Question: What is the required format for the host portion of the Default Conference Factory URI for MMTel, based on a User Equipment's (UE) home network domain name?
Option 1: The UE's phone number prefixed with "conf-factory."
Option 2: The home network domain name prefixed with "conf-factory."
Option 3: A random generated string to ensure uniqueness
Option 4: The UE's IP address converted to a domain name
Explanation: According to telecom standards for MMTel (Multimedia Telephony) services, the Default Conference Factory URI is formatted as a SIP URI. To maintain consistency and proper routing, the host portion of this URI must be set to the UE's home network domain name, with "conf-factory." prepended to it. This ensures that conference invitations are correctly directed within the user's home network for processing and setup.