The PRS-CSRM is a module with the same functionality as the remote call station, PRS-CSR, but without its housing and other components. It is a building block to make custom call stations or panels. It connects via a CAT-5 cable, 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 CAT-5 cable does not contribute to the Praesideo optical network length. This considerably increases the overall possible length of the network. The PRS-CSRM can be extended with up to 16 keypads (LBB 4432/00 or PRS-CSKPM), each with eight configurable keys. Extension with a numeric keypad (PRS-CSNKP) is also possible.