CCITT Rec. I.320 (11/1988) – ISDN PROTOCOL REFERENCE MODEL
1 Introduction
2 Modelling concepts
    2.1 Relationship with the X.200-Series
    2.2 Control and user planes
    2.3 Local and global significance
3 Model
    3.1 Generic protocol block
    3.2 Relations between layers in one plane
    3.3 Relations between planes
    3.4 Data flow modelling
4 ISDN management
5 Interworking
    5.1 General
    5.2 Relationships with the OSI RM
6 Examples
    6.1 Basic call situations (no supplementary service, no interworking)
    6.2 More elaborate situations
    6.3 Interworking