Question: Which of the following is NOT a mandatory capability supported by the Iu interface?
Option 1: Procedures to establish, maintain, and release Radio Access Bearers
Option 2: Mechanisms for resource reservation for packet data streams
Option 3: Transfer of NAS signalling messages between UE (User Equipment) and CN (Core Network)
Option 4: Mechanisms to support SIPTO at the Local Network with standalone GW for a specific UE
Explanation: The correct answer is Option 4 because it is implied as optional, unlike the other options which are standard capabilities supported by the Iu interface. Support for Option 4 is not mandatory for all implementations.