Question: What action does the Mobile Station (MS) take with regards to the old P-TMSI signature if no new P-TMSI signature is present in the P-TMSI REALLOCATION COMMAND message?
Option 1: The MS deletes the old P-TMSI signature.
Option 2: The MS keeps the old P-TMSI signature, if available.
Option 3: The MS updates the old P-TMSI signature with a new value.
Option 4: The MS ignores the old P-TMSI signature.
Explanation: According to the specification, if no P-TMSI signature is present in the P-TMSI REALLOCATION COMMAND message, the old P-TMSI signature, if available, shall be kept. This ensures that the MS retains the existing P-TMSI signature until a new one is provided.