The present document gives a general description of a GSM Public Land Mobile Network (PLMN). It contains a definition and a summarised description of the elements comprised in the network, and their functions and the associated performance objectives. The services and facilities that the network can offer to its users, are also described as well as the general lines of signalling procedures, operation and maintenance. Since the present document includes information spread throughout all GSM specifications this document can serve as guide. The terms GSM MoU and PCN MoU (or sometimes MoU only) used in this document refers to Operators organisations implementing GSM and to which some responsibility of referred-to documents belong.