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Ringing tone

Audible electrical signal in telecommunication systems

  • 7 min read
  • 3 chapters

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Purpose and description

When a telephone user initiates a telephone call, typically by dialing or selecting a telephone number on a telephone, the progress or status of the call attempt is indicated to the user audibly by several types of call progress tones. For example, during the period of routing the call across the public switched telephone network (PSTN) the call may encounter congestion on a particular link. If this cannot be automatically resolved, the calling user receives the congestion tone, also called reorder tone. If the called station is already busy and cannot accept a second call via call waiting, the calling party is alerted with a busy signal. When the call routing is successful and the receiving telephone is not already in a call, the destination telephone receives an electrical signal, called power ringing, or the ring tone, to alert the recipient of the incoming call. During this period of alerting, the caller also receives a distinctive signal, audible ringing, also called ringing tone.

Audible ringing is typically a repeated burst of tone that is typically not synchronous with the cadence of the power ringing signal at the destination. It 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.

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.

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