Abstract:
An apparatus ( 40 ) and method for switching a customer-premises telephone line ( 36 ) between a plurality of local telephone networks ( 35 ). The local telephone networks may have different electrical and operational characteristics. Using less than 100 micro-amperes of current from the telephone networks, the apparatus ( 40 ) requires no external power and performs its tasks without interfering with the normal operation of the telephone networks including test equipment, terminal equipment, data transmission on the telephone line and test equipment.  
     The method involves monitoring electrical signals on both local telephone networks ( 35 ) and using this information to assign a weight to each network. The customer-premises telephone line ( 36 ) is switched to the telephone network having the highest weight. The advantages are the elimination of a service call by a technician to manually switch the customer premises telephone line ( 36 ), equal access by both service providers to the switch and a seamless interface to the telephone networks.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application clams priority from U.S. Provisional application Ser. No. 60/350,981, filed Jan. 25, 2002, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This Automatic telephone Line Switch (ATLS) relates to a telecommunication switch designed to switch a customer-premises two-wire telephone line between one of a plurality of local telephone networks owned by independent telephone service providers. The switching is performed at the subscriber&#39;s end of the network without the intervention of an on-site service technician.  
       BACKGROUND OF INVENTION  
       [0003]     Traditionally most local telephone networks belonged to the same telephone company. This company was broken up into several Regional Bell Operating Companies (RBOC). These telephone service providers are now called Local Exchange Carriers (LEC). Every subscriber that has local (i.e.: not long distance, not cellular) telephone service is connected to a local telephone line  32  as shown in  FIG. 1 . The point of origin of the local telephone line is the LEC equipment  33 . At the point of origin  33 , the local telephone line  32  can be switched between different types of equipment or network interfaces using a switch matrix  30  of the type described by Kellock U.S. Pat. No. 6,259,676,B1, dated Jul. 10, 2001 or using the method described by King, US Patent Application U.S. 2001/0040956 A1 dated Nov.,  15 ,  2001 . The switch matrix  30  can be an automatic device of the type described by Suzuki et al., U.S. Pat. No. 5,790,651, dated Aug. 4, 1998, or a manual connection block as described by Napiorkowski et al., U.S. Pat. No. 5,570,422, Dated Oct. 29, 1996. All the local telephone equipment from the local telephone switch  22  up to the demarcation point  34  shown in  FIG. 1  belongs to a single service provider having one centralized network maintenance and control system  23  also called an Operation System (OS). The term local telephone network is used throughout this document to designate the equipment, the facilities and the operating system. The demarcation point  34  is the interface point between the customer-premises telephone line  36  and the service provider local network  35 . The term Network Terminating Interface (NTE) is often a synonym of the demarcation point  34 . To simplify the diagram, a telephone symbol  38  is used to represent any customer-premises telephone equipment in  FIG. 1  to  4 .  
         [0004]     In the early 1990&#39;s, LECs started competing with other LECs by purchasing facilities (i.e. telephone lines) from selling LECs.  FIG. 2  shows a customer-premises telephone line  36  connected to a local telephone line  32  that belongs to a LEC but is purchased by another LEC. As can be seen from  FIG. 2 , switching local telephone lines  32  with attached customer-premises lines  36  at the service provider end of the network can easily be accomplished by prior art equipment and methods  28 ,  30  described above or by maintenance personnel.  
         [0005]     As the telecommunications industry evolved, Competitive Access Providers (CAPs) emerged to compete with LECs to offer subscribers local telephone service. The CAPs extended their telecommunication networks from the Local telecommunication Switch  22 A up to the demarcation point  34 A.  FIG. 3  shows a subscriber that is serviced by two telephone service providers. Each service provider has a local telephone network  22  to  34  and  22 A to  34 A that terminates at demarcation points  34  and  34 A at the subscriber&#39;s premises  39 .  
         [0006]     This new configuration creates a problem involving an expensive service call by maintenance personnel that wipes out any benefits to consumers afforded by competition in the local telephone industry.  
         [0007]     When a subscriber changes from one service provider to the other, the telephone line  36  has to be physically disconnected from demarcation point  34  and re-connected to demarcation point  34 A. For many reasons, it is not possible to connect both telephone lines in parallel  37  at the subscriber end with prior art equipment  30  and  30 A such as Kellock or by using a the method described by King. One major reasons is that the local networks of the two service providers often have different electrical characteristics, some model of Network Elements (NE)  26 A used by CAPs have a 24 Volts DC battery voltage with a local ground  29 A while the LEC network may have a 48 volt DC battery voltage that is grounded at the originating end of the network  29 .  FIG. 3  illustrated a frequent network configuration where the LEC has a very long local telephone line  32  between its local switch  30  and the demarcation point  34  while the CAP has a short local telephone line  32 A because the CAP has placed the Network Element  26 A close the demarcation point  34 A. King recognizes that telephone systems are not designed to operate with two lines in parallel in paragraph (0037) page 3 and goes on to state that maintenance personnel is still required although at a more convenient time.  
         [0008]     While King claims the selling LEC gives control of the connection process to the purchasing LEC,  FIG. 5 , block S 12  of his patent shows the purchasing LEC requesting a confirmation from the selling LEC effectively giving the selling LEC the capability to block or delay the transfer of the subscriber. While LECs tent to cooperate with each other, cooperation between a CAP and a LEC is less frequent. From a business perspective, the problem is easily understood; LECs selling and buying from each other are in a win-win situation. On the other hand, a CAP completely removes the subscriber and the revenue stream, leaving the LEC with an unused facility that still requires maintenance.  
         [0009]     A telecommunications switch as described by Nolde, U.S. Pat. No. 5,920,615, dated Jul. 6, 1999 is also not feasible to eliminate service calls because it is designed to switch a plurality of normal communication apparatus on a single local telephone line using four wires. It does not take into account the requirement of multiple and electrically different local telephone networks as described above. In addition a Nolde-type master-slave system does not solve the equal access issues.  
         [0010]     Powering equipment to switch telephone lines at the Demarcation Points  34  and  34 A is also a serious problem not envisioned by any prior equipment. A LEC will not accept a piece of equipment in its network that is powered by local power  27 A (often used by CAP service providers) while it has centralized diesel and battery backup facilities  27  with different, sometimes better, capabilities. This eliminates prior art equipment such as Meeske, U.S. Pat. No. 6,415,022 B1, dated Jul. 2, 2002. The Meeske equipment also adds tremendous complexity to the network. Each CAP and LEC would have to keep track of this equipment and its configuration in multiple locations. Errors of one company in programming such equipment could result in loss of service to a competitor&#39;s subscriber.  
         [0011]     While using local AC power is not an option, using the telephone line power to operate equipment at the demarcation points  34  and  34 A poses serious problems because that power is intended to operate customer-premises equipment such as telephones, fax machines, modems and CallerID devices that rely on the power available from the local telephone line such as described by Ninh, U.S. Pat. No. 6,212,274 B1, dated Apr. 3, 2001. The problem is compounded by maintenance equipment used by the service providers such as equipment described by Liu, U.S. Pat. No. 6,266,395 B1, dated Jul. 24, 2001.  
         [0012]     It is an objective of this invention to solve the problems described above in a way defined in the independent claims.  
       BRIEF SUMMARY OF THE INVENTION  
       [0013]     The automatic telephone line switch (ATLS) is a device to automatically switch a customer-premises telephone line between a plurality of local telephone networks belonging to different service providers without the intervention of an on site technician. The plurality of telephone networks may have different electrical and operational characteristics. The switching is done at the customer end of the local telephone network. The ATLS performs its tasks while drawing less than 100 microamperes of current from the local telephone networks, thus requiring no external power. The ATLS performs its tasks without interfering with the normal operation of the telephone networks including terminal equipment, data transmission on the telephone line and test equipment. By monitoring signals on both telephone networks such as line voltage, dialtone, ringing, off-hook, CallerID, DTMF and tone, the ATLS performs an arbitration function to determine which telephone network should be connected to the customer-premises telephone line. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]     These drawing represent non limiting examples of preferred embodiments of the Automatic Telephone Line Switch (ATLS), in which like reference numerals represent similar parts through the several views of the drawings.  
         [0015]      FIG. 1  Shows a prior art single service provider local telephone network.  
         [0016]      FIG. 2  Shows a prior art dual service providers sharing a single local telephone network.  
         [0017]      FIG. 3  Shows a prior art dual service providers with separate and independent local telephone networks.  
         [0018]      FIG. 4  is a connection diagram of the ATLS.  
         [0019]      FIG. 5  is a block diagram of the preferred embodiment of the ATLS.  
         [0020]      FIG. 6  is a detailed schematic of the Line Interface circuit.  
         [0021]      FIG. 7  is a schematic and a block diagram of the Common Control Circuitry.  
         [0022]      FIG. 8  is a software block diagram.  
         [0023]      FIG. 9  is an alternate embodiment of the ATLS with dual MCUs.  
         [0024]      FIG. 10  is an alternate embodiment of the ATLS with connections to a plurality of networks. 
     
    
     DETAILED DESCRIPTION  
       [0000]     ATLS Network Connection  
         [0025]     The connections between the ATLS  40 , the local networks and the customer-premises telephone line are shows in  FIG. 4 . The customer-premises telephone line is connected to connector  44  while the LEC network is connected to  42  and the CAP network is connected to  46 . Connector  66  is used to program the central processor  162 .  
         [0000]     Detailed Block Diagram  
         [0026]     A more detailed block diagram of one embodiment of the ATLS is shown in  FIG. 5 . The latching relay  58  has two coils  48  and  48 A. The side B line interface  62  activated coil  48  to force relay  58  to toggle and establish a connection between connector  42  and  44 . Conversely the Side A line interface  62 A activated coil  48 A to force relay  58  to toggle and establish the connection between connector  44  and  46 . Protection  50  is a combination of an over-voltage and current limiting circuit to protect relay  58  from transient that may be present on the telephone line at  42 . This protection is designed to pass, without distortion, high frequency data signals. Protection  50  also includes provisions for a distinctive impedance signature to enable telephone line test equipment used by LECs to detect the presence of the ATLS.  
         [0027]     The side B line interface circuit  62  shown in  FIG. 6  is identical to the SideA circuit  62 A. A description of the overall strategy of reducing the current consumption of this ATLS is necessary to understand the circuitry. Ninh, page 5 lines  5  to  18  of his patent, describes extracting between 367 and 1,960 milliwatts from the telephone line in the off-hook state. The ATLS uses between 288 and 2208 microwatts. The power requirement of the ATLS are close to 1,000 times less than prior art described in Ninh and require an innovative technology not foreseen by Ninh, Ben-David, US Patent Application 2002/0015489, dated Feb. 7, 2002 or others.  
         [0000]     Description of Line Interface  62  of  FIG. 6   
         [0028]     A high impedance line interface is composed of resistors  70 , Diode Bridge  72 , capacitor  74  and zener  76 . The four identical resistors  70  have total impedance greater than one meghoms. The circuit is protected from high voltage transients without requiring bulky current limiting and voltage clamp devices used in prior art equipment. A high voltage spikes present at  52  will be evenly distributed among the equal value resistors  70  and blocked while dissipating very little energy. This is one of many important benefit of using a very high impedance telephone line interface. In addition, test equipment and Asymmetric Digital Subscriber Line (ADSL) data transmission equipment used by LECs is not adversely affected by the presence of the ATLS.  
         [0029]     Complimentary PNP  84 P and NPN  84 N transistors with good micro-amp current gain are used for unijunction circuits  84  and  84 A. This innovative design eliminates the drawbacks of prior art such as Stein, U.S. Pat. No. 3,882,421, dated May 6, 1975, where conventional unijunction transistors tend to latch up when used in circuits where the gate impedance is greater than one meghom. The gate impedance is the parallel combination of resistors  88  and  90  and of resistors  102  and  104 , both are greater than 2 meg-ohms while the charging resistors  80  and  100  are over 20 meg-ohms. The zener diode  94 , used in an unconventional way below its minimum reverse current, acts as a variable voltage zener.  
         [0030]     A line monitoring circuit detects the line status (on-hook, off-hook, ringing and 60 Hz noise) and communicates this information to the Micro-Controller Unit (MCU)  162  by pulsing it at varying frequencies through isolator  61  to maintain line-to-line isolation. This voltage to frequency circuit is embodied with components  80 , 82 , 84 , 86 , 88 , 90 , 92  and  94 . A watchdog circuit discharges capacitor  95  into relay coil  48  and delivers V 2  CV 2  of energy to switch the latching relay  58  to its side if the common control circuitry  64  does not reset it periodically through isolator  60 .  
         [0000]     Description of Common Control Circuit  64   
         [0031]     The common control circuitry  64  is connected to  44  through  56  to draw its power from the network currently connected to the customer-premises telephone line. It includes a line interface and an MCU with peripherals as shown in  FIG. 7 . The Line interface of  FIG. 7  uses a network similar to  FIG. 6 , embodied by components  122 , 124 , 126 , 128  and  130 . The capacitors  120  are added to provide a path for Alternating Current (AC) signals including but not limited to tones, ringing CallerID and dialtone. A porting of all AC and DC signals present at  56  are extracted at point  138 . Diode  142  prevents any DC present on capacitor  152  from feeding back to  138 . The low voltage circuitry of the MCU requires a power supply that can provide a constant voltage output  156  while the input  56  varies from less than 3 to more than 100 volts. This is achieved using a high voltage N-channel depletion mode (normally-on) transistor  144  in combination with a low voltage micro-amp quiescent current voltage regulator  154 . Gate  146  of transistor  144  is connected to output  156  of regulator  154  with resistor  148  while the source of transistor  144  is connected to the input  150  of regulator  154 . The voltage difference between nodes  150  and  146  will rise until the gate-to-source turn-off voltage is reached and transistor  144  turns off. The input to output differential voltage of regulator  154  must be less that the minimum gate-to-source turn-off voltage of transistor  144 . Transistor  144  dissipates little energy because of high impedance front-end resistors  122  and  124 . Capacitors  152  and  158  are chosen for their low leakage current and provide energy storage to power the MCU circuitry while the telephone line at  42  or  46  is temporarily disconnected because of maintenance activities or power failures. Line interface circuits  62 ,  62 A, and common circuitry  64  were designed not interfere with ADSL transmission or test equipment such as described by Liu. Very eliminating the need for filters often placed in series with telephone equipment that has prior art circuitry not compatible with ADSL technology.  
         [0000]     Description of MCU  162  and Associated Circuitry  
         [0032]     One embodiment of the MCU  162  and associated circuitry is shown in  FIG. 7  (CONTINUED). The signal  138  is feed to amplifier and filter  166  who&#39;s output  168  is connected to an analog to digital converter input  169  of MCU  162 . Input  168  is the line voltage, dialtone, ringing and other tones input to MCU  162 . The CallerID detector is an interface circuit that enables MCU  162  to receive Frequency Shift keying signals used in voiceband data transmissions. It is embodied by feeding signal  138  to bandpass filter  174  who&#39;s output  176  is connected to phase-lock-loop input  173  of MCU  162 . An output  178  of the MCU  162  provides the means to send tones back to the telephone line through  138 . To save power, amplifier  166  is turned on with control signal  164  only when required by MCU  162 . MCU output  172  performs the same function for amplifier  174 . Regulator output  156  is the source of power for MCU  162 . To increase accuracy during measurements of the voltage at point  138 , transistor  144  is turn off by output  170 F of MCU  162 , connected to point  146 . Very short pulses from output  170 A are used to activate Light Emitting Diode  163  thus conserving energy. Digital inputs and outputs  170 B to  170 E are connected to isolators  61 ,  61 A,  60  and  60 A. The MCU  162  has a low voltage reset circuit  165  to restart the MCU if the line voltage drops two low, a watchdog circuit  167 , FLASH memory  179  enabling in circuit programming through connector  66  and internal EEPROM  175  to store system variables. These internal circuits can be embodied in external components.  
         [0000]     Description of the Software  
         [0033]     The software method used by the hardware embodiment to switch the telephone lines is shown in  FIG. 8 . The software is designed using modular tasks that can be added or deleted to configure the functionality of the ATLS as required. Tasks that are conditional on the side of the switch are suspended when the switch is not on their side. A single bit flag, SideA/SideB, is used to keep track of the switch side.  
         [0034]     The MCU starts execution at step  200  when power is applied. In task  202  the MCU initializes all inputs, outputs, registers, internal peripherals and variables. In task  204  the MCU sets its frequency of operation and timer prescalers. In task  206  the MCU reads any calibration data stored in non-volatile memory and performs a self-calibration. At the end of task  206  the MCU enables interrupts. In task  208  the MCU determines if there is battery on one side only to wake up on that side by initializing the variables accordingly. The MCU then jumps to the main program  210 .  
         [0035]     The main program  210  is similar to a multitasking operating system in which the task priorities and schedules are fixed. It calls the required routines to perform all tasks.  
         [0036]     In task  212  ACQUIRE SIDE A STATUS, the MCU reads the I/O flags, variables, analog to digital conversion registers and counters to determine the status of line A. The status includes but is not limited to on-hook, off-hook, ringing, distinctive ringing, no battery, 60 Hz noise, battery voltage and transition flags from one state to the next for each status variables. The 60 Hz noise detection is used to discriminate between valid signals and 60 Hz noise present on the telephone line. Prior art designs such as Ninh use low impedance ring detectors not susceptible to 60 Hz noise. The ATLS uses a very high impedance line interface and ring detector requiring new and innovative ways to overcome its apparent limitations.  
         [0037]     In task  214  the status of line B is acquired.  
         [0038]     In task  216  the MCU acquires events including but not limited to dialtone detection, stuttering dialtone, hook flash, CallerID messages, DTMF, tones, incoming call detection and outgoing call detection. The CallerID routine reads and decodes the CallerID bits and assembles the messages. These events are time related. For example: the dialtone detection reads the outgoing call flags set by the status task to determine if it is time to look for dialtone. It then detects if dialtone is present for up to four seconds and sets the dialtone-detected flag accordingly.  
         [0039]     The acquire side B events  218  performs the same tasks on the side B.  
         [0040]     An arbitration task  220  performs an analysis of the signals and activity of each side and determines the desired state of the relay, i.e.: on which side the relay should be. This is done by assigning a weight to each side and toggling a SideA/SideB bit according to the highest weight (max=255 min=0). This method is embodied with the following tasks: task  222  takes into account special conditions requiring a suspension of arbitration. The most important of these special conditions is off-hook. To avoid disconnecting a subscriber while he or she is using the telephone, the arbitration tasks must be suspended until the call is terminated. Another special condition suspends the arbitration temporarily for new installations when both local telephone networks may be active. The arbitration task is also suspended when there is battery only on one local telephone network since it is not required. Arbitration may also be suspended as a result of special conditions that may be implemented to force the switch to one side. Task  224  ensures the weights of both sides are never equal to avoid a lock-up situation. Task  226  then proceed to evaluate the conditions to increment the sideA weight. Off-hook followed by dialtone detection, ringing, distinctive ringing, CallerID, Tones, DTMF digits, hook flashes, battery voltage contribute to increase the weight. The task  226  then proceeds to evaluate conditions that decrease the weight of the sideA. Off-Hook without dialtone, no battery, no activity, tones, specific CallerID messages, specific DTMF signals serve to decrease the weight. Task  228  repeats the incremental and decremental functions for the SideB. A no battery condition is detected and taken into account when updating the weights of each line by decrementing the weight at a slower pace than the ATLS hold-up time. Thus if a power failure caused a loss of battery, the ATLS will hold its switch side as long as possible. Task  230  then compares the two weights and when the weight of one side is higher than the other side, the task updates the SideA/SideB bit. Task  232  can be added to perform specialized switching functions. For example it can switch to SideB only when SideA is idle and there is ringing on SideB. It can then return to SideA after the call is terminated.  
         [0041]     The Watchdog task  240  reads the SideA/SideB bit and resets the opposite side watchdog to inhibit it. This ensures the relay is on the correct side. The uninhibited watchdog continuously forces the relay to its side because it is not inhibited. The internal MCU watchdog  167  is periodically reset to ensure proper software execution.  
         [0042]     The Communications task  242  communicates status information by pulsing the LED  163  at varying rates. It is also used to output tones to the telephone line.  
         [0043]     The Power Management task  244  puts the MCU in sleep mode when required. Some power management functions are implemented in other tasks. The dial tone task powers the dial tone detection circuit and comparators only when required. The MCU then cycles back to the start of MAIN.  
         [0044]     The Interrupts task  250  is activated by interrupts. It determines the source of the interrupts and executes the corresponding routines. One routine respond to pulsing of the MCU inputs  170 C,  170 E by updating counters to determine the relative period between pulses. This information is made available to other tasks. The internal timer interrupt routine maintains a time reference used to time functions and events. It also updated several count down timers used by other tasks.  
       OTHER EMBODIMENTS  
       [0045]      FIG. 9  is an alternate embodiment of the telephone line switch. The common circuitry is placed on each side and is called Line Interface and Control  300  and  300 A. Only two isolators  60  and  61 A are required to exchange information between the two MCUs. The communication task is modified in this embodiment to perform an information exchange between the two MCUs. The acquire-status and acquire-event tasks of opposite sides use the communication task instead of the directly connected hardware discussed earlier. The modular design of the software discussed above enables suspension of the arbitration task on the MCU that is not connected to the telephone line based on the SideA/SideB flag. Still another embodiment expands the number of telephone lines.  FIG. 10  shows how this can be accomplished by replacing relay  58  with single pole relays  58 A and  58 B and cascading the circuits enclosed in dotted line  310 . A communication path between all interface and control circuit is required for this embodiment. This can be implemented with opto-isolators  60 ,  60 A,  61  and  61 A between each circuit or by using a bus type communication structure where the isolators are transformers or capacitors. Protection circuit  50 A is added if it is anticipated the additional network connections will have a very long local telephone line. Since the ATLS is capable of many measurements and can communicate through the telephone line, another embodiment adds line testing and reporting functionality. The present embodiment of the ATLS, designed to operate at the customer-premises end of the local telephone network, does not preclude placing it at the originating end of the local telephone network. The MCU internal circuits can be embodied in external components.