When you have a fire alarm system in a commercial building, are you required to have a central monitoring service subscription or does the fire alarm system call the fire department directly?

I am not an alarm installer and I don't want to be one, just curious how this works.

Most fire department don't receive alarms directly these days; alarms are monitored by the alarm company.

Almost all of the direct alarm lines 'BANA circuits' have been ripped out around here.
2 POTS lines to the fire panel is the norm.