ion SBC Destination SBC Destination SBC Destination SBC sends 200 OK sends 200 OK with sends 200 OK with sends 200 OK sends 200 OK sends 200 OK with sends 200 OK with sends 200 OK with IPv6 ANAT information- ANAT information- with IPv6 with IPv6 ANAT information- ANAT information- with IPv6 information IPv6 priority IPv4 priority information information IPv4 priority IPv6 priority information Originating SBC Originating SBC Policy: sends ACK with sends ACK with TPV6 promotion IPv6 information Policy: Policy: Policy: Policy: IPv4 information towards destination omotion Policy IP version towards destination Originating SBC sends IP version SBC and 200 OK IP version IPv6 promotion ACK with IPv6 information coherence SBC and 200 OK coherence with IPv4 coherence with IPv4 towards destination SBC information towards Originating SBC sends ACK with IPv6 information towards information towards destination SBC and and 200 OK with IPv4 calling IPv4-only calling Dual-stack 200 OK with IPv6 information towards information towards calling IPv4-only UA Originating SBC sends ACK with IPv6 Originating SBC sends ACK with IPv6 calling dual-stack UA information towards destination SBC and information towards destination SBC and 200 OK with IPv4 information towards 200 OK with IPv4 information towards calling IPv4-only UA calling IPv4-only UA Destination SBC Destination SBC Destination SBC Destination SBC sends ACK with sends ACK with sends ACK with sends ACK with IPv6 information to IPv4 information to IPv6 information to IPv6 information to called UA called UA called UA called UA Mixed media IPv4 media IPv4 media IPv6 media Mixed media exchanges exchanges exchanges exchanges exchanges Considered as a new offer Considered as a new offer FIGURE 3.4 Blank SDP procedure applied for Alternative 2. C 2009 by Taylor & Francis Group, LLC Legend IPv4-only Type of the caller Dual-stack Caller side Callee side Policy: IP version Originating SBC sends Originating SBC sends coherence invite with empty SDp invite with empty SDP Control operation