The MSS (also termed MSC-S) is a term used to describe the call control and mobility management aspects of a distributed switch (a Soft Switch), interfacing the GERAN/UTRAN to the CS domain. From a control perspective, the MSC-S has the same responsibilities as a regular telephony exchange, with the addition of user location registration and handover management. An MSC-S will control one or more CS-MGW (Circuit Switched – Media Gateways). An MSC-S may function as a GMSC (Gateway MSC), which is the term given to an MSC which handles mobile terminated calls originating in an external network. For example, exchanges in the PSTN are unable to interrogate the HLR therefore the call is routed to the GMSC in order to assist onward routing.