ITU-T Rec. Q.512 (1988)
1 General
2 Scope of Recommendation
3 Characteristics of digital exchange interfaces for subscriber access
3.1 General
3.2 Interface V1
3.3 Interface V2
3.4 Interface V3
3.5 Interface V4
4 Characteristics of analogue exchange interface for subscriber access
4.1 Interface Z
5 Combined digital and analogue interface for subscriber access