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9-1-1 Switched access system

  • US 5,239,570 A
  • Filed: 07/25/1990
  • Issued: 08/24/1993
  • Est. Priority Date: 07/25/1990
  • Status: Expired due to Fees
First Claim
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1. A 9-1-1 switched access system for creating a reliable emergency telephone communication channel between a central office that receives emergency calls and the telephone communication equipment of a public service answering point (PSAP) using the shared trunks of a public service telephone network (PTN), said 9-1-1 switched access system comprising:

  • (a) a public service telephone network (PTN) including at least a 9-1-1 central office and a PSAP central office, said 9-1-1 central office including line ports connected to a plurality of telephone subscribers and a trunk port to which emergency calls received from subscribers connected to the line ports are sent, said PSAP central office including a PSAP line port, said 9-1-1 central office and said PSAP central office connected together by shared trunks;

    (b) a trunk dial unit (TDU) having an input connected to the trunk port of said 9-1-1 central office to which emergency calls are sent and an output connected to a line port of said 9-1-1 central office for;

    (i) dialing the number of said PSAP line port and coupling the input of said TDU to the output of said TDU, in response to a call from said 9-1-1 central office; and

    (ii) automatically dialing the number of said PSAP line port, sending a test call message, and generating an alarm if a response to said test call message is not received, in between responding to calls from said 9-1-1 central office; and

    (c) a call access unit (CAU) having an input connected to the PSAP line port of said PSAP central office and an output suitable for connection to the telephone communication equipment of a PSAP for;

    (i) applying an alert PSAP message to the output of said CAU and coupling the input of said CAU to the output of said CAU, in response to the receipt of a ring signal from said PSAP central office followed by the absence of a test call; and

    (ii) applying a response to the input of said CAU in response to the receipt of a ring signal from said PSAP central office followed by a test call.

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