| 摘要 |
Disclosed is a method for communication with no power feed in an exchange. (1) A calling subscriber unit transmits a special service code designating the disuse of a direct current loop together with the numeric information on the called subscriber unit to the exchange after formation of a direct current loop. (2) When the special service code is received, an on-hook transmission state in which the transmission and reception of an alternating current signal is possible between the subscriber line interface circuit and the calling subscriber unit even if no direct current loop is formed is established in the subscriber line interface circuit to which the calling subscriber unit which has transmitted the special service code is connected. (3) The calling subscriber unit disconnects the direct current loop, and the exchange maintains the speech path between the calling subscriber unit and the called subscriber unit even after the direct current loop is disconnected. (4) An alternating current signal is transmitted and received between the subscriber line interface circuit and the calling subscriber unit in the state in which no direct current loop is formed.
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