Telstrat Argent - Manual (Page 24)

Argent Terminal Adaptor - User Guide
Version 1.1 Telstra Corporation Limited
Page 24/29 ACN 051 775 556
5.1.1 Abbreviations used in the POTS feature descriptions
[...] Square brackets indicate that the enclosed item is optional
DN Destination number
DT Dial Tone
OH Off Hook
RH Replace Handset when condition detected by ATA
RR Recall signal from telephone
RSP Network Responds with confirmation tone