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
A communications system or communication system is a collection of individual telecommunications networks, transmission systems, relay stations, tributary stations, and terminal equipment usually capable of interconnection and interoperatio ...
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.
There are various AIS formats based on the signaling level of the errored circuit. When an element of T1 or (
DS1) circuit loses signal (
LOS
LOS, or Los, or LoS may refer to:
Science and technology
* Length of stay, the duration of a single episode of hospitalisation
* Level of service, a measure used by traffic engineers
* Level of significance, a measure of statistical significance ...
) or framing (
OOF
Oof or OOF may refer to:
Acronyms
* Out of focus; see List of abbreviations in photography
* Other Official Flows, a categorization of foreign aid used by official development assistance
* Out of facility; see List of business and finance abbr ...
), the device replaces the erroneous data bits with a series of ones. This is where the term All Ones originates. At the
DS3 signal level, the intermediate element receiving an errored signal replaces the errored channel data with a signal consisting of a valid DS3 frame with the overhead bits (the M-subframe alignment bits, M-frame alignment bits, and P bits) with the payload set to a 1010... sequence, the C bits all set to zero, and the X bits set to one. This way, the integrity of the DS3 frame is maintained even though the underlying data was compromised.
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)12
These are
SONET
Synchronous optical networking (SONET) and synchronous digital hierarchy (SDH) are standardized protocols that transfer multiple digital bit streams synchronously over optical fiber using lasers or highly coherent light from light-emitting diode ...
OC-xx level indications that indicate if the errored element is in a section, segment, line segment, or path segment of the SONET circuit.
Middle 20th century analog
carrier system
A carrier system is a telecommunications system that transmits information, such as the voice signals of a telephone call and the video signals of television, by modulation of one or multiple carrier signals above the principal voice frequency or ...
s had Carrier Group Alarms by which the failure of a
pilot signal
In telecommunications, a pilot signal is a signal, usually a single frequency, transmitted over a communications system for supervisory, control, equalization, continuity, synchronization, or reference purposes.
Uses in different communication ...
was alerted to
telephone exchange
A telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syst ...
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
T-carrier
The T-carrier is a member of the series of carrier systems developed by AT&T Bell Laboratories for digital transmission of multiplexed telephone calls.
The first version, the Transmission System 1 (T1), was introduced in 1962 in the Bell System ...
system, and became a standard feature of subsequent
plesiochronous
In telecommunications, a plesiochronous system is one where different parts of the system are almost, but not quite, perfectly synchronised. According to ITU-T standards, a pair of signals are plesiochronous if their significant instants occur at ...
and
synchronous
Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronou ...
circuit-based communication systems, and is also part of the
Asynchronous Transfer Mode
Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by American National Standards Institute (ANSI) and ITU-T (formerly CCITT) for digital transmission of multiple types of traffic. ATM was developed to meet the needs of ...
standards.
As the use of
Ethernet
Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...
for long-distance data links has increased, the need for a similar end-to-end
OA&M
Operations, administration and management or operations, administration and maintenance (OA&M or OAM) are the processes, activities, tools, and standards involved with operating, administering, managing and maintaining any system. This commonly ...
function has led to the development of a similar
Ethernet alarm indication signal (EthAIS).
Synchronous optical networking
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