If the server was going down every 30mins, the forum would be absolutely flooded with posts about your server specifically — but it’s not.
Is every game you play hosted on Blizzard’s servers and in the same city? I doubt it. The internet is more complex than “I can connect to Final Fantasy, so I should be able to connect to everything on the internet!”
This misconception is too common. Blizzard even has a sticky thread about it:
Again, if you’re here to argue about the server, none of the players volunteering in this forum can help you. That’s right, players. This forum is supported by fellow players, not anyone paid by Blizzard. Good luck with your issue.