The PRS-CSI is an interface between a single remote call station, PRS-CSR, or a remote call station kit, PRS-CSRK, and the fiber optical Praesideo network. It uses CAT-5 cable for the connection to the remote call station. The CAT-5 cable, carrying digital audio and control data, can be as long as 1 km. The length of the CAT-5 cable is not a part of the Praesideo optical network length. This considerably increases the overall possible length of the optical network, especially in cases, where the call station is located far from the rest of the system.