network subsystem (mobile communications) (NSS)
InGSM networks, network subsystems( NSS), also known as switching subsystems( SSS), perform the switching tasks, which include switching the radio channels to fixed networks. The central unit that performs these nodal functions is the mobile switching center( MSC). The mobile switching center supports various services for data transmission and the short message serviceSMS, as well as routing from third-party networks to the mobile station.
Part of the NSS system are the databases for the location directory( HLR) and for the visitor directory( VLR).