This Market Segment covers that wiring underneath travel. It has two parts:

It is a small Market Segment, with five companies. But two of them have some of the most job postings in this Industry Vertical. The travel sites on top of this wiring are covered in Market Segment 29.1, Online travel agencies (OTAs). The airlines' and hotels' own engineering centres in India are covered elsewhere.
Every company named here has posted software engineering jobs in India. Famous companies that don't actively hire software engineers in India are left out.
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Back to the flight to Goa from the start of this Market Segment. Here are the companies whose systems it passed through.
Travelport and TBO Tek are not covered in this Market Segment.
Airlines used to file their fares with the distribution systems, which showed the same fares to everyone. Now airlines are building their own offers and orders, priced for each customer. They sell them directly, or through agents. The distribution systems are rebuilding themselves around this change. Much of the software for it is written in Bengaluru and Pune.

Who these companies hire, and for what, is on What travel tech companies hire for.