What is an area control centre?

-i am staying in trivandrum (southern part of india) and according to wikipedia trivandrum is an area control center .

suppose an international flight from australia to middle east is flying over trivandrum ,does that mean that the pilot has to report trivandrum air traffic controlller .what exactly is the function of an area control center



in international flights to whom all a pilot reports in the flight's route



are aircraft communications line of sight communications ,if it so then how air traffic control centers able to communicate with aircrafts which are hundreds of miles away?