"As wireline and wireless operators are deciding to build out VoIP services using a call control layer with softswitch and media gateways, they are confronted with a choice between a traditional voice-oriented softswitch architecture or softswitch solutions that can be upgraded to support the IMS topology," said Bettina Tratz-Ryan, research director for Gartner. "Operators that want to emulate existing voice services on time division multiplexing (TDM) infrastructure and see voice as a discreet service will opt for established softswitch topologies. Operators comfortable with not having to offer all the legacy voice services and that see value in offering new value-added voice services will need to decide between an IMS upgradeable or IMS compliant solution."
Operators with a clear path to fixed-mobile convergence (FMC) and converged services across voice, video and data will be deploying horizontal session control architectures such as IMS. Wireline operators have taken the lead in deploying next-generation network (NGN) architectures that can benefit from IMS to realize operating expenditure savings and provide a basis for converged applications in the long run.
However, for operators implementing VoIP to emulate their existing voice services, deploying IMS will not offer material benefits over traditional softswitch-based architectures. The latter are less expensive and have been market tested. Most modern softswitches also have a migration plan to IMS.
For operators planning to offer value-added VoIP services, IMS delivers long-term core networking efficiencies. It also offers a standardized way of providing value-added voice applications, such as push-to-talk over cellular. This will lead to lower total cost of ownership and less vendor lock-in. But these advantages will take time to develop and are not expected within the next 24 months.