Once the mission starts, you have to eliminate all enemies in the restricted area. You can snipe them from a distance to make your job easier. Once the enemies in the area are eliminated, you have to defend yourself from the incoming reinforcements.
You can destroy one enemy vehicle by blowing up the steam pipe nearby. Eliminate the remaining enemy forces. Take note that one of them may call additional reinforcements so you have to kill him quickly or just simply use Jam Coms to block the signal. After killing all enemies, head to the rooftop to reach Jacks. After the scene, the mission will be complete.