Evolution from Fixed Softswitch to IP Multimedia Subsystem

The evolution from fixed Softswitch to IP Multimedia Subsystem (IMS) requires reasonable methods, steps and strategies. IMS as a smooth evolution can preserve the Softswitch-based PSTN Emulation Subsystem (PES), and realize Fixed and Mobile Convergence (FMC) at the core with the introduction an proliferation of multimedia and mobile services. Therefore, Softswitch as the core control layer of Next Generation Network (NGN) is not contradictory with IMS as it can be mapped into the IMS architecture. While Softswitch can provide PSTN emulation services, IMS mainly designed for FMC and multimedia services is capable of supporting mobility, security, QoS and open services architecture. The evolution from Softswitch to IMS is technologically feasible. For operators who have already adopted Softswitch technology, they can evolve their networks to IMS-based full-service NGN, to reduce their investments, risks of network modification, and operational costs.