网络交换子系统（Network Switching Subsystem，简称：NSS）又称GSM核心网（GSM Core Network），是GSM系统的一个组件，它为基站网络上的移动电话漫游（mobile phones roaming）实现电话交换（call switching）和移动性管理（mobility management）功能。它为移动电话运营商（mobile phone operators）所拥有并部署，允许移动设备与各个其它的电话，在更为广泛的公共交换电话网（PSTN）中进行通信。该架构包含一些因为电话并非固定在一处，因而必须具有的特定的特性和功能。

Network switching subsystem (NSS) (or GSM core network) is the component of a GSM system that carries out call switching and mobility management functions for mobile phones roaming on the network of base stations. It is owned and deployed by mobile phone operators and allows mobile devices to communicate with each other and telephones in the wider public switched telephone network (PSTN). The architecture contains specific features and functions which are needed because the phones are not fixed in one location.