In a recent survey conducted by Heavy Reading, we asked respondents an open-ended question: Which softswitch vendors do you consider to be market leaders? Open-ended questions are very useful survey tools in that they enable greater variation in response and don't predispose survey participants to certain responses. But they can also be somewhat challenging to interpret when the results are surprising, as I learned with this survey.

The nearly 150 service provider professionals who participated in our survey named dozens of companies, some of which were unexpected. Included in the list of cited softswitch leaders were two IP Centrex/hosted PBX feature server companies, two session border controller (SBC) companies, and an open-source PBX company. Furthermore, one of the feature server companies was tied for first place as a softswitch leader!

The survey was conducted as a part of Heavy Reading's latest report, IMS & the Future of Softswitches in Next-Gen Networks. The report tracks the evolution of the softswitch, which is now devolving into its functional components as networks evolve to IMS and next-generation architectures. IMS is well known for introducing the layered approach to networking, with applications sitting on the top layer in the service or application plane; call control sitting in the middle in the control or signaling plane; and media riding in the bottom in the user or transport plane.

So why did survey participants list feature server and SBC companies as softswitch leaders?

During one of the in-depth discussions I had with service providers on their softswitch and IMS implementation plans, one source told me his company was using BroadSoft Inc. (a feature server) for its softswitch. I probed further at the time and learned that the company was using the BroadSoft platform to provide call control for its SIP-based VOIP calls. To be fair, the company was in the process of evaluating softswitches as well to expand its VOIP service, but the current service was provided via its BroadSoft platform.

Another hosted VOIP service provider did not employ any softswitches in its network. Carriers that receive only VOIP traffic do not need media gateways. SBCs serve as the network's edge device, and a call agent and routing engine provide the call processing for the network. For example, NexTone Communications Inc. 's Session Manager provides such a capability for its SBCs.

While many carriers are implementing IMS, at least as many are sitting on the sidelines waiting to see if they need all that IMS proposes to offer. And while IMS neatly lays out an architecture in which call control occurs in the middle layer, our research shows that not all carriers are managing their sessions and controlling their calls in the same place. In fact, different sessions may be managed in different parts of the network. For example, business customer calls may be handled very well by the hosted PBX feature server and do not need to be passed to a softswitch or the IMS core. Similarly, routing of intercarrier calls may occur at the edge of some networks, where the session manager and SBC have the most current information on route performance and availability.

So while the results to our open-ended question on softswitches may have been a bit surprising, the question did indeed provide very rich information that identified a trend that might not have been otherwise obvious. And, while IMS and next-gen networks clearly identify call control in the core of the network, our results suggest that call control and session management may and will occur in any of a number of places in converged IP networks.

— John Longo, Senior Analyst, Heavy Reading