Airlines sell tickets via a number of distribution channels—for example, online websites, phone reservation centers, brick-and-mortar travel agencies, and online travel agencies. The Airlines Reporting Corporation (ARC) is one of two key entities that help streamline the ticketing process by acting as a link between passenger carriers (which includes airlines, railroads, etc.) and travel agencies. ARC is similar to the International Air Transport Association (IATA) in that it oversees the billing and settlement plan systems for both brick-and-mortar and online travel agencies. ARC is responsible for financial transactions in the United States, Puerto Rico, the U.S. Virgin Islands, and American Samoa. IATA is responsible for all other transactions.