Ringing tone

Ringing tone (audible ringing, also ringback tone) is a signaling tone in telecommunication that is heard by the originator of a telephone call while the destination terminal is alerting the receiving party. Audible ringing is typically a repeated tone that is not necessarily synchronous with the cadence of the power ringing signal that is sent to the called party.
Audible ringing is usually generated in the switching system closest to the calling party, especially when under the control of strict implementations of Signalling System No. 7 and the Customized Application of Mobile Enhanced Logic (CAMEL) signaling system. It may also be generated in the distant switch, transmitted in-band, so that in analog networks the caller could monitor the quality of the voice path of the connection before the call is established. Remote call progress indication permits customized tones or voice announcements by a distant switch in place of the ringing tone.
The ringing tone is often also called "ringback tone". However, in formal telecommunication specifications that originate in the Bell System in North America, ringback has a different definition. It is a signal used to recall either an operator or a customer at the originating end of an established telephone call. It is also needed for coin-telephone lines to ring the telephone when the customer has hung up prematurely, for example to collect required overtime charges.
National characteristics.
Europe.
Many European countries use tones which follow the recommendation of the European Telecommunications Standards Institute. Almost all of these tones are 425 Hz; France uses 440 Hz. Typically, the pattern is 1 second of tone followed by 3 to 5 seconds of silence.
Japan.
In Japan, the standard audible ringing tone is a repeating 1-second tone with a 2-second pause between. The tone has a frequency of 400 ± 20 Hz, and the amplitude modulation is 15 to 20Hz.
North America.
In North America (excluding Mexico, Central America and parts of the Caribbean), the standard audible ringing tone is a repeated cadence of a two-second tone and four seconds of silence. The signal is composed of the frequencies and .
United Kingdom, Ireland, Commonwealth nations.
In the United Kingdom, Republic of Ireland, Australia, New Zealand, and many Commonwealth nations, it is a double ring. For most countries, it consists of a 0.4-second pulse, a 0.2-second pause, a 0.4-second pulse, and a 2-second pause. In all cases except Australia, the pulse is made by mixing a 400 Hz and 450 Hz sine wave; Australia uses up to three different combinations of frequencies. The example shown is created by mixing 400, 425, and 450 Hz sine waves.
India.
In India, the ringing tone is called "caller ringback tone" (CRBT), which varies with different network operators.
Personalized ringing tones.
Some telecommunication carriers have offered a service called of "ringback tones", which play a song of the subscriber's choice in lieu of the standard ringing tone. 
Patents for personalized ringing tone delivery systems were first filed in Korea by Kang-seok Kim (10-1999-0005344) in October 1999 and in the United States by Mark Gregorek "et al." (U.S. patent 5,321,740), and Neil Sleevi (U.S. patent 4,811,382). The first functional ringing tone replacement system was invented by Karl Seelig (U.S. patents 7,006,608 and 7,227,929). In 2001, Seelig's prototype was described in the Orange County Register and the Economist Magazine. Onmobile Global Ltd. India filed a patent entitled "Method and system for customizing ringing tone in an inter-operator telecommunication system" on Nov, 18 2010.
The first US national carrier offering this service was Verizon Wireless in 2004. Because of low sales, AT&T stopped offering ringback tones in 2014.
Ringback music.
Also known as caller tunes in some countries, such as India, ringback music is a service offered by mobile network operators to permit subscribers to select music or even install personalized recorded sounds for audible ringing.
Ringback advertising.
Ringback tone advertising (AdRBT) was introduced using a range of models in several commercial markets in 2008. In America, Ring Plus offered the first interactive advertisement platform. In Turkey, 4play Digital Workshop launched 'TonlaKazaan' AdRBT with Turkcell, and Xipto AdRBT launched in the United States with Cincinnati Bell wireless; OnMobile launched an Ad-supported Music RBT program in India with Vodafone. 4Play Digital workshop accumulated several hundred thousand users of their service in the first few months of commercial deployment, and received an innovation award in February 2009 at the Mobile World Congress in Barcelona. AdRBT typically rewards the caller or the called party with discounted Music RBT service, free minutes, cash, or other rewards in return for accepting advertising messages integrated with Music Ringback, or for selecting advertisements instead of music as a personalized advertising ringback.
In May 2011, Adfortel started the first ad-sponsored calling service in Austria with Orange, with users hearing a targeted advertisement instead of the regular waiting ring tone.
A Juniper Research report released in January 2011 predicts that ringback tone advertising will reach $780 million annually by 2015.
Interactive reverse ringing tone.
Interactive reverse ringback tones (IRRBT) are the same as normal ringback tones but have interactive functionalities and are targeted to the person who configures the tone. IRRBTs are heard on the telephone line by the caller who sets the IRRBT while the phone they are calling is ringing. 
Unlike the RBT, the IRRBT is often generated in the nearest switch and transmitted in-band, so the IRRBT will take precedence if both are configured.
Social network ringback tones provide interactive social network content to subscribers. Mixcess is the first platform (social network) using IRRBTs in the United States. The IRRBT was developed by Ring Plus, Inc. (U.S. Patent No. 7,227,929 invented by Karl Seelig, et al.). The IRRBT can be used to share videos, music and messages from friends.