Question: In an IMS centralized services architecture, what security mechanism is specified for protecting the I2 reference point between the MSC server enhanced for ICS, unless the control plane interfaces are trusted?
Option 1: Network Domain Security/IP (NDS/IP) according to security standards
Option 2: Transport Layer Security (TLS) for all IP connections
Option 3: Diameter Encryption for all control plane messages
Option 4: Secure Sockets Layer (SSL) for I2 reference point only
Explanation: NDS/IP is the specified security mechanism for protecting the network domain, including the I2 reference point in IMS architectures, unless trusted interfaces negate the need for such protection, ensuring secure communication across potentially vulnerable IP networks.