Whenever a passenger books an itinerary, the travel agent creates a PNR in the Computer Reservation System used by the airline or railway company through company’s website.At this stage of booking, the CRS will generate an alpha-numeric record locator that remains the same irrespective of any further changes. This record locator is used for identifying PNR in the particular database.
On booking of an airline ticket, every airline creates their own booking record along with a unique record locator that is transmitted to the CRS and gets stored in the database.
Indian Railways is the world’s largest issues of PNR Numbers in a single day. It issued more than 200 million tickets in 2015 making it the single largest ticket issuing organisation in the world.