Question: In an IP Multimedia Subsystem (IMS), when a User Equipment (UE) registers with an IPv4 or IPv6 address, what is expected of the network design if the P-CSCF and IMS-AGW do not support both IP versions?
Option 1: The UE will automatically switch to the supported IP version.
Option 2: Communication with the IMS will only be possible via a third-party gateway.
Option 3: Network design must ensure IP address incompatibility does not occur, potentially through dedicated routing or translation mechanisms.
Option 4: The P-CSCF and IMS-AGW will always support both IP versions by default.
Explanation: This is because, as stated, if the P-CSCF (Proxy-Call Session Control Function) and IMS-AGW (IMS Access Gateway) do not support both IPv4 and IPv6, the onus falls on the network design to prevent any incompatibility issues that might arise from differing IP versions. This would typically involve implementing specific network configurations or mechanisms (like dedicated routing or translation services) to ensure seamless communication between elements of the IMS, regardless of the IP version used by the UE.