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

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Hokari, Makoto
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): BLUM, RUSSELL
• Application Number:
  US07/784,507
• Time in Patent Office: 566 Days
• Field of Search: 370/110.1, 370/54, 379/220, 379/221, 379/229-234
• US Class Current: 370/384
• CPC Class Codes: H04Q 11/0428 Integrated services digital network, i.e. systems for transmission of different types of digitised signals, e.g. speech, data, telecentral, television signals
• CPC Class Codes: H04Q 2213/1304 Coordinate switches, crossbar, 4/2 with relays, coupling field
• CPC Class Codes: H04Q 2213/13103 Memory
• CPC Class Codes: H04Q 2213/13106 Microprocessor, CPU
• CPC Class Codes: H04Q 2213/13205 Primary rate access, PRI
• CPC Class Codes: H04Q 2213/13209 ISDN
• CPC Class Codes: H04Q 2213/1322 PBX
• CPC Class Codes: H04Q 2213/13384 Inter-PBX traffic, PBX networks, e.g. corporate networks
• CPC Class Codes: H04Q 2213/13395 Permanent channel, leased line
• CPC Class Codes: H04Q 2213/13396 Signaling in general, in-band signalling
• CPC Class Codes: H04Q 2213/13399 Virtual channel/circuits

Abstract

In a private network where PBXs (1, 2) are connected through a primary rate interface (47, 48) to an ISDN network (45), one of the PBXs has routing data for virtual tie trunks for signaling and speech transmission, respectively, to be established via the ISDN to a distant PBX (2), and channel status data indicating their set-up or clear-down state according to time of day and calendar day. The stored data is periodically accessed, and depending on the contents of the channel status data, a call setup or clearing message is sent from the PBX (1) to the ISDN to set-up or clear-down the virtual tie trunks. On receipt of a response from the distant PBX, busy/idle status of the virtual tie trunks is changed according to the accessed channel status data. In response to a request from a user station, a path is established therefrom to the virtual speech tie trunk and a call setup message is sent direct to the distant PBX through the virtual signaling tie trunk.

Claims

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.

2. A private switched communications system as claimed in claim 1, wherein said first channel status data is stored in a bit map comprising a matrix array of cells each containing binary 1 or 0 indicating respectively the set-up or clear-down state of the virtual tie trunk, and wherein each column of the matrix array signifies a time span which is a fraction of one hour and each row of the matrix array signifies a portion of a twenty-four hour time span.

3. A private switched communications system as claimed in claim 1, wherein said PBX system includes means for checking the working/nonworking status of said virtual tie trunk to produce a status report, and wherein said control means includes means for transmitting a status enquiry message to said ISDN network to check the working/nonworking status of said virtual tie trunk with said ISDN network and receive a status report from the ISDN network, determining if the received status report matches or mismatches the status report of the PBX system, transmitting a call clearing message to said ISDN network when said status report is determined to be mismatched with the status report of the PBX system, and 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 to nonworking state following reception of the last-mentioned response message.

4. A private switched communications system having first and second PBX (private branch exchange) systems connected through a respective primary rate interface to an ISDN (Integrated Services Digital Network) public network, said first PBX system comprising:

memory means for storing routing data identifying a virtual signaling tie trunk and a virtual speech tie trunk to be established by speech channels of the primary rate interface, first channel status data indicating set-up/clear-down command status of the virtual signaling and speech tie trunks, and second channel status data indicating working/nonworking status of said virtual tie trunks, 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 signaling and speech tie trunks between the first and second PBX systems according to contents of said channel status data, receiving a response message from the distant PBX system, causing the working/nonworking status of said virtual signaling and speech tie trunks in said memory means to change according to said first channel status data following reception of said response message, causing a path to be established in the first PBX system from one of the user stations to one end of said virtual speech tie trunk in response to a call request therefrom when the status of said virtual speech tie trunk is indicative of the working state, and transmitting a call setup message to said second PBX system through said virtual signaling tie trunk to establish a path from the other end of the virtual speech tie trunk to a destination user station.

5. A private switched communications system as claimed in claim 4, wherein said first channel status data is stored in a bit map comprising a matrix array of cells each containing binary 1 or 0 indicating respectively the set-up or clear-down state of the virtual signaling and speech tie trunks, and wherein each column of the matrix array signifies a time span which is a fraction of one hour and each row of the matix array signifies a portion of a twenty-four hour time span.

6. A private switched communications system as claimed in claim 4, wherein said first PBX system includes means for checking the working/nonworking status of said virtual speech tie trunk to produce a status report, and wherein said control means includes means for transmitting a status enquiry message to said ISDN network to check the working/nonworking status of said virtual speech tie trunk with said ISDN network and receive a status report from the ISDN network, determining if the received status report matches or mismatches the status report of the first PBX system, transmitting a call clearing message to said ISDN network when said status report is determined to be mismatched with the status report of the first PBX system, and receiving a response message from said second PBX system, causing the working/nonworking status of said virtual speech tie trunk in said memory means of the first PBX system to change to nonworking state following reception of the last-mentioned response message.

7. A method for establishing a virtual tie trunk between first and second PBX (private branch exchange) systems each being connected through a respective primary rate interface to an ISDN (Integrated Services Digital Network) public network, the method comprising the steps of:

a) storing routing data identifying a virtual tie trunk to be established by one of the speech channels of said primary rate interfaces;

b) periodically generating channel status data indicating set-up or clear-down state of the virtual tie trunk, said channel status data being variable as a function of time and as a function of calendar day;

c) transmitting a call setup message or a call clearing message through a signaling channel of the primary rate interface of the first PBX system to said ISDN public network to set-up or clear-down said virtual tie trunk according to contents of the first channel status data;

d) receiving a response message from said second PBX system;

e) indicating working/nonworking status of said virtual tie trunk in said memory means according to said channel status data upon receipt of the response message; and

f) establishing a path from one of said user stations to said virtual tie trunk in response to a request therefrom when said status of said virtual tie trunk is indicative of the working state.

8. A method for establishing virtual tie trunks between first and second PBX (private branch exchange) systems each being connected through a respective primary rate interface to an ISDN (Integrated Services Digital Network) public network, the method comprising the steps of:

a) storing routing data identifying a virtual signaling tie trunk and a virtual speech tie trunk to be established by ones of the speech channels of said primary rate interfaces;

b) periodically generating channel status data indicating set-up or clear-down state of the virtual signaling and speech tie trunks, said channel status data being variable as a function of time and as a function of calendar day;

c) transmitting a call setup message or a call clearing message to said ISDN public network to set-up or clear-down said virtual signaling and speech tie trunks through a signaling channel of the interface of the first PBX system according to contents of the channel status data;

d) receiving a response message from said second PBX system;

e) indicating working/nonworking status of said virtual tie trunk in said memory means according to said channel status data upon receipt of the response message;

f) establishing a path from one of said user stations of the first PBX system to one end of said virtual speech tie trunk in response to a request therefrom when said working/nonworking status of said virtual speech tie trunk is indicative of the working state; and

g) transmitting a call setup message to said second PBX system through said virtual signaling tie trunk to cause a path to be established from the other end of the virtual speech tie trunk to a destination user station of the second PBX system.