Alarm indication signal: Difference between revisions

Revision as of 00:38, 10 March 2012

Revision as of 00:46, 13 March 2012

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{{Unreferenced stub|date=December 2009}}

{{Redirect|AIS-P|the data packet protocol|Automatic Independent Surveillance-Privacy}}

{{Unreferenced stub|date=December 2009}}

'''Alarm indication signal''' ('''AIS''') (also called “all ones” because of the data and framing pattern) is a signal transmitted by an intermediate element of a multi-node transport circuit that is part of a concatenated [[telecommunications system]] to alert the receiving end of the circuit that a segment 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. The AIS replaces the failed data, allowing the higher order system in the concatenation to maintain its transmission framing integrity. Downstream intermediate elements of the transport circuit propagate the AIS onwards to the destination element.

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These are [[SONET]] OC-xx level indications that indicate if the errored element is in a section, segment, line segment, or path segment of the SONET circuit.

{{FurtherFurther2|Digital Signal 1#Connectivity and alarms}}

Middle 20th century analog [[carrier system]]s had Carrier Group Alarms by which the failure of a [[pilot signal]] was alerted to [[telephone exchange]] equipment, imposing an automated make-busy condition so the trunks carried by the failed system would not be used. The improved AIS originated with the [[Digital_Signal_1#Alarms|T-carrier]] system, and became a standard feature of subsequent [[plesiochronous]] and [[Synchronous circuit|synchronous]] circuit-based communication systems, and is also part of the [[asynchronous transfer mode|ATM]] standards.