About SITI, SOTO and such.
A ticket LHR-ORD-LHR issued in the UK is SITI.
The same ticket sold in Hongkong would be SOTO.
Generally in this example the pax has no main differences, except he wants to stop over between LHR and ORD.
In this case he must pay a fare difference for a socalled HIP (Higher intermediate Point) for the SOTO, but not for the SITI ticket.