Question: What happens to the integrity protection of signaling messages during an intersystem handover from UTRAN to GSM BSS?
Option 1: It continues uninterrupted.
Option 2: It is stopped at handover.
Option 3: It is temporarily suspended and then resumed after handover.
Option 4: It is upgraded to a higher level of protection.
Explanation: During an intersystem handover from UTRAN to GSM BSS, the integrity protection of signaling messages is stopped at handover. This is because the handover implies a change in the ciphering algorithm and the GSM BSS does not support the same level of integrity protection as the UTRAN.