An airline reservation system (ARS) is part of so-called passenger service systems (PSS), which are applications that support direct contact with the passenger.
ARS eventually evolved into the computer reservation system (CRS). A computer reservation system is used for booking a particular airline and interacts with a global distribution system (GDS) that supports travel agencies and other distribution channels to make reservations for most major airlines in A single system.
The airline reservation system includes airline schedules, fares, passenger bookings and ticket registrations. The direct distribution of an airline operates within its own reservation system, in addition to sending information to the GDS. The second type of direct distribution channel is consumers using the Internet or mobile applications to make their own reservations. Travel agencies and other indirect distribution channels access the same GDS as those accessed by airline reservation systems, and all messages are transmitted by a standardized messaging system that operates on two types of messages transmitted on the HLN network Of SITA. These types of messages are called Type A [normally EDIFACT format] for real-time interactive communication and Type B [TTY] for information and reservation messages. The standards of message construction established by IATA and ICAO are global and apply to more than air transport. Since airline reservation systems are business-critical applications, and are functionally quite complex, the operation of an internal airline reservation system is relatively expensive.
Prior to deregulation, airlines had their own booking systems with the travel agencies that subscribed to them. Today, GDSs are run by independent companies with airlines and travel agencies as their main subscribers.
As of February 2009, there are only four GDS vendors in the market: Amadeus, Travelport (which operates the Apollo, Worldspan and Galileo systems), Saber and Shares. There is an important Regional GDS, Abacus, which serves the Asian market and several regional players serving isolated countries, including Travelsky (China), Infini and Axess (both from Japan) and Topas (South Korea). Of these, Infini is housed within the Saber complex, Axess is in the process of moving into a partition within the Worldspan complex, and Topas agencies will emigrate at Amadeus.
Booking systems such as Navitaire and Radixx International are "no-frills" and "hybrid" carriers (airlines using e-ticketing as well as tickets to accommodate code shares and interlines).
Radixx International is a hybrid travel distribution and PSS designed to enable airlines to increase revenue and profitability by expanding the distribution to sell through any channel, either ticket or no ticket.
In addition to these "standardized" GDSs, some airlines have proprietary versions that they use to run their flight operations. Some examples are the Deltamatic OSS system and EDS SHARES. SITA Reservations remains the largest multi-host airline reservation system with more than 100 airlines currently managing the inventory.
