TThe purpose of this third edition European Telecommunication Standard (ETS) is to present the possible architectures of the mobile system. Clause 3 of this ETS contains a definition of the different functional entities needed to support the mobile service. In clause 4, the confi guration of a PLMN is described as well as the organization of the fun ctional entities; the configuration presented is the most general in o rder to cope with all the possible implementations which can be imagin ed in the different countries. To illustrate that purpose, some exampl es of possible configurations are presented. Clause 5 of this ETS cont ains a brief description of the interfaces involved which shows the pr inciple of the organization considered.