Question: What happens to a ROUTING AREA UPDATE REQUEST message that fails the integrity check in the network?
Option 1: The network processes the request without any further action.
Option 2: The network initiates an re-authentication of the subscriber by initiating an authentication and ciphering procedure.
Option 3: The LLC layer in the network discards the message.
Option 4: The GMM entity in the network sends a DETACH ACCEPT message.
Explanation: According to the text, if a ROUTING AREA UPDATE REQUEST message fails the integrity check, the network shall initiate an re-authentication of the subscriber by initiating an authentication and ciphering procedure. This is because the message may have been sent with an UMTS security context that is no longer available in the network.