Question: What triggers the restart of the Tast timer in a network supporting A-interface link sharing for Voice Group Call Service (VGCS)?
Option 1: Receipt of a new group call setup request from the User Equipment (UE)
Option 2: Expiration of the Tast timer with no changes in Group Call Area cells since the last report
Option 3: Successful release of all channels in the Group Call Area
Option 4: Expiration of the Tast timer with changes in Group Call Area cells (e.g., new cells established, existing ones released, pre-empted, or failed)
Explanation: The correct answer is Option 4 because, according to the specifications for Voice Group Call Service (VGCS), the Tast timer is restarted after it expires if there have been changes in the Group Call Area cells (such as new establishments, releases, pre-emptions, or failures). This ensures the MSC is updated on these changes and then the cycle of measuring time until the next report begins again.