The purpose of this specification is to identify the Interworking Functions (IWF s) and requirements for the interworking between a GSM PLMN and a PSPDN/ISDN for the support of packet services in GSM PLMNs. In the GSM PLMN context the packet services are associated with bearer services and are described in GSM 02.02. The generally defined GSM PLM user-network access as defined in the respective GSM TSs (see references) forms the basis for defining the particularities for the provision of packet services to the GSM PLMN subscribers. Network internal interfaces for the support of packet services in the pan-European ISDN are defined in ETSI standards, which are also taken as a basis. User-network access and network internal interfaces are defined to provide the packet services.