Question: In IMS (IP Multimedia Subsystem), when an Application Server (AS) interacts with a Media Resource Function Controller (MRFC) for services like multiparty sessions, which two approaches can the AS use to control the sessions?
Option 1: SIP MESSAGE method and HTTP POST
Option 2: 3rd party call control and the SIP REFER method
Option 3: SDP Offer/Answer and DNS NAPTR
Option 4: TLS Tunneling and XML Configuration
Explanation: In IMS, an Application Server (AS) interacting with a Media Resource Function Controller (MRFC) for advanced services uses specific SIP-based mechanisms. The two approaches are: 3rd party call control, allowing the AS to manage calls on behalf of another party for multiparty sessions or invocation of services; and the SIP REFER method, enabling the AS to request the MRFC take over a session, facilitating transfer of session control for capabilities like multi-party conferencing.