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Reference.org
Supervision (telephony)
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<p>In <a href="/facts/Telecommunication/vxoj1cxR">telecommunication</a>, supervision is the monitoring of a telecommunication circuit for <a href="/facts/Telephony/2GwTTepw">telephony</a> to convey to an operator, user, or a switching system, information about the operational state of the circuit. The typical operational states of trunks and lines are the idle and busy states, seizure, and disconnect. The states are indicated by various electrical signals and electrical conditions depending on the type of circuit, the type of terminating equipment, and the type of intended service. </p><p>Answer and disconnect supervision are functions of <a href="/facts/Line_signaling/2QM6BqXM">line signaling</a> that convey circuit seizure and disconnect. Answer supervision indicates that a call has been answered. Disconnect supervision provides a signal that the call has been disconnected. </p><p>For example, the <a href="/facts/Called_party/TxXCTuQT">called party</a> may indicate to the <a href="/facts/Telephone_exchange/PaRpGm8I">telephone exchange</a> that the call is being disconnected by the <a href="/facts/Called_party/TxXCTuQT">called party</a> by allowing loop current to flow in the line, or the <a href="/facts/Called_party/TxXCTuQT">called party</a> indicates to the exchange that the call is being answered. </p>