5 High level functionality and features

6 Functional description and information flows

4.2.4 Service-based interfaces

4.2.3 Reference points

4.2.3 Inter-PLMN reference architecture

4.2 Architectural reference model

4.2.2 Roaming reference architecture

4.2.1 Non-roaming reference architecture

4.1 General concept

3 Definitions of terms and abbreviations