Question: What is the purpose of the THRESHOLD value set by the operator and stored in the USIM?
Option 1: To limit the number of RRC connections that can be established.
Option 2: To ensure that a particular cipher/integrity key set is not used for an unlimited period of time.
Option 3: To trigger the generation of a new access link key set after a certain number of power cycles.
Option 4: To limit the amount of data that can be transmitted over a single RRC connection.
Explanation: The THRESHOLD value is used to ensure that a particular cipher/integrity key set is not reused beyond a certain limit, preventing attacks using compromised keys. This mechanism is necessary because authentication and key agreement are not mandatory at call setup, allowing for the possibility of unlimited and malicious re-use of compromised keys.