Question: What is the purpose of the AMF field in relation to the USIM's mechanism for limiting the amount of data protected by an access link key set?
Option 1: To increase the lifetime of cipher and integrity keys.
Option 2: To decrease the security level of the network authentication token.
Option 3: To adjust or set the threshold values that restrict the lifetime of cipher and integrity keys.
Option 4: To disable the USIM's mechanism for limiting the amount of data protected by an access link key set.
Explanation: The AMF field is used to instruct the USIM to switch between two threshold values, which are used to limit the amount of data that can be protected by an access link key set. This allows the operator to adjust or set these threshold values, thereby controlling the lifetime of cipher and integrity keys.