Question: What protocol is optionally used for IOPS-related signaling (e.g., discovery, subscription, and notification events) over the MC-IOPS-X1 reference point in Isolated Operation for Public Safety (IOPS) mode?
Option 1: Diameter Protocol
Option 2: Session Initiation Protocol (SIP)
Option 3: HTTP/2
Option 4: SS7 (Signaling System No. 7)
Explanation: In the context of IOPS mode, for efficient and standardized signaling related to events like discovery, subscription, and notification, SIP is noted as a viable option for IOPS-related application signaling over the MC-IOPS-X1 reference point. This is because SIP is widely used for managing communication sessions in IP networks, making it suitable for such transactions in IOPS scenarios where the signalling application server and client interact as SIP entities.