An ISP my friend worked at was having weird outages in one area, and it turned out that they had an apartment block built right in the way of their free-space o

An ISP my friend worked at was having weird outages in one area, and it turned out that they had an apartment block built right in the way of their free-space optical link. Surprisingly, it was fine at first because the link went straight through it without obstructions, window to window. But when they started to add window panes, finishing the construction, the link became spotty, and adding the doors blocked the signal completely.