30 FXS FXO to E1 PCM multiplexer POTS voice mux, DLC telephone extender voice over E1 mux, E&M, RS232, V.35, ... provide 30 channels of telephones with reversed polarity charging function and caller ID display function, with upstream E1.PRODUCT CHARACTER:1, Complete alarm signals ... operate although in power outage.4, Up-link is the voice equipment of E15, There are 30 channels of telephone interfaces ...