Even with all the talk about IMS networks, the VOIP softswitch still has a big future.

That's one of the findings of a new Heavy Reading report, "IMS & the Future of Softswitches in Next-Gen Networks."

The main reason softswitches will be around for awhile is that many carriers aren't moving very quickly toward IP Multimedia Subsystem (IMS), says John Longo, the Heavy Reading analyst who authored the report. In IMS networks, he explains, the traditional functions of the softswitch are distributed to other network elements. (See Is the IMS Honeymoon Over? and A Big Softswitch Surprise.)

"My notion coming into the report was that we're starting out with all this movement toward IMS and next-generation networks, and we wanted to see if the softswitch was dead or if it at least has a limited life," Longo tells Light Reading. "My analysis is that there's a lot of life left in softswitches -- in fact, they’re going to grow for awhile." (See Sonus Touts Growth.)

Longo says 44 percent of the carriers he surveyed for the report are not now evolving their networks toward IMS. Another 7 percent say they have no plans to do so. Of the five service providers Longo interviewed and profiled in the report, only AT&T Inc. (NYSE: T) reports moving aggressively to implement IMS.

"You have the Big Kahuna AT&T going the IMS route; all the others are on the sidelines saying, 'We don't really see a need right now,' " Longo says. "So I think there are a lot of folks asking, 'Do I really need to do this?' " (See Quigley: IMS Won't Cure All.)

Some carriers are forced to leave the TDM world, yet aren't ready to step into the IMS world. Longo cites examples where the carrier is using old digital switches that are no longer supported by the vendor. If that carrier sees no immediate need to move to IMS, the best move is to replace the old switches with softswitches.

"The original softswitches had all the functions that the old TDM switches had -- they just did them with IP." With the arrival of IMS, switch functions like signaling and media gateway functions, subscriber data management, and call agent functions begin to be distributed into other network elements in the IMS architecture, Longo says. If carriers continue their embrace of IMS as the way of the future, the softswitch as we know it today could eventually go away.

But even carriers (like AT&T) that are very committed to IMS won't rip out their softswitches right away. Carriers will leave them in place as the IMS network develops and because the softswitches haven't reached end-of-life.

"Of those carriers considering IMS networks, about half of them believe that softswitches will coexist with IMS," Longo says. In that scenario, the traditional call switching functions would remain contained in the softswitch. Whether or not to distribute those functions out to other IMS network elements would be up to the carrier.

Longo points out that IMS specifies a set of functions to be carried out by the network, but does not specify the actual devices that complete those functions. It's up to the carrier's engineers to decide how best to leverage softswitches as IMS begins to govern the shape of their networks.

For more information on the report, click here.

— Mark Sullivan, Reporter, Light Reading