Alarm indication signal
Encyclopedia
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.
There are various AIS formats based on the signaling level of the errored circuit. When an element of T-1 or (DS-1
) circuit loses signal (LOS
) or framing (OOF), 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 valid DS-3 frame with the overhead bits (the M-subframe alignments 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 DS-3 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:
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.
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 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 OA&M
function has led to the development of a similar Ethernet alarm indication signal (EthAIS).
There are various AIS formats based on the signaling level of the errored circuit. When an element of T-1 or (DS-1
Digital Signal 1
Digital signal 1 is a T-carrier signaling scheme devised by Bell Labs. DS1 is a widely used standard in telecommunications in North America and Japan to transmit voice and data between devices. E1 is used in place of T1 outside North America, Japan, and South Korea...
) circuit loses signal (LOS
Loss of Signal
-History:Loss of Signal is the first full length studio album released by the Australian band Borne.-Track listing:#"Don't Go Now"#"Upside Down"#"The Guide"#"Beautiful"#"Morning Star"#"Easily"#"Coma"#"One Last Time"#"Chariots"...
) or framing (OOF), 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 valid DS-3 frame with the overhead bits (the M-subframe alignments 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 DS-3 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)
These are SONET
Sonet
Sonet may refer to:* Sonet Records, European record label* Synchronous optical networking * Saab Sonett...
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
Carrier system
In telecommunication, a carrier system is a multichannel telecommunications system in which a number of individual channels are multiplexed for transmission...
s had Carrier Group Alarms by which the failure of a pilot signal
Pilot signal
In telecommunications, a pilot is a signal, usually a single frequency, transmitted over a communications system for supervisory, control, equalization, continuity, synchronization, or reference purposes....
was alerted to telephone exchange
Telephone exchange
In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...
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 system, and became a standard feature of subsequent plesiochronous
Plesiochronous
The term Plesiochronous is derived from the Greek plesio, meaning near, and chronos, time, and refers to the fact that plesiochronous systems run in a state where different parts of the system are almost, but not quite perfectly, synchronised....
and synchronous
Synchronous circuit
A synchronous circuit is a digital circuit in which the parts are synchronized by a clock signal.In an ideal synchronous circuit, every change in the logical levels of its storage components is simultaneous. These transitions follow the level change of a special signal called the clock...
circuit-based communication systems, and is also part of the ATM
Asynchronous Transfer Mode
Asynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...
standards.
As the use of Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
for long-distance data links has increased, the need for a similar end-to-end OA&M
OA&M
Operations, administration and management or operations, administration and maintenance is a general term used to describe the processes, activities, tools, standards, etc involved with operating, administering, managing and maintaining any system...
function has led to the development of a similar Ethernet alarm indication signal (EthAIS).