Yesterday, Delta finally implemented something called "Journey Control technology".

This new automation, which most other carriers already have in place, will prevent booking one flight segment at a time for any reservation that requires a connection in the same booking class to the final destination.

In the past, one was able to book point to point - thus circumventing the availability which is based on Origin and Destination.

The new technology will review each new booking and itinerary change to ensure compliance with O&D guidelines. Bookings or cancellations which violate Journey Control rules will receive a unique error message denying the transaction.

Most likely, this will also change the way upgrades will be assigned...