Question: In an SDP offer/answer transaction for IMS, what is the primary purpose of including a 'visited realm instance' for each media line by an OMR-capable entity?
Option 1: To advertise available transcoding options for subsequent media path segments.
Option 2: To ensure backward compatibility with non-OMR capable entities.
Option 3: To provide connection information matching the media line in the forwarded SDP offer, enabling detection of intermediate codec changes without altering connection and port details.
Option 4: To reserve specific IPv4 addresses for networks with private reachability.
Explanation: The correct answer highlights the key function of a 'visited realm instance' in SDP transactions, ensuring detection of intermediate codec changes without altering connection and port details, thus maintaining media path setup integrity.