3.9.5.2.2.4 Ringing Private Line
This section follows the product behavior described in endnote <58>.
If the incoming INVITE is targeted at the private line of the user, the call MUST be forked to the registered endpoints whose address-of-record matches the address-of-record of the target. In addition, if the simultaneous_ring flag is set, the INVITE MUST be routed to the target specified in the simultaneous_ring list. The proxy MUST then start the registered endpoints timer.