�1���� Scope
�2����
References
�3����
Definitions
�4����
Abbreviations
�5����
Protocol stack and system models
������� 5.1���� Protocol stack model
������� 5.2���� System model/overview
�6����
Interaction channel for PSTN
������� 6.1���� PSTN requirement
������� 6.2���� PSTN interfaces requirement
�7����
Interaction channel for ISDN
������� 7.1���� ISDN requirement
������� 7.2���� ISDN interfaces requirement