Understanding the various settings needed to properly configure Survivable Remote Gateway (SRG) requires an understanding of how SRG works and the overall SRG architecture.
Please review the following section of the E-MetroTel documentation for a full description of SRG functionality:
Survivable Remote Gateway (SRG)
For a description of the specific fields in the PBX / Settings / Survivability Settings page, refer to the following document: