Rec. ITU-T X.2 (03/1993) INTERNATIONAL DATA TRANSMISSION SERVICES AND OPTIONAL USER FACILITIES IN PUBLIC DATA ...
FOREWORD
1 Introduction
2 Circuit switched data transmission service
3 Packet switched data transmission services
    3.1 Dedicated connection to a packet switched data transmission service
    3.2 Switched connection to a packet switched data transmission service (user classes of service 20-26 and 29)
    3.3 Switched connection to a packet switched data transmission service (classes of service 8-12, 26 and 30)
4 Leased circuit data transmission services
Appendix I
Appendix II
Appendix III Relationship of ISDN (I.25x) Supplementary Services and X.2 Optional User Facilities
III.1 Introduction
III.2 Independent operation
III.3 Minimum relationship
III.4 Maximum relationship
III.5 Summary