While in Survivability Mode, SIP-to-SIP calls within the same BG (Business Group) are possible by dialing the extension number. SIP-to-SIP calls to another BG are accomplished by dialing the Directory Number (DN) of the destination phone.
On SIP to SIP calls between different BGs the SIP gateway handles calls locally and reroutes calls to the local gateway or local EP (Endpoint). The SIP gateway adds or strips off leading access code digits.
Parent topic: Survivability Overview
RG 8700 SMG (Survivable Media Gateways)