What would happen if a major terrorist attack struck your city?

Be it Dublin, Cork, wherever.

We know from some very old news articles that Ireland has an Emergency plan to deal with a nuclear attack, but we don't seem to know what's in it.

Imagine all all of the main communication modes (TV, radio, internet and phones) are down, either because of the attack or because of congestion. How difficult would that be to do? (neither asking for myself nor for a friend). That would mean no system in place for us to know what is happening via our smartphones, and maybe laptops or even radios. I'm not even sure the Luas or the Dart would work.

I started thinking about this because I was waiting for the Luas yesterday, and there was a public service announcement. That's a good way to reach a large number of Dublin's citizens, anyway. Dart-station announcements are another (presumably, if they worked, they'd tell people where to take shelter -- but do we even have working shelters? I only know of one, built for the Government in Merrion Square Park, and it is probably now redundant. )

Does Ireland, in general, have a plan in order to communicate with large volumes of people? Do the radio and TV stations have plans for this?

In Dublin, of all places, we know how crucial communication hubs can be to terrorist attacks -- after all, it was the GPO, the main information exchange of its day, which was the epicentre of the Easter Rising.

I am not a paranoid person, but I do think it's only a matter of time before terrorists, of whatever bent or hue, become sufficiently sophisticated to attempt a systematic attack on communications and then on individuals. Dublin will hardly be a target, nor any Irish city including Belfast, but still, it's useful to consider how prepared we might be, and what might be our weaknesses.