Question: In the context of IPsec for IMS (IP Multimedia Subsystem) as per 3GPP security specifications, what is the default IPsec protocol used if no Protocol parameter is present in the sec-mechanism agreement?
Option 1: AH (Authentication Header)
Option 2: ESP (Encapsulating Security Payload)
Option 3: Both AH and ESP are equally valid defaults
Option 4: It depends on the mode (trans or tun) specified
Explanation: According to the specifications, if no Protocol parameter is present, the value will default to ESP (Encapsulating Security Payload), aligning with the requirement for secure communication in IP-based services, where ESP provides both authentication and encryption.