telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is i ...

, a message-waiting indicator (MWI) is a

Telcordia Technologies iconectiv is a supplier of network planning and network management services to telecommunications providers. Known as Bellcore after its establishment in the United States in 1983 as part of the break-up of the Bell System, the company's name ...

(formerly

Bellcore iconectiv is a supplier of network planning and network management services to telecommunications providers. Known as Bellcore after its establishment in the United States in 1983 as part of the break-up of the Bell System, the company's name ...

) term for an FSK-based

telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...

calling feature that illuminates an LED on selected

telephones A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into ele ...

to notify a telephone user of waiting

voicemail A voicemail system (also known as voice message or voice bank) is a computer-based system that allows users and subscribers to exchange personal voice messages; to select and deliver voice information; and to process transactions relating to ind ...

messages on most North American public telephone networks and PBXs. As described in Telcordia Generic Requirements documen
GR-283-CORE
a Message_Waiting_Indicator (MWI) is a mechanism that informs the subscriber about the status of recorded messages. The subscriber may subscribe to a notification feature that makes use of the status of this MWI.

Difference to audible message waiting indicators

This feature is also frequently called (and abbreviated) as visual message waiting indicator (VMWI). A VMWI, as defined i
Telcordia GR-1401-CORE
is a stored program controlled switching (SPCS) system feature that activates and deactivates a visual indicator on

customer-premises equipment In telecommunications, a customer-premises equipment or customer-provided equipment (CPE) is any terminal and associated equipment located at a subscriber's premises and connected with a carrier's telecommunication circuit at the demarcation po ...

(CPE) to notify the customer that new messages are waiting. VMWI differs from existing features that use other message indicators, such as audible stuttered

dial tone A dial tone is a telephony Signaling (telecommunication), signal sent by a telephone exchange or private branch exchange (PBX) to a terminating device, such as a telephone, when an off-hook condition is detected. It indicates that the exchange is ...

, in that it activates a visual indicator on the CPE. The visual indicator may be as simple as lighting or flashing a

light-emitting diode A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (co ...

(LED), or as advanced as displaying a special message on a liquid-crystal display (LCD). This technology was invented by Jerome (Jerry) Schull and Wayne Howe at BellSouth's Advanced Technology R&D group in 1992 and was issued as US Patent
#5,363,431
and

It was introduced in 1995, with the introduction of CLASS-based calling features and ADSI. It was at one time only compatible with ADSI-compliant telephones but is now compatible with any customer premises equipment ( CPE) that simply responds visually to visual FSK.

Use of similar indicator on standalone Caller ID set-top boxes

This service is often erroneously associated with the abilities of most

Caller ID Caller identification (Caller ID) is a telephone service, available in analog and digital telephone systems, including voice over IP (VoIP), that transmits a caller's telephone number to the called party's telephone equipment when the call i ...

standalone set-top boxes. Caller ID boxes manufactured after 1998 feature an LED that blinks green to notify that new calls have been recorded and red to indicate that a subscriber has new voicemail messages waiting. Some units also display the text "MESSAGE WAITING" (similar to ADSI-compliant telephones). These units do not use visual FSK to activate their red LEDs, but instead, they briefly " pick-up" the line at certain intervals (normally, within two minutes of a new call) to check for a "stuttered"

. The presence of a stutter dial tone activates a red LED; while absence deactivates it.

Mobile telephony

For

mobile phone A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link whi ...

s, the message-waiting indicator is sent via a Short Message Service (SMS) message — the same system used for texting. (SMS was actually invented for utilitarian uses like this, not for user conversation.) It not only indicates that a message is waiting, but also how many unheard messages there are on the voicemail

server Server may refer to: Computing *Server (computing), a computer program or a device that provides functionality for other programs or devices, called clients Role * Waiting staff, those who work at a restaurant or a bar attending customers and su ...

for that

telephone number A telephone number is a sequence of digits assigned to a landline telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices f ...

. In the event that a phone is deactivated, out of range, or otherwise removed from the network, there is often no way to clear this indicator until another message is recorded to the system, causing the MWI message to be sent again once the phone reconnects. The

customer service Customer service is the assistance and advice provided by a company to those people who buy or use its products or services. Each industry requires different levels of customer service, but in the end, the idea of a well-performed service is that ...

call center for the mobile network operator may also be able to provide simple

technical support Technical support (abbreviated as tech support) is a call centre type customer service provided by companies to advise and assist registered users with issues concerning their technical products. Traditionally done on the phone, technical suppor ...

to reset this by resending the MWI message manually.

Difference to audible message waiting indicators

Use of similar indicator on standalone Caller ID set-top boxes

Mobile telephony

See also