Alarm indication signal
Alarm indication signal (AIS) is a signal transmitted by a system that is part of a concatenated telecommunications system to let the receiver know that some remote part of the end-to-end link has failed at a logical or physical level, even if the system it is directly connected to is still working. Other systems attached to a system transmitting AIS then relay the AIS indication onwards to other systems.
There are a number of types of AIS signals, which signal failure of different logical or physical segments of the system, including:
- Alarm indication signal path (AIS-P)
- Alarm indication signal line (AIS-L)
AIS originated with the T-carrier system, and became a standard feature of subsequent plesiochronous and synchronous circuit-based communication systems, and is also part of the ATM standards. As the use of Ethernet for long-distance data links has increased, the need for a similar end-to-end OAM function has led to the development of a similar Ethernet alarm indication signal (EthAIS).
Automatic Independent Surveillance - Privacy (AIS-P) is a data packet protocol for the TailLight system of Traffic Collision Avoidance wherein a signal is transmitted by an aircraft ATCRBS or Mode S transponder and received by aircraft and Air Traffic Control on the ground. This is an augmentation to transponders which states aircraft position and velocity in such a way as to minimize interference with any other avionics system, maximize the possible number of participating aircraft, while not relying on any equipment on the ground, and protecting aircraft from potential attack.