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Private branch exchange system

  • US 5,581,612 A
  • Filed: 09/30/1993
  • Issued: 12/03/1996
  • Est. Priority Date: 02/22/1990
  • Status: Expired due to Fees
First Claim
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1. A private branch exchange system comprising:

  • an extension terminal; and

    an exchange unit which accommodates said extension terminal and an external line and connects said extension terminal and said external line via a main channel or a sub-channel, the extension terminal communicating with the external line before a power failure occurs via the main channel, and the extension terminal communicating with the external line during a power failure via the sub-channel,wherein said extension terminal includes;

    connecting means for connecting the exchange via the main channel or the sub-channel,detecting means for detecting use of said sub-channel, andholding means for holding a connection with the external line at restoration from the power failure in a case where use of said sub-channel is detected by said detecting means.

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