The layer 1 state of the primary rate interface active(F1) active, framing and synchronisation is o.k. This is the only state where data-transmission is possible remote-alarm(F2) receipt of an RAI, remote alarm indication, from the remote side; The remote-alarm is also known as yellow alarm or distant alarm no-signal(F3) no signal is received, RAI will be transmitted. NOS is also known as red alarm . no-sync(F4) signal is received but synchronistation is not possible, RAI will be transmitted The received signal may also consist of contingous Ones crc-error(F5) signal and synchronisation are o.k. but signal has heavy crc errors, RAI will be transmitted power-on(F6) initial state after power was switched on (transient) resync(7) Setting Layer 1 State to resync can be used to force resynchronisation The Layer1states are also visible in the isdnIfTable, but the state numbers are mapped to those of an BRI-Interface