Book 4 of the Corridor Information Document (CID) describes all customer relevant conditions and processes for booking and allocation of the PaPs and RC via the C-OSS supported by the IT tool PCS. 
The national network statements of the involved infrastructure managers - whereas serving as a legal basis for the PaPs and RC path usage contracts - refer to the Book 4 CID accordingly.

More details can be found here:

CID Book 4 Book Procedures for Capacity TT 2018