Alarm indication signal

The alarm indication signal (AIS, english alarm indication signal) is a signal that indicates that no signal is received at a port in telecommunications. It signals the occurrence of a fatal error ( loss of signal ). The time within which such a fault must be detected by the standards of the relevant standardization organizations in the millisecond range. In the North American division multiplexing a yellow indicator light is turned on in the presence of this error, which is why this alarm is there also denoted by yellow alarm is detected. If a multiplexer receives no signal on any transmission path to a tributary port, he can not enter multiplexed into an aggregate signal. He replaced it, therefore, as a rule by a permanent one. The next multiplexer in the signal path, receives this permanent one, this indicates that an error has been registered already on the device in front of him. He leads this all ones on, so that all devices in the transmission path they receive. There are variations of this method: will be inserted by some devices rather than a permanent one, a 0101 episode.

Is on the devices of the multiplexing technique, a frame-structured information signal transmitted as it is present in the SDH or PDH, the all ones is usually only added to the payload of the signal, the OAM overhead but further transmitted unaffected. In case of loss of synchronization of the total signal (loss of synchronization ) or the frame signal (loss of frame ) but that is no longer possible. In SONET, this is a distinction with the codes AIS -L (line AIS) and AIS -P (path AIS).

In bi-directional data transfer, there is often a feAIS: a far end alarm indication signal. So that a device that has no signal to a port, the sending unit in the opposite direction of the error signals. Also the overhead used. The cell- oriented data transmission uses specially encoded ATM AIS cells, indicating a loss of signal or loss of cell synchronization ( Header Error Check).

• Multiplexing technique
• Signal