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Private network with means for establishing virtual tie trunks between PBXS through ISDN public network

  • US 5,212,691 A
  • Filed: 10/30/1991
  • Issued: 05/18/1993
  • Est. Priority Date: 10/30/1990
  • Status: Expired due to Fees
First Claim
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1. A private switched communications system having a PBX (private branch exchange) system connected through a primary rate interface to an ISDN (Integrated Services Digital Network) public network, wherein the PBX system comprising:

  • memory means for storing routing data identifying a virtual tie trunk to be established by one of speech channels of the primary rate interface, first channel status data indicating set-up/clear-down command status of the virtual tie trunk, and second channel status data indicating working/nonworking status of said virtual tie trunk, said first channel status data being variable as a function of time and as a function of calendar day; and

    control means for accessing said first channel status data at periodic intervals, transmitting a call setup message or a call clearing message to said ISDN public network through a signaling channel of the primary rate interface to set-up or clear-down said virtual tie trunk between said PBX system and a distant PBX system according to contents of said first channel status data, receiving a response message from said distant PBX system, causing the working/nonworking status of said virtual tie trunk in said memory means to change according to said first channel status data following receipt of said response message, and causing a path to be established in said PBX systems to establish a connection from a user station of said PBX system to a user station of said distant PBX system via said virtual tie trunk in response to a call request when said working/nonworking status of said virtual tie trunk is indicative of the working state.

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