The PRS-CSR is a call station with the same functionality as the basic call station, LBB 4430/00, but it uses CAT-5 cable for its connection to the Praesideo network. It connects, one-to-one, to the call station interface, PRS-CSI, which is part of the Praesideo optical network. 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. The PRS-CSR can be extended with up to 16 keypads (LBB 4432/00 or LBB 4434/00), each with eight programmable keys. Extension with a numeric keypad (PRS-CSNKP) is also possible.