Sourcing airfares for travel originating in one’s home market  is not as big a challenge as accessing  global airfares for travel originating in other countries.

For travel professionals whose business caters to travel originating from outside their home country, sourcing global airfares from varied source points requires major time and effort. This is the case if the inventory comes from  the airline, a GDS or a third party provider.

Read more here – http://www.tnooz.com/article/choosing-the-right-API-sourcing-global-airfares/