A Remote Worker Using the Avaya Equinox on the Smart

A remote worker using the Avaya Equinox on the smart mobile telephone obtains a private IP address delivered from the corporate network over WiFi when in range of the wireless hotspot. When the remote worker is out of range of the corporate WiFi it obtains a Public IP address via the 3G/4G mobile Service Provider. When roaming from the public network to the corporate private network and vice versa, which strategy prevents the user from having to change the SIP Proxy Server address in the smartphone?

A) Virtual Private Network (VPN)
B) Split Horizon DNS with FQDN
C) Avaya Session Border Controller for Enterprise (SBCE) public IP-address
D) Network Address Translation (NAT)