NSS consists of the Mobile Switching Center (MSC) and the Visitor Location Register (VLR). A MSC manages multiple BSSs and is responsible for setting up, managing and shutting down connections,handling call chargessupervising supplementary services, such as call forwarding, call blocking and conference calling. 

VLR contains information about all MSs currently within range of the associated MSC. This information is needed for routing a call to a particular MS (mobile telephone) via the proper BSS and radio cell. The VLR also maintains a list of MSs belonging to subscribers of other GSM networks. Such subscribers have logged or roamed into the network of the associated MSC. The area covered by a MSC is actually called a MSC/VLR Service Area , which can consist of several LAs