I believe those have something to do with hooking into a sattalitte system for information, computers, something like that. I can fully agree its not really a good answer, but I guess it's a start right.
They were big because they were for sending not just getting. I think Hazmat might have them as a backup. This was before NycWin was installed in the city, now most IP data traffic will go over that system. However they will keep some SAT stuff as backup just not using it routinly.