A mobile switching center (MSC) is the central component of a network switching subsystem (NSS), which facilitates the switching of calls between mobile users and other fixed or mobile network users. The functionalities of an MSC include access and mobility management, call handling (such as call set-up, release, and routing), routing SMS messages, managing conference calls, fax services, service billing, and interfacing with other networks. Viettel MSC supports all functions of an MSC/GMSC and serves 2G/3G/4G (CSFB) subscribers.