Abstract:
An intercom system for use with a remote demarcation point includes a remote demarcation interface module operatively connected to the remote demarcation point, wherein the remote demarcation interface module selectively connects and disconnects with the remote demarcation point. In the system, a control module connects a subscriber telephone instrument to a remote demarcation point. The control module includes a processor module that includes processor logic operative to receive and process one or more signals, and subscriber monitor logic operative to monitor the subscriber telephone instrument activity and to provide a subscriber control signal to the processor logic. A steering relay module is operative to selectively connect and disconnect the subscriber telephone instrument to the remote demarcation point upon receipt of a steering control signal from the processor logic, wherein the steering control signal is generated by the processor module based upon the subscriber control signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit, under 35 U.S.C. Section 119(e), of co-pending Provisional Application No. 60/804,809, filed Jun. 14, 2006, the disclosure of which is incorporated by reference herein in its entirety. 
     
     FEDERALLY-SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not Applicable 
       REFERENCE TO APPENDIX 
       [0003]    Not Applicable 
       BACKGROUND 
       [0004]    This invention relates to telephone intercom systems for multiple resident buildings, and in particular, to intercom systems with non-localized points of demarcation with either single stations (concierge) or multiple stations (concierge, door attendant, valet, management office, etc.) 
         [0005]    Conventional telephone sets, i.e., those coupling to the “tip and ring” terminals of a conventional analog “local loop” of a “Plain Old Telephone Service” (“POTS”) or a PBX, typically comprise a “transmitter” (e.g., a mouthpiece or microphone), a “receiver” (e.g., a speaker or earphone), and a manually actuated “switchhook” mechanism that switches the set between an “off-hook” condition, i.e., one coupled to the local loop for signaling and communication purposes, and an “on-hook” condition, i.e., one decoupled from the local loop. The analog current-signaling technique employed in such telephones enables them to operate without need for an external power supply, since all of the electrical power needed to operate the set, 48 VDC at up to 120 mA, or 5-6 W, is supplied on the local loop by the local telephone company (“Telco”) or PBX so long as the telephone set is in the off-hook condition. However, when the set is in the on-hook condition, i.e., decoupled from the local loop, the maximum amount of power that the set can draw from the local loop is substantially limited, by FCC regulation, to 480 μW, i.e., 48 VDC at 10 μA. 
         [0006]    Telephone intercom systems facilitate internal building communication between a remote participant (or “subscriber” or “resident”) and another location (or “station”), such as a concierge, door attendant, valet, management office, and the like, without incurring charges from the telephone company. Currently there are two main types of telephone intercom systems. The first type is a “call up” telephone intercom system where the subscriber uses a telephone to provide visitors entry into the building without having to walk to the entrance and open the door. The second type is the “call up and call down” system where the subscriber not only uses a telephone to provide visitors entry into the building, but can also use the telephone to call down to another station to initiate an intercom telephone call with a limited number of door attendant/concierge/valet/management office telephones. 
         [0007]    Conventional telephone intercom systems are designed to interface with the building telephone system at the telephone company&#39;s (or “Telco”) single point of demarcation. The telephone company routes all incoming resident Telco lines to a central location, such as a telephone room, which is designated as the point of demarcation for the telephone company. Telephone intercom systems, which are considered building capital equipment, interface with the incoming resident Telco lines after the point of demarcation to allow internal building communication from the entry door telephone or concierge telephone to the subscriber telephone (call up) and subscriber telephone to the concierge telephone (call down). The telephone company&#39;s responsibility for telephone service ends at the point of demarcation. 
         [0008]    Current trends in construction of new multiple resident buildings include “fiber to residence,” i.e. new points of demarcation are now extended to each floor and/or all the way to each individual apartment or condominium. As a result, the telephone company is no longer bringing all of the Telco lines into the building to a single point of demarcation, but instead routing the lines to multiple remote demarcation points. Conventional telephone entry systems are unable to work in the “fiber to residence” building designs without running multiple sets of twisted pairs from the residence to the telephone room, and do not provide an interface with the Telco/resident telephone line non-localized points of demarcation. 
         [0009]    As the telephone intercom system can no longer complete its interface in the local telephone room, a need exists for a system that provides an intercom control unit in a centralized location that can interface with the resident&#39;s telephone through a remote demarcation interface module connected to the intercom control unit by a single twisted two wire pair. 
       SUMMARY OF THE INVENTION 
       [0010]    As used herein, the terms “the invention” and “the present invention” shall encompass the specific embodiments disclosed herein, as well as any and all equivalents that may suggest themselves to those skilled in the pertinent arts. 
         [0011]    In one aspect, the present invention is an intercom system for use with a remote demarcation point. The intercom system includes a remote demarcation interface module. The remote demarcation interface module is operatively connected to the remote demarcation point wherein the remote demarcation interface module selectively connects and disconnects with the remote demarcation point. 
         [0012]    In a second aspect, the present invention is a control module to connect a subscriber telephone instrument to a remote demarcation point. The control module includes a processor module to receive and process one or more signals, a subscriber monitor logic to monitor the subscriber telephone instrument activity and provide a subscriber control signal to the processor logic. The control module further includes a steering relay module to selectively connect and disconnect the subscriber telephone instrument to the remote demarcation point upon receipt of a steering control signal from the processor logic. The steering control signal is generated by the processor module based upon the subscriber control signal. 
         [0013]    In a third aspect, the present invention is a method to connect a subscriber telephone instrument to a remote demarcation point and an intercom control unit. The method includes the steps of monitoring the subscriber telephone instrument activity and providing a subscriber control signal to a processor logic; and generating a steering control signal based upon the subscriber control signal to selectively connect and disconnect the subscriber telephone instrument to the remote demarcation point and the intercom control unit. 
         [0014]    A better understanding of the above and many other features and advantages of the invention may be obtained from a consideration of the detailed description of the invention below, especially if such consideration is made in conjunction with the appended drawing. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a block diagram of a telephone intercom system in accordance with a preferred embodiment of the present invention; 
           [0016]      FIG. 2  is a block diagram of a remote demarcation interface module in accordance with a preferred embodiment of the present invention; and 
           [0017]      FIG. 3  is a schematic diagram of the remote demarcation interface module of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    A block diagram of a telephone intercom system  100  in accordance with a preferred embodiment of the present invention is illustrated in  FIG. 1 . The system  100  can be applied to both “call up” systems and “call up and call down” systems. 
         [0019]    Cable and fiber technology  101  is being increasingly used to provide data  103 , video  105  and voice services to subscribers. By using cable and fiber technology, the point of telephone service demarcation is no longer located in one central location and remote points of demarcation are now located on each floor and/or in each individual apartment or condominium. Since there is no longer one central location for demarcation, a remote demarcation point  106  is needed for each subscriber. If remote demarcation points are located on each floor, cable must be supplied to each apartment or condominium on each floor to the remote demarcation point from a remote demarcation interface module (“RDIM”)  104  provided for each subscriber. 
         [0020]    As conventional telephone intercom systems are designed to interface centrally with the telco/resident telephone lines at a single telephone company point of demarcation, an intercom control unit  109  is necessary in a centralized location to supervise all the remote non-localized demarcation points  106 . The intercom control unit  109  processes all calls between the subscriber and remote stations and interfaces with each subscriber&#39;s telephone through a remote demarcation interface module  104 . In the preferred embodiment of the present invention, the intercom control unit  109  is a Model 6000R manufactured by Trigon Electronics, Inc., of Corona, Calif. All telco/resident phone lines are connected to the intercom control unit  109  via a remote demarcation interface module  104 . The intercom control unit  109  processes the calls between the entrance to the building and the subscriber. The telephone company is not involved, so the subscriber does not incur any charges. 
         [0021]    A single two-wire twisted pair  107  connects the intercom control unit  109  to the remote demarcation module  104  on a per subscriber basis, and it is used to transmit data to the intercom control unit  109 . The wire pair  107  is a mirror image of the subscriber lines, such that when the subscriber goes off hook, the remote demarcation module  104  reflects this condition to the intercom control unit  109  by also going off hook (creates loop-start current path). 
         [0022]    Remote demarcation interface modules  104  can be installed at any point phone line service ends in a “Plain Old Telephone Service” (“POTS”)  102  type service jack, such as a conventional RJ11 2-wire female phone jack. When installing a remote demarcation interface module  104 , a POTS Tip/Ring signal is first passed through the remote demarcation interface module  104  and then transmitted to subscriber phones  108 . This allows the remote demarcation module  104  to act as a splitter providing dual service (telco and intercom) to one subscriber and preventing a clash of controls, signals and power, which would normally occur when the intercom control unit  109  and the telco service both control the subscriber&#39;s phone. 
         [0023]    The intercom control unit  109  passively monitors the subscriber&#39;s phone, i.e. without the telco service, and supplies power to the phone for dialing purposes by supplying power to the remote demarcation interface module  104  so that it is in a stand-by-mode. If the remote demarcation interface module  104  determines that there is no telco power, the remote demarcation module  104  supplies power to the subscriber&#39;s phone and disconnects the telco service at the remote demarcation module  104 . If the telco service returns, the remote demarcation interface module  104  restores the telco power to the subscriber phone and resumes passive monitoring. 
         [0024]    During passive monitoring, if the subscriber goes off hook and draws operational loop start current, then the remote demarcation interface module  104  disconnects the telco service. If the subscriber dials a number, the dialing tones are transferred to the intercom control unit  109  as if it has a real connection to the subscriber phone. Thus, the remote demarcation interface module  104  generates a mirror image of the subscriber phone to the intercom control unit  109  which is interpreted as the real subscriber&#39;s phone. If a call is placed to the subscriber, via the intercom control unit  109 , that call returns a busy signal to the intercom user, such as the Concierge, if the subscriber&#39;s line is currently in use on a regular telco call. If the subscriber is not using the phone, the ring signal to the remote demarcation interface module  104  temporarily disconnects the telco service and allows the intercom ring signal to reach the subscriber phone directly. After the call is answered by the subscriber and completed when the subscriber hangs up, the remote demarcation interface module  104  resumes passive monitoring of the subscriber&#39;s phone and service. 
         [0025]    The subscriber&#39;s phone service does not detect the remote demarcation module  104 , as the impedance or capacitance is not impacted. However, due to the added load, the available voltage will drop by approximately one volt and will appear as an additional parallel resistance of more than 5.1 Megohms. This voltage drop has no effect on the system  100  as the telco supplies 48V to the system  100 , and a typical phone only needs 7-10V. Telco lines are current-regulated to provide only the needed power; otherwise all the extra voltage will be wasted in the form of heat. 
         [0026]    To utilize the telephone intercom system  100  of the present invention, a subscriber presses a key or a series of keys on a telephone, creating a Dual Tone Multi-Frequency (“DTMF”) signal. A copy of the DTMF signal is transmitted to the intercom control unit  109  on the wire pair  107 , providing the intercom control unit  109  with the status of the subscriber (i.e. whether or not the subscriber is on the telephone) on a per-subscriber basis. 
         [0027]    Turning to  FIG. 2 , a block diagram of the internal structure of the remote demarcation interface module  104  of  FIG. 1  is shown. The remote demarcation interface module  104  connects a subscriber to a remote demarcation point  106 . A remote demarcation point (RDP) power monitor  120 , connected to the remote demarcation point  106 , monitors the output voltage of the remote demarcation point  106  via a 5.1 Megohm resistor R 9  ( FIG. 3 ). This output voltage is then transmitted to a microprocessor module  122 , via a status line  123 , providing the micro-processor module  122  with the status of the subscriber, i.e. if the subscriber is on the telephone. 
         [0028]    A subscriber monitor  124 , connected to the subscriber phones  108 , monitors the subscriber hook loop current status, DTMF dialing and ring signal. The hook loop current status indicates if the subscriber is on the telephone. Lifting a phone off the cradle closes the hook switch, thus completing the loop for power to flow using the phone as the power load. If there is a flow of current, the phone is in use. If there is not a flow of current, the phone is not in use. 
         [0029]    A first small opto-coupler  130  ( FIG. 3 ), such as a H11AA1, within the subscriber monitor  124  reads the subscriber hook loop current status, DTMF dialing, and ring signal, and it transmits this data to the microprocessor module  122  for analysis via a status line  125 . With this information, the microprocessor module  122  determines if the subscriber is on the phone, and thus enables the mirror of the subscriber actions to the intercom control unit  109  via the wire pair  107 . The mirror functions require more power than just passive monitoring. This additional power is supplied by a 2.2 F “super cap” C 5  ( FIG. 3 ) in a power storage cell  127  that has been trickle-charged (as described below) from the intercom Loop-Start voltage. 
         [0030]    A power control block  126  is connected to the microprocessor module  122  and trickle charges a power storage cell  127  in the remote demarcation interface module  104  using the 24V Loop-Start voltage. The 24V Loop-Start Voltage is power made available for the subscriber&#39;s phone to enable the phone to operate, such as the generation of dial tones and the generation of DTMF signals for dialing. In the case of a remote demarcation interface module  104 , the 24V Loop-Start Voltage supplies power to operate a microprocessor  122   a  (see  FIG. 3 ) in the microprocessor module  122 , and to trickle charge the power cell  127 . The loading must be kept very low, so as not to be mistaken for all off-look loop-start power draw greater than 15 mA. The power control block  126  receives a mirror image of the data on the subscriber lines, such that when the subscriber goes off hook (i.e. the subscriber is on the telephone), the microprocessor  122   a  instructs the power supplied from the intercom control unit  109  to be likewise loaded. 
         [0031]    A steering relay  128 , such as a G6KU-2F5 DPDT relay, is connected between the RDP power monitor  120  and the subscriber monitor  124 . The steering relay  128  is controlled by the microprocessor module  122  through a control line  129 . If the microprocessor module  122  determines that the remote demarcation point  106  is powered down, out of service or simply doesn&#39;t exist, the steering relay  128  switches the subscriber directly to the intercom control unit  109 , via the power control block  126 . The intercom control unit  109  communicates with the subscriber directly and provides the service voltage (i.e., the voltage required to power the phone after a call has been started, that is, after dialing has begun) to the subscriber phone  108 , so that the subscriber can dial a number via DTMF. The DTMF number dialed by the subscriber is received by the intercom control unit  109 , either as a mirror of the actual status of the subscriber or directly. 
         [0032]    Specific number sequences are preprogrammed into the system for the subscriber to use. If the subscriber dials a specific pre-defined number sequence, such as 48# which indicates a call back request, the intercom control unit  109  registers this as a call back request, and the request is put into a queue for processing. For example, a subscriber may request that the manager of the units call back the subscriber when the subscriber is off the telephone. Once the micro-processor module  122  of RDIM of the subscriber detects that the subscriber is no longer on the telephone, which status is also visible to the intercom control unit  109  and the microprocessor module of RDIM of the manager telephone is also free (i.e. Off Hook), the intercom control unit  109  initiates the process to connect the subscriber to the manager. First, the intercom control unit  109  initiates a call to the Manager. When the Manager answers the internal call from the intercom control unit  109 , the intercom control unit verifies whether the subscriber is still free to answer the call. If the subscriber is not free, a busy signal is sent to the Manager, and the request is placed back into the queue. This may happen if a subscriber receives a call on the subscriber&#39;s “normal” (i.e., telco) service immediately after placing a request for call back. When the subscriber has completed the normal call, the system will again attempt to make a connection as outlined above. If the subscriber line is free, a ring signal is sent to the remote demarcation interface module  104  of the subscriber, from the intercom control unit  109 , which, in turn, causes the subscriber&#39;s phone to ring. 
         [0033]    The remote demarcation module  104  can ring the subscriber&#39;s telephone in one of two ways. First, if the RDP power monitor  120  is not producing Loop Voltage, the steering relay  128  allows a Ring Signal Voltage directly to the subscriber, from the intercom control unit  109 , resulting in the subscriber&#39;s phone ringing. Second, if the RDP power monitor  120  is producing Loop Voltage from the intercom control unit  109 , but is currently idle, the presence of the Ring signal directs the microprocessor module  122  to switch the steering relay  128  to the subscriber and monitor the call in progress using the stored energy in the power storage cell  127  for the duration of the call. When the call is terminated, the microprocessor module  122  restores the steering relay  128  back to normal subscriber service, if present. 
         [0034]    Turning to  FIG. 3 , a schematic diagram of a specific exemplary embodiment of the remote demarcation interface module  104  of  FIG. 2  is shown. A subscriber&#39;s phone  108  is connected to the remote demarcation interface module  104  via a conventional RJ11 telephone jack  108   a . A first line of the jack  108   a  is connected to a first input pin of the first opto-coupler  130 , such as a H11AA1, and to a first input of a relay  132  and a second input pin of the first opto-coupler  130  through a 100 ohm resistor R 1 . The second line of the jack  108   a  is connected directly to a second input of the relay  132 . As discussed previously, the first opto-coupler  130  reads the subscriber hook loop current status, DTMF dialing, and the ring signal, and it transmits this data to the microprocessor  122  for analysis via the status line  125 . With this information, the microprocessor  122   a  determines if the subscriber is on the telephone, if the subscriber has entered a predefined sequence, and what request is associated with the predefined sequence. 
         [0035]    A second opto-coupler  134 , such as a H11AA1, is connected to the microprocessor  122   a  and monitors the output voltage of the remote demarcation point  106  via the 5.1 Megohm resistor R 9 . This output voltage is then transmitted to the microprocessor  122   a , via status line  123 , providing the microprocessor  122   a  with the status of the telco service, i.e. if the subscriber service is active. When the subscriber goes off hook, the microprocessor  122   a  transmits a signal to a synthetic hook switch  136 , such as a HT18, which in turn sends a signal to an AC bridge  138 , causing power from the intercom control unit  109  to be loaded. The intercom control unit  109  and the AC input side of the AC to DC bridge  138  are also connected to the relay  132 . When the relay  132  is switched to a first position, the subscriber&#39;s telephone can be used for internal communications, and when the relay  132  is switched to a second position, normal subscriber service is returned. 
         [0036]    The AC to DC bridge  138  provides polarity protection to the power circuits. A 0.47 μF capacitor C 3 , a 470 μF capacitor C 4 , and a MUE5852 transistor T 1  provide a power path that opens during a ring signal so as not to present a ring load to the ring signal causing a misinterpretation of a loaded phone (i.e. the phone has been answered) by the intercom. The 0.47 μF capacitor C 3  passes the change in voltage to a 47 kilohm resistor R 4  and the base of the MUE5852 transistor T 1 . This makes the base voltage equal to the emitter voltage, thus pinching off the transistor T 1 . A IN4004 diode D 2  prevents back flushing the charge of capacitor C 4  back into transistor T 1 . This same power path trickle charges, via a 1 kilohm resistor R 5  and the diode D 2 , to the capacitor C 4 , limited by a 12V Zener diode D 3  to 12 Volts. Thus the difference from 24V to 12V limited by the 1 kilohm resistor R 5  becomes 12 mA and is below the threshold of the intercom hook-loop current. 
         [0037]    A voltage regulator  142 , such as an MIC52135V, drops the 12V to 5.3V using a IN5819 diode D 4  as an offset. A 5.3V diode D 5 , such as a IN5819, drops the extra 0.3V to supply 5V to all powered components, and trickle charges the “super cap” C 5 , rated at 2.2 Farads at 5.5V. When the lines  107  are loaded down below 12 volts during an off-hook condition generated either by the subscriber phone directly or by the function of the synthetic hook switch  136 , then the diode D 2  prevents any back flush of power into the service loop at the intercom control unit  109 . During these brown out conditions (and during the ring signal from the intercom) the super capacitor C 5  can provide full power for up to 24 hours. It should be noted that it only has to supply power for a few minutes during an intercom call on the average. In fact, the micro-processor  122   a  only draws normal power when it “wakes up” at the onset of a subscriber call (dialing period), limited to the first 10 second interval in which a subscriber must dial before the microprocessor  122   a  returns to a semi-sleep mode and extremely low power draw, until the subscriber recycles by hanging up the phone and lifting it again for a fresh dial tone. 
         [0038]    As described above, the power control block  126  is connected to the microprocessor module  122  and is used to trickle charge the power storage cell  127  connected to the power control block  126  using the 24V Loop-Start voltage. In this specific exemplary embodiment of the invention, the internal circuitry of the power control block  126  comprises a 0.1 μF capacitor C 1 ; three 47 kilohm resistors R 2 , R 3 , R 4 ; a 5V Zener diode D 1 ; a 0.1 μF capacitor C 2 ; a 0.47 μF capacitor C 3 ; a MUE5852 transistor T 1 ; a 1 kilohm resistor R 5 ; and a IN4004 diode D 2 . 
         [0039]    In the aforementioned specific exemplary embodiment, the internal circuitry of the power storage cell  127  comprises a 5.3V diode D 6  (which may be IN5819 diode); a 1 kilohm resistor R 6 ; and the 2.2 F “super” capacitor C 5 . 
         [0040]    Continuing with the description of the specific exemplary embodiment illustrated in  FIG. 3 , the internal circuitry of the RDP power monitor  120  comprises a 2N2222 transistor T 2 ; a 15 kilohm resistor R 7 ; two 5.1 megohm resistors R 8 , R 9 ; the second opto-coupler  134 ; and a 5V DC power supply. The resistor R 9  provides a leakage path that lights an LED (not shown) inside the second opto-coupler  134 . This conducts a very small current flow inside the second opto-coupler  134  from a 5V DC source  139  to the resistor R 7 . The transistor T 2  amplifies this flow to a logic level from ground via the transistor T 2  to the pull up voltage value of the resistor R 8 , which is also 5V DC. 
         [0041]    The steering relay  128  ( FIG. 2 ) is a latch type relay and only requires power to change states. This power comes in the form of a pulse of 10 milliseconds delivered from the microprocessor  122   a  via the control lines (coil pins  1  and  8  of the relay  128 ). 
         [0042]    The internal circuitry of the subscriber monitor  124  comprises three 47 kilohm resistors R 10 , R 13 , R 14 ; a 0.1 μF capacitor C 7 ; the first opto-coupler  130 ; the 100 ohm resistor R 1 ; a 1 kilohm resistor R 11  connected to a 12V DC power supply; a 100 kilohm resistor R 12 ; a 100 pF capacitor C 6 ; and a third 2N2222 transistor T 3 . The first opto-coupler  130  passes the subscriber current through it and is biased via the resistor R 1  to operate at approximately 1V. This dramatically reduces the gain well below the diode knee curve of an LED. The gain of the first opto-coupler  130  is further reduced by bias on the collector and emitter in a feedback loop composed of the resistors R 10 , R 11 , R 12  and the transistor T 3 . 
         [0043]    An AC signal (DTMF) is allowed to by-pass this DC gain reduction via the capacitor C 6 . The emitter of the first opto-coupler  130  is biased at about 6V DC with the DTMF riding on top with a typical signal level of 200 mV peak-to-peak. The oil/off nature of this bias is sub-divided to 0V as “off” and 3V DC as “on” (subscriber active) via the resistors R 13  and R 14 . This sub-divided logic level is fed to the microprocessor module  122  as TRUE/FALSE logic called hook status. The DTMF tones are passed through the capacitor C 7  for later amplification. 
         [0044]    The internal circuitry of the microprocessor module  122  comprises the microprocessor  122   a ; the synthetic hook switch  136 , such as an HT18, with a 270 ohm resistive load  151 ; an analog amplifier  150 , such as an LM4819 to amplify any DTMF signals; a first 20 kilohm resistor R 15 ; a second 20 kilohm resistor R 16 ; a 33 pF band limiter capacitor C 9  in parallel with the second 20 kilohm resistor R 16 ; a 1.0 μF anti-pop suppressor capacitor C 8 ; two 47 kilohm resistors R 2 , R 3 ; two 0.1 μF capacitors C 1 , C 2 ; and a 5V Zener diode D 1 . 
         [0045]    The microprocessor module  122  is composed of all control signals described above and also includes the microprocessor  122   a , such as an Atnels AT Tiny 25, the synthetic hook switch  136 , and the low power analog amplifier  150  for boosting the DTMF signal strength back to 2V peak-to-peak. The 270 ohm resistor  151  across the synthetic hook switch  136  acts as an artificial phone load of 270 ohms when the switch  136  is instructed to be “on” by the microprocessor AC control logic. The DTMF signal amplifier comprises the resistors R 15  and R 16 ; the band limiter capacitor C 9 , the analog amplifier  150 ; the anti-pop suppressor capacitor C 8 , and the capacitor C 1  that drives the artificial 270 ohm load with AC signal (DTMF). Also, one leg of the steering relay logic is used for enabling and disabling the amplifier  150  when its use is not required. Lastly, ring is detected from the intercom control unit  109  via the capacitor C 2 , which passes the AC signal to a voltage divider made from the resistors R 2  and R 3  and limited to 5V via the Zener diode D 1 . 
         [0046]    Additionally, it will be appreciated that it is possible to replace substantially all of the discrete components of the remote demarcation interface module described with an application-specific integrated circuit (“ASIC”) microprocessor capable of operating in a very-low-power “standby” or “sleep” mode. Other such modifications will also suggest themselves to those of skill in the art in light of the disclosures contained herein. In the drawings, in addition to the reference numerals, various labels and signals have been shown. It is to be understood that various labels and signals are shown to assist in following the detailed description of the figures and are not intended to limit the scope of the invention. 
         [0047]    While the present invention is described above with respect to what is currently considered its preferred embodiments it is to be understood that the invention is not limited to that described above. To the contrary, the invention is intended to cover various modifications and equivalent arrangements within the spirit and scope of the appended claims.