Design and Experiment of NFV-Based Virtualized IP Multimedia Subsystem

IP multimedia subsystem (IMS) has been recognized as the core control platform for the next generation network (NGN). In this paper, we focus on virtualizing IMS by enabling network function virtualization (NFV). NFV virtualizes network functions into software applications. The virtualized network functions can be decomposed into smaller functional blocks which will enable a high level of elasticity. This paper proposes an NFV-based virtualized IMS (vIMS) architecture that decomposes the S-CSCF into two key functions: one handles the UE registration (registration; R) and the other processes the call control (call control; C). Then the original I-CSCF is combined with the registration function (R), denoted by vI-CSCF(R). The S-CSCF reserves the call control function (C) only, denoted by vS-CSCF(C). We also design the registration procedure and call setup procedure in the vIMS. The vI-CSCF(R) is responsible for the original I-CSCF function and UE registration; thus, the vS-CSCF(C) is offloaded without handling any UE registration message. In addition, we analyze the queuing delay time of registration and call setup in the NFV-based vIMS architecture. Compared with the straightforward solution for IMS virtualization, our proposed vIMS has shorter delay time of registration and call setup by improving the S-CSCF's performance. In order to verify the feasibility of our proposal, we developed and deployed our proposed vIMS and the Clearwater-vIMS with OpenStack and Clearwater software, and run the stress test on them respectively. Compared to the original Clearwater-vIMS, our proposed vIMS have higher registration success rate and call setup success rate.