology to achieve fixed-mobile convergence deployments.

 

But, as Accuris Networks CTO Louis Corrigan recently told TMCnet, there’s a problem: “UMA wasn’t designed to be an enabler for fixed-mobile convergence.”

 

Corrigan, and Accuris CEO Aidan Dillon, recently spoke with TMCnet on the phone about the limitations of UMA and why carriers should be choosing IP Multimedia Subsystem (IMS) technology instead.

 

 

UMA, Corrigan told TMCnet, is a technology that came out of 3GPP, and can be used to turn WiFi (News - Alert) into an access medium for cellular. It does this by using protocols to create a cellular “tunnel” through WiFi.

 

Because it can be used with existing cellular infrastructure, UMA is appealing to carriers looking for a quick way to ramp up converged, fixed-mobile services.

 

UMA is a short-term solution, though, because it offers no integration with SIP, now the standard signaling protocol for most corporate voice networks and PBXs.

 

The result is that, while UMA lets individual customers to roam between cellular and home WiFi networks, that functionality isn’t interoperable with corporate networks.

 

“The technical scope of UMA is quite limited,” Corrigan said. Worse still: “UMA has no migration strategy.”

 

 

A much better choice of technology for carriers is IMS, which does offer integration with SIP and as such is a long-term investment.

 

Most U.S. telecoms, Corrigan said, accept that they’ll eventually need to deploy IMS networks. What many carriers don’t realize, though, is that they can begin investing in the future immediately by using some components of IMS to deliver SIP-enabled, converged, fixed-mobile services today.

 

“You don't have to have a full IMS network to introduce SIP,” Corrigan said.

 

Because IMS is compatible with SIP, it opens up new revenue streams for carriers, especially telecoms who may be able to lure subscribers away from their cellular providers.

 

Dillon added that IMS helps broaden revenue streams because it provides fixed-mobile convergence of all communications services, not just voice.

 

 

If IMS is so much better than UMA, the question begs to be asked: Why have so many carriers chosen the lesser technology?

 

Corrigan provided three main reasons:

 

1. IMS is becoming a commercially viable technology much faster than carriers anticipated; they chose UMA because it seemed the only option in the near future.

 

2. There is a misconception among many carriers that, to use IMS for fixed-mobile convergence, a complete IMS network has to be installed.

 

3. Carriers were concerned about the potential availability of handsets capable of delivering converged, fixed-mobile services.

 

The first point requires little comment; the second has already been discussed. That leaves handsets.

 

Although a few UMA-enabled handsets are now being manufactured, Corrigan said they are niche products and always will be.

 

Today, standard handsets are widely available that contain several access technologies, including WiFi, Corrigan said. Sold as commodities, these handsets can be used with IMS’s now-standard ability to perform handoff between WiFi and cellular networks.

 

IMS isn’t just the best technology for carriers; it also provides benefits to the end-user as well.

 

In the case of consumers, Dillon said, IMS makes possible a true convergence of IP-based services, including voice and TV. The result is more competition between carriers, and consumers win by having access to lower-cost services.

In the business-user segment of the industry, the benefit of SIP’s inclusion in IMS makes the comparison even more clear-cut.

 

“For corporate users, SIP will work and UMA won’t,” Corrigan said.