Patent Publication Number: US-8121273-B2

Title: Call interceptor

Description:
FIELD OF THE INVENTION 
     The present invention relates to call interception and especially, but not exclusively, to the interception of facsimile transmissions. 
     BACKGROUND TO THE INVENTION 
     The receipt of unsolicited and unwanted facsimile transmissions (sometimes referred to as “spam” or “junk” transmissions) is an increasing problem. Spam transmissions are typically sent to a plurality of recipients by an automated machine that automatically dials a plurality of fax numbers, usually in sequence. Should the machine encounter a line that is busy, unanswered or otherwise unavailable, it abandons that particular call and moves on to the next fax number. The abandoned call is typically tried again at a later time. 
     SUMMARY OF THE INVENTION 
     Accordingly, a first aspect of the invention provides an apparatus for selectively allowing calls to a device that may receive calls on a signal line, the apparatus including means for detecting an incoming call on the signal line; and means for allowing the incoming call to reach the device if received during an enabled time period and preventing the incoming call from reaching the device if received outside the enabled time period. 
     In the preferred embodiment, the enabled time period is initiated in response to receiving a first incoming call after a quiescent period, outside of an enabled time period. 
     The apparatus may selectably block incoming calls by making or breaking the signal lines as appropriate, and/or by causing a signal to be sent on said signal line to the device sending the incoming call indicating that the receiving device is busy or otherwise unavailable (thereby effectively disabling the signal line). 
     The apparatus may adopt a normally enabled state in which the signal line is normally enabled (i.e. at least incoming calls are allowed to be received, the signal line being disabled (i.e. at least incoming calls are blocked by, for example, breaking the signal line or sending a busy/unavailable signal thereon) in response to detecting said first incoming call. 
     Alternatively, the apparatus may adopt a normally disabled state, the signal line being enabled only during said enabled time period. 
     The apparatus may include a switching device for selectably making or breaking the signal line. 
     A second aspect of the invention provides a method of selectively allowing calls to a device that may receive calls on a signal line, the method including detecting an incoming call on the signal line; allowing the incoming call to reach the device if received during an enabled time period; and preventing the incoming call from reaching the device if received outside the enabled time period. 
     In preferred embodiments, once a call has been received and allowed during the enabled time period, the signal line is enabled until the apparatus determines that the call has ended. This may be achieved by monitoring signal activity or voltages and/or currents on the signal line. 
     Preferred features are recited in the dependent claims and further advantageous aspects of the invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments and with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are now described by way of example and with reference to the accompanying drawings in which like numerals are used to indicate like parts and in which: 
         FIG. 1  is a block diagram showing an apparatus embodying the invention; 
         FIG. 2  is a schematic diagram showing a specific embodiment of the apparatus of  FIG. 1 ; and 
         FIG. 3  is a schematic diagram showing an alternative specific embodiment of the apparatus of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Referring now to the drawings, there is shown, generally indicated as  10 , an embodiment of an apparatus for intercepting calls. The apparatus  10  is connectable between a call receiving device in the form of, for example, a facsimile machine  12 , and a socket  14 . The socket  14  provides a connection point to a communications network (not shown), for example a public standard telephone network (PSTN) and/or a computer network. Hence, the facsimile machine  12 , or other device, may send and receive calls or transmissions to and from other devices (not shown) e.g. other facsimile machines, across the communications network. The term “calls” is intended to embrace any data transmission from one device to another and, in the present embodiment is particularly intended to embrace facsimile transmissions. In alternative embodiments, the call receiving device need not necessarily comprise a facsimile machine—it may comprise any device capable of receiving a call or data transmission on a line that can be blocked, especially a PSTN line or a mobile (cellular) telecommunications network line. For example, the call receiving device may comprise a telephone or computing device. Typically, the call receiving device is also capable of making outgoing calls. 
     In use, calls are sent between the socket  14  and the device  12  via a signal line  15 . Calls typically take the form of electrical signals and so signal line  15  is typically provided by one or more electrical signal carriers or cables. In the case where the socket  14  provides a connection to a PSTN, the line  15  is typically provided by an electrical cable comprising 4 wires or carriers  16 . During use, the line  15  provides part of a signal path between the device  12  and any one of said other devices connected to the network. In the examples described herein, the line  15  is assumed to be a conventional fax/phone line. 
     Conventionally, a fax line is provided by a cable connected directly between the socket  14  and the fax machine  12 . When the apparatus  10  is installed, the line  15  is selectably connectable to the fax machine  12  via the apparatus  10  as is described in more detail below. Typically, the line  15  is carried between the socket  14  and the apparatus  10  by a first cable, and between the apparatus  10  and the fax machine  12  by a second cable, the apparatus  10  itself also providing part of the line  15 . This can be seen from  FIGS. 2 and 3  where the apparatus  10  includes signal carriers  16  which provide, in use, part of the signal line. The line  15  is provided between first and second connectors  19 ,  21 , the first connector  19  be connected in use to socket  14  and the second connector  21  being connected in use to the device  12 . 
     The apparatus  10  includes a switching device  18  which, when the apparatus  10  is installed, is incorporated into the line  15 . In an open state, the switch device  18  breaks the line  15  thereby preventing calls from reaching, or being received by, the fax machine  12 . In a closed state, the switch device  18  makes the line  15  so that calls are transmitted to, or received by, the fax machine  12 . 
       FIG. 2  shows an embodiment of the switching device  18 . The switching device  18  comprises a plurality of switch contacts  22  each controlled by a single relay device  24 . For a conventional 4-wire fax line, a respective switch contact  22  is incorporated into 3 of the wires  16 . Each switch contact  22  can make or break a respective wire  16  depending on the state of the relay device  24 . Alternatively, each switch contact  22  may be operable by its own respective relay device (not illustrated). 
     A control unit  26  is provided for controlling the state of the switching device  18 . In the embodiment of  FIG. 2 , the control unit  26  controls the switching device  18  by causing the relay  24  to be energised or de-energised by applying appropriate voltages to the relay  24 , e.g. 5 volts to energise and 0 volts to de-energise. In the preferred embodiment, the switching device  18  adopts a normally closed state and so, in order to reduce power consumption, the relay  24  is advantageously arranged such that de-energisation corresponds to the closed state of switch contacts  22 , while energisation corresponds to the open state. 
     The control unit  26  conveniently comprises a suitably programmed micro-controller, but may comprise any other suitable data processor, controller or digital logic circuit. The control unit preferably includes, or is associated with, a timer, conveniently a controllable pre-programmable timer (not shown). 
     The apparatus  10  further includes a ring, or line status, detection unit  30 . The detection unit  30  is coupled to the line  15  in order to detect the presence of, in particular, an incoming or outgoing call. Conveniently, this may be achieved by monitoring the voltages or currents on the wires  16 . When the detection unit  30  detects an incoming call, it sends a signal (e.g. a monostable pulse or a repetitive pulse train) to the control unit  26  thereby alerting the control unit  26  to the incoming call. In the preferred embodiment, the detection unit  30  is configured to monitor the line  15 , to detect at least incoming calls and preferably to detect and distinguish between incoming and outgoing calls and to send a signal to the control unit  26  indicative of whether an incoming or outgoing call has been detected. This may be achieved by recognising respective signal (e.g. current and/or voltage) characteristics on the line  15 . For example, an incoming call typically produces an oscillating signal on the line  15 , whereas an outgoing call is typically preceded by a single step voltage change on the line  15  as the machine  12  transfers from an on-hook state to an off-hook state. Preferably, the detector  30  sends a signal to the controller  26  that is indicative of the signal detected on the line  15 , and the controller  26  interprets the signal received from the detector  30  in accordance with its programming. 
     The apparatus  10  may include its own power supply  32  which may take the form of one or more batteries, or an isolated AC mains derived supply. A voltage regulator  34  may also be provided to ensure that an appropriate power supply is provided to at least some of the components of the apparatus  10  (e.g. the control unit  26  and the switching device  18  in the example of  FIG. 1 ). 
     In use, the switching device  18  preferably adopts a normally closed state in which calls are allowed to be sent from and to be received by the fax machine  12 . When a first incoming call is detected by the detection unit  30  after a quiescent period (outside of the time period during which calls are allowed), the control unit  26  is notified and causes the switching device  18  to open before the incoming call can be received by the fax machine  12 . Hence, the call is prevented from reaching the fax machine  12  because the switching device  18  is open. Accordingly, the machine making the call determines that the fax machine  12  is unavailable, not answering or engaged and so terminates the attempted call. 
     The control unit  26  then causes the switching device  18  to adopt the closed state. For a predetermined, and preferably adjustable, period of time thereafter, the control unit  26  is programmed to take no action to block incoming calls. The control unit  26  may use the timer to determine the length of time for which incoming calls are allowed to reach the fax machine  12 . Hence, the control unit  26  and the timer together create an enabled time period during which the switching device  18  remains closed and incoming calls are able to reach the fax machine  12 . 
     When the detector  30  detects an outgoing call, the control unit  26  need take no action and the outgoing call is able to be transmitted. 
     In an alternative embodiment (not illustrated), the switching device  18  may be configured to adopt a normally open state, the control unit  26  being arranged to close the switching device  18  for a finite period of time after an initial call is blocked, and to close the switching device  18  whenever an outgoing call is detected. 
     In the preferred embodiment, the period of time for which incoming calls are allowed is set to be greater than the typical re-dial period for a conventional fax machine but less than the typical re-dial period for a typical automated “spamming” or junk fax machine. For example, conventional fax machines typically re-dial an engaged or unavailable number after approximately 3 minutes. Accordingly, the control unit  26  may be configured to allow incoming calls for, for example, approximately 5 minutes. Hence, when a conventional fax machine—which is assumed to be trying to send a genuine message to the fax machine  12 —re-dials the number of the fax machine  12 , the incoming call will now be received by the fax machine  12 . Similarly, if a user manually re-dials the number of the fax machine while the switching device  18  is closed, then the re-sent call will be received. However, an automated “spamming” fax machine typically re-dials after a longer period—perhaps after one or more hours. It is probable, therefore, that when the spamming machine re-dials, its call is again treated as a first incoming call after a quiescent period and is therefore blocked by the switching device  18 . The period for which incoming calls are allowed is preferably adjustable, for example for periods of between 1 and 10 minutes. 
     In preferred embodiments, once an incoming call reaches the machine  12 , the controller  26  monitors the line  15 , via the detector  30 , in order to detect the end of the call. This may be achieved by detecting a quiescent state (i.e. the absence of signal activity) on the line  15  after the incoming call is received. To avoid mis-detection of the end of a call by interpreting say a pause in the call as the end of the call, the controller is programmable to only determine that the end of a call has occurred when activity on the line as ceased for at least a pre-determined period. If an allowed call lasts longer than the period for which incoming calls are allowed, then the controller  26  may be arranged to block the next call detected after the allowed call has ended. The controller  26  may be arranged to block the next call detected after an allowed call has ended, irrespective of whether or not the period for which incoming calls are allowed has expired. 
     Referring now in particular to  FIG. 2 , a specific embodiment of the detection unit  30  is shown by way of example. The detector  30  is electrically connected to the line  15  at two of the wires  16  in order to monitor signals present on the wires  16 . The detector  30  is coupled to the controller  26  by means of opto-isolators  40  so that the detected line signals can be communicated to the controller  26  while the detector  30  is electrically isolated from the controller  26 . 
       FIG. 3  shows an alternative embodiment of an apparatus for intercepting calls, generally indicated as  10 ′. The apparatus  10 ′ is similar to the apparatus  10  with like numerals being used to indicate like parts. However, the apparatus  10 ′ employs an alternative switching device  18 ′ comprising FET (Field Effect Transistor) switches  142  rather than relay switches. The apparatus  10 ′ operates in substantially the same manner as the apparatus  10 . Either apparatus  10 ,  10 ′ may include a lamp, e.g. an LED  144 , for indicating the state of the switching device  18 ,  18 ′. 
     In  FIGS. 2 and 3 , conventional electrical and electronic symbols and notation are used to represent electrical and electronic components as will be understood by a skilled person. Any component values provided in  FIGS. 2 and 3  are provided by way of example and are not limiting to the invention. It will be understood that the specific circuits shown in  FIGS. 2 and 3  are provided as examples of how the apparatus of  FIG. 1  may be implemented and that alternative implementations are possible, as would be apparent to a skilled person. 
     In the illustrated embodiment, the switching device  18  is presented as breaking the line  15  in order to block incoming calls. It will be understood that, in alternative embodiments (not illustrated), the apparatus may be arranged to block incoming calls in any other convenient manner. For example, the apparatus may include a device for sending a signal, via the line  15 , to the sender of the incoming call indicating that the line  15  is busy or otherwise unavailable. The device may be included in the control unit, or be separate from but controlled by the control unit. Conveniently, the device is connected to the line  15  in order to place electrical signals thereon which simulate, say, a busy or unavailable condition. Alternatively, the device may be configured to transmit an audio or voice message on the line  15 , for example in a manner similar to that of a fax/telephone answering machine. Alternatively still, the apparatus  10  may include means for selectably preventing the fax machine  12  from receiving an incoming call by, for example, preventing it from picking up the call. The sending fax machine may therefore receive a signal indicating that the fax machine  12  is not answering its call. In the embodiments envisaged above, it is preferred that the apparatus may also include a switching device having the same or similar in functionality to the switching devices  18 ,  18 ′ described above. 
     In a further alternative embodiment, the apparatus may be arranged to create one or more enabled time periods which correspond to respective periods in a 24 hr clock cycle, calls being allowed to reach the device only if they are received during an enabled time period. 
     The invention is described herein in the context of facsimile transmissions but could equally be used in other applications, for example in blocking calls or texts to a telephone. 
     The invention is not limited be the embodiments described herein which may be modified or varied without departing from the scope of the invention.