When you want to pair up Desktop and Mobile Softphones where the Desktop calls route to the PSTN SIP trunks and the Mobile Calls via the Internet, how are calls routed to both the devices to ring simultaneously.
a) Is the routing handled by the router or Firewall through separate Ports
b) should it be configured at ISP Firewall or the Customer Firewall
b) do you need to assign separate Public Addresses for the SIP Trunk and Internet Gateway
b) do you need an SBC ( session border controller) installed