Abstract: A small-capacity IMS core is a system that provides support so that a group customer using an IMS service can manage a POTS system and an Internet telephone system in parallel and can manage a non-IMS terminal. This system includes a main control unit (MCU) configured to provide only functions that belong to the functions of an MCU IMS structure and that are required for a group customer, a line interface unit (LIU) configured to be used to extend physical ports of the MCU and a POTS, a SIP gateway configured to convert a standard SIP message into an IMS message, and an FMC controller configured to provide support in order to enable a wireless terminal, such as a wireless IMS terminal/smartphone, to be used in a mobile environment. This system includes an IP communication-based virtual Ethernet back-plane so that the units can exchange information at high speed.