Question: In IMS (IP Multimedia Subsystem) for calls originating from the PSTN (Public Switched Telephone Network), what action does the MGCF (Media Gateway Control Function) take regarding the calling name when inserting an asserted identity into a SIP (Session Initiation Protocol) message?
Option 1: The MGCF always inserts a default calling name if the incoming information from the PSTN lacks it.
Option 2: The MGCF never includes the calling name in the SIP message for privacy reasons.
Option 3: The MGCF only inserts the calling name if explicitly requested by the originating party.
Option 4: The MGCF may insert the calling name into the display name portion of the asserted identity if available from the PSTN or obtainable.
Explanation: This is correct because, according to procedures for providing the authenticated identity of the originating party in PSTN origination, the MGCF has flexibility to include the calling name in the SIP message's display name portion if such information is either directly received from the PSTN or can be obtained, balancing caller identification needs with available data constraints.