6 Optical Signalling at NT1+2a/b
The equipment has 2 LED to display various operating states. The states marked in
bold letters denote the display state in normal mode.
LED ~ (yellow) ON local main power supply (230 V ~)
OFF remote power (no local power supply)
LED U (green) ON U interface is activated, an ISDN device is
connected at S/T interface, Layer 1 is activated
Flash slow (1 Hz) U interface is activated, no ISDN device is
connected at S/T interface; Layer 1 is activated
via the analogue ports
Flash fast (8 Hz) U interface in synchronisation state,
permanently in error case at U interface
OFF Layer 1 is deactivated (in “sleep” mode)
7 Connection configuration