Camp-on busy signal

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In telecommunication, the term camp-on busy signal has the following meanings:

• A signal that informs a busy telephone user that another call originator is waiting for a connection. Synonym: call waiting
• A teleprinter exchange facility signal that automatically causes a calling station to retry the call-receiver number after a given interval when the call-receiver teleprinter is occupied or the circuits are busy. Synonym: speed-up tone

 This article incorporates public domain material from the General Services Administration document: "Federal Standard 1037C".