Question: What is the primary purpose of the bootstrapping transaction identifier sent by the Bootstrapping Server Function (BSF) to the User Equipment (UE)?
Option 1: To initiate a new authentication protocol between the BSF and UE.
Option 2: To notify the UE about the key lifetime expiration.
Option 3: To establish a secure tunnel for subsequent communications.
Option 4: To uniquely identify the bootstrapping session for shared key establishment.
Explanation: The correct answer is Option 4 because, in the context of Generic Bootstrapping Architecture (GBA), sending a bootstrapping transaction identifier is crucial for identifying and managing the specific bootstrapping session between the BSF and UE. This identifier ensures that both parties are aware of the context in which the shared keys are established, thus facilitating secure communication. While key lifetime notification is also a requirement, it is not the primary purpose of the transaction identifier itself. Options 1 and 3, although related to security protocols and communications, do not accurately describe the main function of the bootstrapping transaction identifier in this context.