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ISDN interface unit

  • US 5,764,643 A
  • Filed: 01/31/1997
  • Issued: 06/09/1998
  • Est. Priority Date: 11/29/1990
  • Status: Expired due to Fees
First Claim
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1. An ISDN interface unit coupled between a data processing unit and an ISDN line, comprising:

  • a digital signal communication circuit; and

    a voice band signal communication circuit;

    one of said digital signal and voice band signal communication circuits being selected by said ISDN interface unit based on a control channel signal on the ISDN line, so that transmission is initially carried out on the ISDN line in a form to match the digital signal communication circuit, andwhen a response from a communication partner is received, communication is carried out by using the digital signal communication circuit; and

    when a disconnect message is received instead of the response, a retransmission is automatically carried out to match the voice band signal communication circuit.

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