- Alarm indication signal
Alarm indication signal (AIS) is a signal transmitted by a system that is part of a concatenated
telecommunications systemto 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)
Middle 20th century analog
carrier systems had Carrier Group Alarms by which the failure of a pilot signalwas alerted to telephone exchangeequipment, imposing an automated make-busy condition so the trunks carried by the failed system would not be used. The improved AIS originated with the T-carriersystem, and became a standard feature of subsequent plesiochronousand synchronouscircuit-based communication systems, and is also part of the ATM standards.As the use of Ethernetfor long-distance data links has increased, the need for a similar end-to-end OA&Mfunction has led to the development of a similar Ethernet alarm indication signal ( EthAIS).
* concatenation (telecommunications)
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