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.