Callers make initial contact through the 999 emergency telephone service, where their calls are answered at an operator assistance centre (OAC).
Prior to this time there were assorted basic means of communication with centralised control, including operations rooms with telephones, maps, direct lines to police boxes, and radios.
Emergency control centres are open twenty-four hours a day, all year round, and are usually busiest on Friday and Saturday nights.
Being staffed twenty-four hours a day requires large numbers of staff, typically around 80 operators in an average size jurisdiction.
Even though the number "100" is primarily meant for informing or help by police, common people of India use it for many purposes including help during disasters, traffic jams, counselling among others.