  Network functions virtualization provides opportunities to design, deploy,
and manage networking services. It utilizes cloud computing virtualization
services that run on high-volume servers, switches, and storage hardware to
virtualize network functions. Virtualization techniques can be used in IP
multimedia subsystem (IMS) cloud computing to develop different networking
functions (e.g., load balancing and call admission control). IMS network
signaling happens through session initiation protocol (SIP). An open issue is
the control of overload that occurs when an SIP server lacks sufficient CPU and
memory resources to process all messages. This paper proposes a virtual load
balanced call admission controller (VLB-CAC) for the cloud-hosted SIP servers.
VLB-CAC determines the optimal call admission rates and signaling paths for
admitted calls along with the optimal allocation of CPU and memory resources of
the SIP servers. This optimal solution is derived through a new linear
programming model. This model requires some critical information of SIP servers
as input. Further, VLB-CAC is equipped with an autoscaler to overcome resource
limitations. The proposed scheme is implemented in smart applications on
virtual infrastructure (SAVI) which serves as a virtual testbed. An assessment
of the numerical and experimental results demonstrates the efficiency of the
proposed work.
