In TAF-TSI the communication between Applicant and IM is designed as the following:

• Applicant sends a PathRequestMessage that contains a path request (PR) in the PathInformation element and additional information about the train run (TR) in the TrainInformation element. The connection is set between the PR and TR using identifiers.
• Then, the IM sends back PathDetailsMessage(s) with the path(s) (PA) that are linked to the previously received PR and TR objects.

However, in PCS, the full journey of a train is prepared in one dossier (the base entity of the system, also known as “Case Reference” in TAF TSI) containing more than one path request and more than one path if more than one applicant and/or Infrastructure Manager. The harmonization happens on the dossier level among the territories (Applicant – IM pair) and not on the PR/PA level. In order to enable this harmonisation, a specific logic with the TAF-TSI messages is applied with the PathCoordinationMessage for dossier promotion and harmonization status.

In addition, coordination between timetables is required, especially at border locations.  Applicants and IMs need to update their PR/PA objects (see here for more details) before submitting a path request or an offer. The PR/PA objects update also relies on the PathCoordinationMessage.