A lighted Remote Down led means there is no communication with the remote MultiMux. The composite link CTS, XMT, RCV, and CD leds will normally be on when a connection is established. If the CD indicator is off, the local composite link device (modem, DSU, ISDN TA) does not have a a connection to the remote composite link device. Verify the configuration of the composite link devices and try connecting the MultiMuxes back-to-back. If they connect back-to-back, the problem is due to a bad line. Contact your service provider.