Question: In a SIP-I based circuit-switched core network, when a user is on hold during the setup of a multi-party call, how are the Conference Setup Notification and Hold Retrieval signaled if sent separately?
Option 1: Both signals are encapsulated in separate SIP INFO messages.
Option 2: The Conference Setup Notification is sent via SIP INFO, while the Hold Retrieval is signaled through a standalone CPG message.
Option 3: The Hold Retrieval is encapsulated in a re-INVITE, and the Conference Setup Notification is sent as a response to the re-INVITE.
Option 4: The Conference Setup Notification is encapsulated in a SIP INFO, and the Hold Retrieval is encapsulated in a re-INVITE that activates the held media.
Explanation: According to the principles of managing multi-party calls in a SIP-I based circuit-switched core network, when signaling involves a user on hold, separate signals for conference setup notification and hold retrieval are handled distinctly. The Conference Setup Notification is appropriately sent via a SIP INFO to inform the user without immediately activating their media stream. Meanwhile, the Hold Retrieval, which aims to activate the held media, is effectively encapsulated within a re-INVITE message. This approach ensures that the user's media stream is properly activated as part of joining the multi-party call, while also keeping them informed about the conference setup through a separate, non-disruptive notification channel.