GB2097567A - Transmission of alarm information over telephone lines - Google Patents

Abstract

Apparatus for re-routing alarm information in a system in which the alarm information is transmitted from a subscriber's premises via a local processor and a central processor to one of a number of terminal stations. The apparatus includes a monitoring unit 59 for monitoring the condition of the transmission link between the central processor and each terminal station. If the unit 59 senses a fault on a transmission link it causes the alarm information which should have been transmitted over that link to its designated terminal to be redirected to another terminal station. <IMAGE>

Description

SPECIFICATION Improvements in or relating to the transmission of alarm information over telephone lines This invention relates to systems in which alarm information is transmitted via telephone lines from subscribers premises to one of a number of terminal stations.

An alarm system of this type has a plurality of transmitters which are located at subscribers premises each transmitter being adapted to transmit signals indicative of the state of its associated alarm to a telephone line, said signals being in the form of modulated carrier waves, a plurality of receivers located at one or more local exchanges for receiving the transmitted signals, the or each local exchange having a local processor which is arranged to sequentially scan the outputs of the receivers at its exchange and, when it detects a signal indicative of an alarm condition, to transmit a signal coded with information indicative of the subscriber identity and alarm information destination to a central processor which is operative to direct the alarm information to one of a number of terminal stations. Such an alarm system will be called a system of the kind referred to.

An alarm system of this type is described in U.K.

Patent Application No. 9246177. In the alarm system described in this Application the central processor has a plurality of local processor terminations one for each local processor, a plurality of terminal station terminations, highways linking the processor terminations and the terminal station terminations and means for sequentially scanning the local processor terminations, each terminal station termination being responsive to an alarm signal received by a processor termination and addressed with a particular code to direct that alarm signal to the appropriate termination. Each terminal station termination also includes a store for storing alarm information so that the alarm information can be redirected from one terminal station to another.

In a system of this kind the lines between the central processor and each terminal station are duplicated to allow for line failure. However, it can happen that both lines fail or that the transmission equipment used to transmit signals between the central processor and the terminal station fails, and in this situation the terminal station would not receive the required alarm message.

The present invention is concerned with an arrangement which will sense such a condition and arrange for the alarm message to be redirected to an alternative terminal station.

Thus according to the present invention there is provided apparatus for re-routing alarm information in a system of the kind referred to, said apparatus comprising means for monitoring the condition of the transmission link between the central processor and each terminal station, said monitoring means being responsive when it senses a fault on said transmission link to cause alarm information to be redirected from its designated terminal station to another terminal station. The monitoring means may include a bistable arrangement which is operative in response to a fault to inhibit said transmission link and provide an alternative transmission path for the alarm information. The apparatus may include means for substituting the existing terminal station address code with the code associated with the terminal station to which the information is to be re-directed.The apparatus can form part of the central processor.

The invention will be described now by way of example only with particular reference to the accompanying drawings. In the drawings: Figure 1 is a block schematic diagram of an alarm signalling system in which the present apparatus can be used; Figures 2a and 2b are a block schematic diagram illustrating a central processor used in the system of Figure 1, and Figure 3 is a block schematic diagram illustrating apparatus in accordance with the present invention.

The signalling system shown in Figure 1 of the drawings is for transmitting alarm signals from a subscriber's premises via existing telephone lines to one of a number of terminal stations or display locations where the alarm information is required e.g. police, fire, security and plant maintenance organisations. The alarm information is transmitted overthetelephone lines in encoded form and in such a manner that the signals do not interfere with normal speech signals on the telephone lines.

The system has transmitting equipment 10, 11 located in the subscriber's premises. Each piece of transmitting equipment 10, 11 is connected via a local public telephone line 12 to an associated receiver 14, 15. The receivers are located in a local exchange and are connected to a processor 16 in that exchange. The transmitter 10 produces a carrier signal on which is modulated alarm information. The modulated carrier is received by the associated receiver which produces an output in the form of single bit binary information which is fed to the local processor 16.

Each transmitter generates a carrier wave which is amplitude modulated, the modulation being switched in order to indicate the state of the alarm contact inputs. The associated receiver responds to the modulated carrier and produces an output in the form of single bit binary information which is fed to the local processor 16.

The system has a number of local exchanges (only one is shown in Figure 1 ) each of which contains a number of receivers all connected to a single local processor 16. Each processor 16 is arranged to continuously scan the outputs of the receivers connected to it. Each local processor 16 is connected by a dedicated line to a central processor 20 disposed at a central exchange. When a local processor detects an alarm condition from one of the pieces of alarm equipment it compiles a message containing subscriber identity and destination for the alarm and transmits this message to the central exchange 20. The central processor at the central exchange receives this message and directs it via a private line to an appropriate one of a number of display points 21. The display points can be located at a fire headquarters, police headquarters or a central display station.A connection can also be provided to a Post Office maintenance point. The system is described in more detail in U.K. Patent Application No. 9246;77.

Referring to Figures 2a and 2b the central processor of the system shown in Figure 1 comprises a plurality of local processor terminations 550 (only one shown in Figure 2a), a local processortermination being provided for each local processor. Each local processor termination comprises a TDMIFDM receiver 552 connected to receive signals from the local processor. The receiver 552 is connected to a test injection and gate circuit 553. The circuit 553 has data, address and control outputs 554, 555, 556 which are respectively connected to a data highway 558, an address highway 559 and a control highway 560. A remote test highway 562 is connected via a line 563 to a TDM/FDM transmitter 564 in the local processor termination 550. The test injection and gate circuit 553 is connected by a reset and release line 566 and a memory up date line 567 to the transmitter 564.A remote test generator 569 is connected to the remote test highway 562 and is operable by means of a key pad 570. The key pad 570 and remote test generator may be located at a Post Office maintenance terminal.

It will be appreciated that all other local processor terminations are connected to the highways 558, 559, 560 and 562 in a similar manner. This is indicated generally at 572. The control data and address highways 560. 558 and 559 are connected by control data and address lines 574,575 and 576 to a display termination 578. Only one displaytermination is shown in Figure 8 but a plurality of other display terminations may be connected to the highways 558, 559, 560 as indicated at 580. A maximum of 30 display terminations can be connected to the main highways. Each display termination has a test, check and store 582 which is connected to the lines 574, 575, 576. The test, check and store has data, call and reset outputs connected to a TDM!FDM transmitter 584 the output of which is connected by a line 585 to a display point.The test check and store 582 has a local test input 586 and a reset input 587 which is connected to an FDM;TDM receiver 588 which receives signals returned from the display point along line 585. The receiver 588 is also connected to the transmitter 584. The receiver 588 has call and address outputs which are connected to a test, injection and gate circuit 589 which has reset repeat data and address outputs connected respectively to the lines 574, 575 and 576. The gate 589 has a local test input 591 and an enable input 592. The gate 589 also has a data input from the data output of the store 582 and a control output which is connected to a reset input on the test, check and store 582.

The central processor also includes a test arrangement consisting of a highway test check circuit 595 connected by data and address lines 596 and 597 to the data and address highways. The output of the circuit 595 is connected to a scan generator 599 which in turn is connected to a test sequence generator 600. The scan generator 599 also receives outputs from highway test check circuits of other stages indicated at 601. Thus the scan generator 599 and test sequence generator 600 are common for all the display terminations.

The operation of the central processor is cyclic, the operation of the scan generator 599 being stopped only under fault conditions. All messages are therefore given equal priority. In use information received from a local processor is presented to the receiver 552 and gate 553 of the corresponding local proces sortermination from the output of the FDMiTDM link. The arrangement is such that the terminations 550 are enabled sequentially by means of signals derived from the scan generator 599. The scan generator 599 also generates local test control signals and a binary code to identify the local processor termination being examined. The enable signal generated by the generator 599 initially causes the gate 553 to generate test signals which are passed to the data and address highways 558 and 559.The test signal validity is checked by the local test check circuit 582 associated with the display termination 578 and a separate check circuit 595 connected directly to the highways. Then the gate input is examined to see if a call signal is present. If a call signal is present the data and address information is switched onto the highways for the remaining period of the enable signal.

Each display termination store 582 is programmed to recognise a specific address code. The display termination which recog nises the address code received from the local processor then tests to see if the store is empty or full. If the store is empty the data is loaded into the store and control signals are returned to the local processor termination which then signals memory up date and resetirelease to the local processor. A circuit within the local processortermination 550 ensures that once a call signal has been identified by the central prncessoritwill on subsequent scans be ignored until it has been removed and re-established by the local processor.

This is to ensure that the same message is not repeatedly loaded into the display termination 578.

Should the store 582 be full control information is returned to the local processor termination which then signals only release to the local processor and a flag is set in the store to indicate that a further message is waiting to be displayed. With the data loaded into the display termination store 582 the data together with a call signal is transmitted via the TDMiFDM link 584 to the display point. When the display point has recorded the message and acknowledgement signal is returned along line 585 to the receiver 588 in the display termination. A reset signal is then applied from the receiver 588 to the reset input 587 of the store to clear the store. The display is also subsequently cleared.

If it is required to transfer a message to a second display point the address of the selected new display and a call signal are returned to the display termination 578 in place of the acknowledgement signal. The data output from the store 582 is hard wired to the input of a gate which performs in a similar manner to a local processor termination gate. When this gate is supplied with call and address signals it is enabled in the same manner as a local processor termination gate and passes information onto the data and address highways 588, 559. If the second display termination is free the message is loaded into the new store and control signals return to reset the original display store and cancel the call and address signals for the original display point.If the second display termination is full a control signal is returned to the original display point to regenerate the call signal.

The present apparatus is designed to monitor the condition of the transmission link between the central processor and each terminal station. As shown in Figure 3 each buffer store 582 of the central processor is connected to transmission equipment 50 which is linked by a duplicated transmit path 51 to a a terminal station which includes a modem 52 and a printer 53. A duplicated return path 54 is provided from the modem to transmission equipment 55 at the central processor. The equipment 55 has an acknowledge output 56 which is connected to the buffer store 582. The equipment 55 also has two further outputs 61, 62 connected to the monitoring and re-route apparatus illustrated schematically at 59. The output 61 is arranged to carry a transfer address and transfer action enable signal and the output 62 is arranged to carry a transmission fault output signal.The monitoring and re-route apparatus includes a bistable circuit 60 having outputs to gates 63 and 64. The output from the gate 63 is connected to a unit 589 which is brought into operation in the event that alarm information is to be re-routed.

The unit 59 is designed to be incorporated as part of the central processor and operates as follows.

Under normal conditions when the transmission path between the central processor and the printer terminal is operating correctly the unit 59 is in such a condition that it allows an acknowledgement signal from the printer terminal to pass via lines 56 to the buffer store 582. The transfer signals also pass through the unit 59 to the central processor and are handled in the manner described in U.K. Patent Application No. 9246/77. If a fault occurs in the transmission path (e.g. there is a transmission equipment failure or a line failure the transmission equipment outputs a condition on the line 62 which is sensed by the bistable circuit 60 to trigger that bistable circuit.This causes the unit 59 to inhibit the return path information from the printer terminal to the central processor and also to break via R1 the forward transmission path between the central processor and the printer terminal. When the unit 59 has sensed a fault condition it substitutes in the unit 589 an address code for the new terminal to which alarm information is to be re-routed. The result of this is that any incoming alarm signal will cause the action enable to be diverted via line 67 and a contact 68 to the unit 589 so that the unit 589 accepts the alarm information for redirecting to the new terminal.

On restoration of the transmission link the bistable 60 of the unit 59 is automatically (or manually reset to its initial condition. This inhibits the unit 59 and restores the return path and forward transmission path between the central processor and printer terminal by way of R1.

Thus it will be seen that the unit 59 operates in the event of a fault in the transmission link between the central processor and printer terminals to inhibit that link and redirect alarm information from a subscribers alarm to a new terminal which can be any preselected terminal. The equipment can be provided with a programmable device for making the decision as to which terminal the alarm information should be re-routed to.

Claims (5)

1. Apparatus for re-routing alarm information in a system of the kind referred to, said apparatus comprising means for monitoring the condition of the transmission link between the central processor and each terminal station, said monitoring means being responsive when it senses a fault on said transmission link to cause alarm information to be redirected from its designated terminal station to another terminal station.

2. Apparatus as claimed in claim 1 wherein the monitoring means includes a bistable arrangement which is operative in response to a fault to inhibit said transmission link and provide an alternative transmission path for the alarm information.

3. Apparatus as claimed in claim 1 or claim 2 wherein the apparatus includes means for substituting the existing terminal station address code with the code associated with the terminal station to which the information is to be re-directed.

4. Apparatus as claimed in any preceding claim wherein the apparatus forms part of the central processor of the system.

5. Apparatus for re-routing alarm information substantially as hereinbefore described with reference to and as shown in the accompanying drawings.